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Motor oil, engine oil, or engine lubricant is any one of various substances used for the
lubrication Lubrication is the process or technique of using a lubricant to reduce friction and wear and tear in a contact between two surfaces. The study of lubrication is a discipline in the field of tribology. Lubrication mechanisms such as fluid-lubric ...
of
internal combustion engine An internal combustion engine (ICE or IC engine) is a heat engine in which the combustion of a fuel occurs with an oxidizer (usually air) in a combustion chamber that is an integral part of the working fluid flow circuit. In an internal co ...
s. They typically consist of
base oil Base oils are used to manufacture products including lubricating greases, motor oil and metalworking fluid, metal processing fluids. Different products require different compositions and properties in the oil. One of the most important factors is t ...
s enhanced with various additives, particularly
antiwear additive AW additives, or antiwear additives, are additives for lubricants to prevent metal-to-metal contact between parts of gears. EP additives are used in applications such as gearboxes, while AW additives are used with lighter loads such as bushings. ...
s, detergents,
dispersant A dispersant or a dispersing agent is a substance, typically a surfactant, that is added to a suspension of solid or liquid particles in a liquid (such as a colloid or emulsion) to improve the separation of the particles and to prevent their set ...
s, and, for multi-grade oils, viscosity index improvers. The main function of motor oil is to reduce
friction Friction is the force resisting the relative motion of solid surfaces, fluid layers, and material elements sliding (motion), sliding against each other. There are several types of friction: *Dry friction is a force that opposes the relative la ...
and
wear Wear is the damaging, gradual removal or deformation of material at solid surfaces. Causes of wear can be mechanical (e.g., erosion) or chemical (e.g., corrosion). The study of wear and related processes is referred to as tribology. Wear in ...
on
moving parts Machines include both fixed and moving parts. The moving parts have controlled and constrained motions. Moving parts are machine components excluding any moving fluids, such as fuel, coolant or hydraulic fluid. Moving parts also do not include ...
and to clean the engine from sludge (one of the functions of
dispersant A dispersant or a dispersing agent is a substance, typically a surfactant, that is added to a suspension of solid or liquid particles in a liquid (such as a colloid or emulsion) to improve the separation of the particles and to prevent their set ...
s) and varnish (detergents). It also neutralizes acids that originate from fuel and from oxidation of the
lubricant A lubricant (sometimes shortened to lube) is a substance that helps to reduce friction between surfaces in mutual contact, which ultimately reduces the heat generated when the surfaces move. It may also have the function of transmitting forces, t ...
(detergents), improves sealing of piston rings, and cools the engine by carrying
heat In thermodynamics, heat is defined as the form of energy crossing the boundary of a thermodynamic system by virtue of a temperature difference across the boundary. A thermodynamic system does not ''contain'' heat. Nevertheless, the term is ...
away from moving parts. In addition to the aforementioned basic constituents, almost all lubricating oils contain corrosion and oxidation inhibitors. Motor oil may be composed of only a lubricant base stock in the case of non-
detergent A detergent is a surfactant or a mixture of surfactants with cleansing properties when in dilute solutions. There are a large variety of detergents, a common family being the alkylbenzene sulfonates, which are soap-like compounds that are m ...
oil, or a lubricant base stock plus additives to improve the oil's detergency, extreme pressure performance, and ability to
inhibit Inhibitor or inhibition may refer to: In biology * Enzyme inhibitor, a substance that binds to an enzyme and decreases the enzyme's activity * Reuptake inhibitor, a substance that increases neurotransmission by blocking the reuptake of a neurotr ...
corrosion Corrosion is a natural process that converts a refined metal into a more chemically stable oxide. It is the gradual deterioration of materials (usually a metal) by chemical or electrochemical reaction with their environment. Corrosion engi ...
of engine parts. Motor oils are blended using base oils composed of
petroleum Petroleum, also known as crude oil, or simply oil, is a naturally occurring yellowish-black liquid mixture of mainly hydrocarbons, and is found in geological formations. The name ''petroleum'' covers both naturally occurring unprocessed crude ...
-based
hydrocarbon In organic chemistry, a hydrocarbon is an organic compound consisting entirely of hydrogen and carbon. Hydrocarbons are examples of group 14 hydrides. Hydrocarbons are generally colourless and hydrophobic, and their odors are usually weak or ...
s, polyalphaolefins (PAO), or their mixtures in various proportions, sometimes with up to 20% by weight of
ester In chemistry, an ester is a compound derived from an oxoacid (organic or inorganic) in which at least one hydroxyl group () is replaced by an alkoxy group (), as in the substitution reaction of a carboxylic acid and an alcohol. Glycerides ...
s for better dissolution of additives.


History

On 6 September 1866, American John Ellis founded the Continuous Oil Refining Company. While studying the possible healing powers of crude oil, Dr. Ellis was disappointed to find no real medicinal value, but was intrigued by its potential lubricating properties. He eventually abandoned the medical practice to devote his time to the development of an all-petroleum, high-
viscosity The viscosity of a fluid is a measure of its resistance to deformation at a given rate. For liquids, it corresponds to the informal concept of "thickness": for example, syrup has a higher viscosity than water. Viscosity quantifies the inte ...
lubricant for steam engines – which at the time were using inefficient combinations of petroleum and animal and vegetable fats. He made his breakthrough when he developed an oil that worked effectively at high temperatures. This meant fewer gummed up valves and corroded cylinders.


Use

Motor oil is a
lubricant A lubricant (sometimes shortened to lube) is a substance that helps to reduce friction between surfaces in mutual contact, which ultimately reduces the heat generated when the surfaces move. It may also have the function of transmitting forces, t ...
used in
internal combustion engine An internal combustion engine (ICE or IC engine) is a heat engine in which the combustion of a fuel occurs with an oxidizer (usually air) in a combustion chamber that is an integral part of the working fluid flow circuit. In an internal co ...
s, which power
car A car or automobile is a motor vehicle with wheels. Most definitions of ''cars'' say that they run primarily on roads, seat one to eight people, have four wheels, and mainly transport people instead of goods. The year 1886 is regarded as t ...
s,
motorcycle A motorcycle (motorbike, bike, or trike (if three-wheeled)) is a two or three-wheeled motor vehicle steered by a handlebar. Motorcycle design varies greatly to suit a range of different purposes: long-distance travel, commuting, cruisin ...
s,
lawnmower A lawn mower (also known as a mower, grass cutter or lawnmower) is a device utilizing one or more revolving blades (or a reel) to cut a grass surface to an even height. The height of the cut grass may be fixed by the design of the mower, but g ...
s,
engine-generator An engine–generator is the combination of an electrical generator and an engine ( prime mover) mounted together to form a single piece of equipment. This combination is also called an ''engine–generator set'' or a ''gen-set''. In many context ...
s, and many other machines. In engines, there are parts which move against each other, and the
friction Friction is the force resisting the relative motion of solid surfaces, fluid layers, and material elements sliding (motion), sliding against each other. There are several types of friction: *Dry friction is a force that opposes the relative la ...
between the parts wastes otherwise useful power by converting
kinetic energy In physics, the kinetic energy of an object is the energy that it possesses due to its motion. It is defined as the work needed to accelerate a body of a given mass from rest to its stated velocity. Having gained this energy during its a ...
into
heat In thermodynamics, heat is defined as the form of energy crossing the boundary of a thermodynamic system by virtue of a temperature difference across the boundary. A thermodynamic system does not ''contain'' heat. Nevertheless, the term is ...
. It also
wear Wear is the damaging, gradual removal or deformation of material at solid surfaces. Causes of wear can be mechanical (e.g., erosion) or chemical (e.g., corrosion). The study of wear and related processes is referred to as tribology. Wear in ...
s away those parts, which could lead to lower efficiency and degradation of the engine. Proper
lubrication Lubrication is the process or technique of using a lubricant to reduce friction and wear and tear in a contact between two surfaces. The study of lubrication is a discipline in the field of tribology. Lubrication mechanisms such as fluid-lubric ...
decreases fuel consumption, decreases wasted power, and increases engine longevity. Lubricating oil creates a separating film between surfaces of adjacent moving parts to minimize direct contact between them, decreasing frictional heat and reducing wear, thus protecting the engine. In use, motor oil transfers heat through conduction as it flows through the engine. In an engine with a recirculating oil pump, this heat is transferred by means of airflow over the exterior surface of the oil pan, airflow through an
oil cooler Oil cooling is the use of engine oil as a coolant, typically to remove surplus heat from an internal combustion engine. The hot engine transfers heat to the oil which then usually passes through a heat-exchanger, typically a type of radiator kno ...
, and through oil gases evacuated by the positive crankcase ventilation (PCV) system. While modern recirculating pumps are typically provided in passenger cars and other engines of similar or larger in size, total-loss oiling is a design option that remains popular in small and miniature engines. In petrol (gasoline) engines, the top
piston ring A piston ring is a metallic split ring that is attached to the outer diameter of a piston in an internal combustion engine or steam engine. The main functions of piston rings in engines are: # Sealing the combustion chamber so that there is mini ...
can expose the motor oil to temperatures of . In diesel engines, the top ring can expose the oil to temperatures over . Motor oils with higher viscosity indices thin less at these higher temperatures. Coating metal parts with oil also keeps them from being exposed to
oxygen Oxygen is the chemical element with the symbol O and atomic number 8. It is a member of the chalcogen group in the periodic table, a highly reactive nonmetal, and an oxidizing agent that readily forms oxides with most elements as we ...
, inhibiting
oxidation Redox (reduction–oxidation, , ) is a type of chemical reaction in which the oxidation states of substrate change. Oxidation is the loss of electrons or an increase in the oxidation state, while reduction is the gain of electrons or a ...
at elevated
operating temperature An operating temperature is the allowable temperature range of the local ambient environment at which an electrical or mechanical device operates. The device will operate effectively within a specified temperature range which varies based on the de ...
s preventing
rust Rust is an iron oxide, a usually reddish-brown oxide formed by the reaction of iron and oxygen in the catalytic presence of water or air moisture. Rust consists of hydrous iron(III) oxides (Fe2O3·nH2O) and iron(III) oxide-hydroxide (FeO(OH), ...
or
corrosion Corrosion is a natural process that converts a refined metal into a more chemically stable oxide. It is the gradual deterioration of materials (usually a metal) by chemical or electrochemical reaction with their environment. Corrosion engi ...
.
Corrosion inhibitor In chemistry, a corrosion inhibitor or anti-corrosive is a chemical compound that, when added to a liquid or gas, decreases the corrosion rate of a material, typically a metal or an alloy, that comes into contact with the fluid. The effectiveness ...
s may also be added to the motor oil. Many motor oils also have
detergent A detergent is a surfactant or a mixture of surfactants with cleansing properties when in dilute solutions. There are a large variety of detergents, a common family being the alkylbenzene sulfonates, which are soap-like compounds that are m ...
s and
dispersant A dispersant or a dispersing agent is a substance, typically a surfactant, that is added to a suspension of solid or liquid particles in a liquid (such as a colloid or emulsion) to improve the separation of the particles and to prevent their set ...
s added to help keep the engine clean and minimize oil sludge build-up. The oil is able to trap soot from combustion in itself, rather than leaving it deposited on the internal surfaces. It is a combination of this and some singeing that turns used oil black after some running. Rubbing of metal engine parts inevitably produces some microscopic metallic particles from the
wear Wear is the damaging, gradual removal or deformation of material at solid surfaces. Causes of wear can be mechanical (e.g., erosion) or chemical (e.g., corrosion). The study of wear and related processes is referred to as tribology. Wear in ...
ing of the surfaces. Such particles could circulate in the oil and grind against moving parts, causing wear. Because particles accumulate in the oil, it is typically circulated through an
oil filter An oil filter is a filter designed to remove contaminants from engine oil, transmission oil, lubricating oil, or hydraulic oil. Their chief use is in internal-combustion engines for motor vehicles (both on- and off-road ), powered aircraft, ...
to remove harmful particles. An oil pump, a vane or
gear pump A gear pump uses the meshing of gears to pump fluid by displacement. They are one of the most common types of pumps for hydraulic fluid power applications. The gear pump was invented around 1600 by Johannes Kepler. Gear pumps are also wid ...
powered by the engine, pumps the oil throughout the engine, including the oil filter. Oil filters can be a ''full flow'' or ''bypass'' type. In the
crankcase In a piston engine, the crankcase is the housing that surrounds the crankshaft. In most modern engines, the crankcase is integrated into the engine block. Two-stroke engines typically use a crankcase-compression design, resulting in the fuel/ ...
of a vehicle engine, motor oil lubricates rotating or sliding surfaces between the crankshaft journal bearings (main bearings and big-end bearings) and rods connecting the
piston A piston is a component of reciprocating engines, reciprocating pumps, gas compressors, hydraulic cylinders and pneumatic cylinders, among other similar mechanisms. It is the moving component that is contained by a cylinder and is made gas- ...
s to the crankshaft. The oil collects in an oil pan, or
sump A sump is a low space that collects often undesirable liquids such as water or chemicals. A sump can also be an infiltration basin used to manage surface runoff water and recharge underground aquifers. Sump can also refer to an area in a cav ...
, at the bottom of the crankcase. In some small engines such as lawn mower engines, dippers on the bottoms of connecting rods dip into the oil at the bottom and splash it around the crankcase as needed to lubricate parts inside. In modern vehicle engines, the oil pump takes oil from the oil pan and sends it through the oil filter into oil galleries, from which the oil lubricates the main bearings holding the crankshaft up at the main journals and camshaft bearings operating the valves. In typical modern vehicles, oil pressure-fed from the oil galleries to the main bearings enters holes in the main journals of the crankshaft. From these holes in the main journals, the oil moves through passageways inside the crankshaft to exit holes in the rod journals to lubricate the rod bearings and connecting rods. Some simpler designs relied on these rapidly moving parts to splash and lubricate the contacting surfaces between the piston rings and interior surfaces of the cylinders. However, in modern designs, there are also passageways through the rods which carry oil from the rod bearings to the rod-piston connections and lubricate the contacting surfaces between the piston rings and interior surfaces of the
cylinder A cylinder (from ) has traditionally been a three-dimensional solid, one of the most basic of curvilinear geometric shapes. In elementary geometry, it is considered a prism with a circle as its base. A cylinder may also be defined as an infi ...
s. This oil film also serves as a seal between the piston rings and cylinder walls to separate the
combustion chamber A combustion chamber is part of an internal combustion engine in which the fuel/air mix is burned. For steam engines, the term has also been used for an extension of the firebox which is used to allow a more complete combustion process. Intern ...
in the
cylinder head In an internal combustion engine, the cylinder head (often abbreviated to simply "head") sits above the cylinder (engine), cylinders and forms the roof of the combustion chamber. In sidevalve engines, the head is a simple sheet of metal; whereas ...
from the crankcase. The oil then drips back down into the oil pan. Motor oil may also serve as a cooling agent. In some engines oil is sprayed through a nozzle inside the crankcase onto the piston to provide cooling of specific parts that undergo high-temperature strain. On the other hand, the
thermal capacity Heat capacity or thermal capacity is a physical property of matter, defined as the amount of heat to be supplied to an object to produce a unit change in its temperature. The SI unit of heat capacity is joule per kelvin (J/K). Heat capacity i ...
of the oil pool has to be filled, i.e. the oil has to reach its designed temperature range before it can protect the engine under high load. This typically takes longer than heating the main
cooling agent A coolant is a substance, typically liquid, that is used to reduce or regulate the temperature of a system. An ideal coolant has high thermal capacity, low viscosity, is low-cost, non-toxic, chemically inert and neither causes nor promotes corrosio ...
water or mixtures thereofup to its operating temperature. In order to inform the driver about the oil temperature, some older and most high-performance or racing engines feature an oil
thermometer A thermometer is a device that measures temperature or a temperature gradient (the degree of hotness or coldness of an object). A thermometer has two important elements: (1) a temperature sensor (e.g. the bulb of a mercury-in-glass thermomete ...
. Continued operation of an internal combustion engine without adequate engine oil can cause damage to the engine, first by wear and tear, and in extreme cases by "engine seizure" where the lack of lubrication and cooling causes the engine to cease operation suddenly. Engine seizure can cause extensive damage to the engine mechanisms.


Non-vehicle motor oils

An example is lubricating oil for
four-stroke A four-stroke (also four-cycle) engine is an internal combustion (IC) engine in which the piston completes four separate strokes while turning the crankshaft. A stroke refers to the full travel of the piston along the cylinder, in either direct ...
or four-cycle internal combustion engines such as those used in portable electricity generators and "walk behind" lawn mowers. Another example is
two-stroke oil Two-stroke oil (also referred to as two-cycle oil, 2-cycle oil, 2T oil, or 2-stroke oil) is a special type of motor oil intended for use in crankcase compression two-stroke engines, typical of small gasoline-powered engines. Use Unlike a four- ...
for lubrication of
two-stroke A two-stroke (or two-stroke cycle) engine is a type of internal combustion engine that completes a power cycle with two strokes (up and down movements) of the piston during one power cycle, this power cycle being completed in one revolution of t ...
or two-cycle internal combustion engines found in
snow blower A snow blower or snow thrower is a machine for removing snow from an area where it is problematic, such as a driveway, sidewalk, roadway, railroad track, ice rink, or runway. The commonly used term "snow blower" is a misnomer, as the snow ...
s, chain saws, model airplanes, gasoline-powered gardening equipment like hedge trimmers,
leaf blower A leaf blower, commonly known as a blower, is a device that propels air out of a nozzle to move debris such as leaves and grass cuttings. Leaf blowers are powered by electric or gasoline motors. Gasoline models have traditionally been two-str ...
s and soil cultivators. Often, these motors are not exposed to as wide of service temperature ranges as in vehicles, so these oils may be single viscosity oils. In small two-stroke engines, the oil may be pre-mixed with the gasoline or fuel, often in a rich gasoline:oil ratio of 25:1, 40:1 or 50:1, and burned in use along with the gasoline. Larger two-stroke engines used in boats and motorcycles may have a more economical oil injection system rather than oil pre-mixed into the gasoline. The oil injection system is not used on small engines used in applications like snowblowers and trolling motors as the oil injection system is too expensive for small engines and would take up too much room on the equipment. The oil properties will vary according to the individual needs of these devices. Non-smoking two-stroke oils are composed of esters or polyglycols. Environmental legislation for leisure marine applications, especially in Europe, encouraged the use of ester-based two cycle oil.


Properties

Most motor oils are made from a heavier, thicker
petroleum Petroleum, also known as crude oil, or simply oil, is a naturally occurring yellowish-black liquid mixture of mainly hydrocarbons, and is found in geological formations. The name ''petroleum'' covers both naturally occurring unprocessed crude ...
hydrocarbon In organic chemistry, a hydrocarbon is an organic compound consisting entirely of hydrogen and carbon. Hydrocarbons are examples of group 14 hydrides. Hydrocarbons are generally colourless and hydrophobic, and their odors are usually weak or ...
base stock derived from crude oil, with additives to improve certain properties. The bulk of a typical motor oil consists of
hydrocarbon In organic chemistry, a hydrocarbon is an organic compound consisting entirely of hydrogen and carbon. Hydrocarbons are examples of group 14 hydrides. Hydrocarbons are generally colourless and hydrophobic, and their odors are usually weak or ...
s with between 18 and 34
carbon Carbon () is a chemical element with the symbol C and atomic number 6. It is nonmetallic and tetravalent—its atom making four electrons available to form covalent chemical bonds. It belongs to group 14 of the periodic table. Carbon makes ...
atom Every atom is composed of a nucleus and one or more electrons bound to the nucleus. The nucleus is made of one or more protons and a number of neutrons. Only the most common variety of hydrogen has no neutrons. Every solid, liquid, gas ...
s per
molecule A molecule is a group of two or more atoms held together by attractive forces known as chemical bonds; depending on context, the term may or may not include ions which satisfy this criterion. In quantum physics, organic chemistry, and bio ...
. One of the most important properties of motor oil in maintaining a lubricating film between moving parts is its
viscosity The viscosity of a fluid is a measure of its resistance to deformation at a given rate. For liquids, it corresponds to the informal concept of "thickness": for example, syrup has a higher viscosity than water. Viscosity quantifies the inte ...
. The viscosity of a liquid can be thought of as its "thickness" or a measure of its resistance to flow. The viscosity must be high enough to maintain a lubricating film, but low enough that the oil can flow around the engine parts under all conditions. The
viscosity index The viscosity index (VI) is an arbitrary, unit-less measure of a fluid's change in viscosity relative to temperature change. It is mostly used to characterize the viscosity-temperature behavior of lubricating oils. The lower the VI, the more the v ...
is a measure of how much the oil's viscosity changes as temperature changes. A higher viscosity index indicates the viscosity changes less with temperature than a lower viscosity index. Motor oil must be able to flow adequately at the lowest temperature it is expected to experience in order to minimize metal to metal contact between moving parts upon starting up the engine. The ''pour point'' defined first this property of motor oil, as defined by ASTM D97 as "...an index of the lowest temperature of its utility..." for a given application, but the
cold-cranking simulator The cold-cranking simulator (CCS) is a device used to determine the low temperature performance of lubricants, when starting a cold engine (i.e. cold-cranking). In this condition, the only energy available to turn the engine comes from the starter ...
(CCS, see ASTM D5293-08) and mini-rotary viscometer (MRV, see ASTM D3829-02(2007), ASTM D4684-08) are today the properties required in motor oil specs and define the
Society of Automotive Engineers SAE International, formerly named the Society of Automotive Engineers, is a United States-based, globally active professional association and standards developing organization for engineering professionals in various industries. SAE Internatio ...
(SAE) classifications. Oil is largely composed of hydrocarbons which can burn if ignited. Still another important property of motor oil is its
flash point The flash point of a material is the "lowest liquid temperature at which, under certain standardized conditions, a liquid gives off vapours in a quantity such as to be capable of forming an ignitable vapour/air mixture". (EN 60079-10-1) The fl ...
, the lowest temperature at which the oil gives off vapors which can ignite. It is dangerous for the oil in a motor to ignite and burn, so a high flash point is desirable. At a
petroleum refinery An oil refinery or petroleum refinery is an industrial process plant where petroleum (crude oil) is transformed and refined into useful products such as gasoline (petrol), diesel fuel, asphalt base, fuel oils, heating oil, kerosene, liquefi ...
,
fractional distillation Fractional distillation is the separation of a mixture into its component parts, or fractions. Chemical compounds are separated by heating them to a temperature at which one or more fractions of the mixture will vaporize. It uses distillation to ...
separates a motor oil fraction from other crude oil fractions, removing the more volatile components, and therefore increasing the oil's flash point (reducing its tendency to burn). Another manipulated property of motor oil is its
total base number Total Base Number (TBN) is a measurement of basicity that is expressed in terms of the number of milligrams of potassium hydroxide per gram of oil sample (mg KOH/g). TBN is an important measurement in petroleum products, and the value varies depend ...
(TBN), which is a measurement of the reserve
alkalinity Alkalinity (from ar, القلوي, al-qaly, lit=ashes of the saltwort) is the capacity of water to resist acidification. It should not be confused with basicity, which is an absolute measurement on the pH scale. Alkalinity is the strengt ...
of an oil, meaning its ability to neutralize acids. The resulting quantity is determined as mg KOH/ (gram of lubricant). Analogously,
total acid number The total acid number (TAN) is a measurement of acidity that is determined by the amount of potassium hydroxide in milligrams that is needed to neutralize the acids in one gram of oil. It is an important quality measurement of crude oil. The TAN ...
(TAN) is the measure of a lubricant's
acidity In computer science, ACID ( atomicity, consistency, isolation, durability) is a set of properties of database transactions intended to guarantee data validity despite errors, power failures, and other mishaps. In the context of databases, a sequ ...
. Other tests include
zinc Zinc is a chemical element with the symbol Zn and atomic number 30. Zinc is a slightly brittle metal at room temperature and has a shiny-greyish appearance when oxidation is removed. It is the first element in group 12 (IIB) of the periodic t ...
,
phosphorus Phosphorus is a chemical element with the symbol P and atomic number 15. Elemental phosphorus exists in two major forms, white phosphorus and red phosphorus, but because it is highly reactive, phosphorus is never found as a free element on Ea ...
, or
sulfur Sulfur (or sulphur in British English) is a chemical element with the symbol S and atomic number 16. It is abundant, multivalent and nonmetallic. Under normal conditions, sulfur atoms form cyclic octatomic molecules with a chemical formul ...
content, and testing for excessive
foam Foams are materials formed by trapping pockets of gas in a liquid or solid. A bath sponge and the head on a glass of beer are examples of foams. In most foams, the volume of gas is large, with thin films of liquid or solid separating the ...
ing. The
Noack volatility test The Noack volatility test, named after Kurt Noack, determines the evaporation loss of lubricants A lubricant (sometimes shortened to lube) is a substance that helps to reduce friction between surfaces in mutual contact, which ultimately reduces ...
(ASTM D-5800) determines the physical evaporation loss of lubricants in high temperature service. A maximum of 14% evaporation loss is allowable to meet API SL and ILSAC GF-3 specifications. Some automotive OEM oil specifications require lower than 10%. Table of thermal and physical properties of typical unused engine oil:


Viscosity grades

The
Society of Automotive Engineers SAE International, formerly named the Society of Automotive Engineers, is a United States-based, globally active professional association and standards developing organization for engineering professionals in various industries. SAE Internatio ...
(SAE) has established a numerical code system for grading motor oils according to their
viscosity The viscosity of a fluid is a measure of its resistance to deformation at a given rate. For liquids, it corresponds to the informal concept of "thickness": for example, syrup has a higher viscosity than water. Viscosity quantifies the inte ...
characteristics known as
SAE SAE or Sae may refer to: Science and technology : * Selective area epitaxy, local growth of epitaxial layer through a patterned dielectric mask deposited on a semiconductor substrate * Serious adverse event, in a clinical trial * Simultaneous Auth ...
J300. This standard is commonly used throughout the world, and standards organizations that do so include API and
ACEA Acea is a surname. Notable people with the surname include: * Eusebio Acea (born 1969), Cuban rower * Francis Acea (born 1967), Cuban artist *John Adriano Acea (1917–1963), American jazz pianist *Raidel Acea Raidel Acea Morales (born 21 Octo ...
. The grades include single grades, such as SAE 30, and also multi-grades such as SAE 15W-30. A multi-grade consists of a winter grade specifying the viscosity at cold temperatures and a non-winter grade specifying the viscosity at operating temperatures. An engine oil using a polymeric viscosity index improver (VII) must be classified as multi-grade. Breakdown of VIIs under shear is a concern in motorcycle applications, where the
transmission Transmission may refer to: Medicine, science and technology * Power transmission ** Electric power transmission ** Propulsion transmission, technology allowing controlled application of power *** Automatic transmission *** Manual transmission ** ...
may share lubricating oil with the motor. For this reason, motorcycle-specific oil is sometimes recommended. The necessity of higher-priced motorcycle-specific oil has also been challenged by at least one consumer organization.


Maintenance

The oil and the
oil filter An oil filter is a filter designed to remove contaminants from engine oil, transmission oil, lubricating oil, or hydraulic oil. Their chief use is in internal-combustion engines for motor vehicles (both on- and off-road ), powered aircraft, ...
need to be periodically replaced; the process is called an oil change. While there is an entire industry surrounding regular oil changes and maintenance, an oil change is a relatively simple car maintenance operation that many car owners can do themselves. It involves draining the oil from the engine into a drip pan, replacing the filter, and adding fresh oil. In engines, there is some exposure of the oil to products of internal combustion, and microscopic coke particles from black
soot Soot ( ) is a mass of impure carbon particles resulting from the incomplete combustion of hydrocarbons. It is more properly restricted to the product of the gas-phase combustion process but is commonly extended to include the residual pyrolyse ...
accumulate in the oil during operation. Also, the rubbing of metal engine parts produces some microscopic metallic particles from the wearing of the surfaces. Such particles could circulate in the oil and grind against the part surfaces causing
wear Wear is the damaging, gradual removal or deformation of material at solid surfaces. Causes of wear can be mechanical (e.g., erosion) or chemical (e.g., corrosion). The study of wear and related processes is referred to as tribology. Wear in ...
. The
oil filter An oil filter is a filter designed to remove contaminants from engine oil, transmission oil, lubricating oil, or hydraulic oil. Their chief use is in internal-combustion engines for motor vehicles (both on- and off-road ), powered aircraft, ...
removes many of the particles and sludge, but eventually, the oil filter can become clogged, if used for extremely long periods. The motor oil and especially the additives also undergo thermal and mechanical degradation, which reduces the viscosity and reserve alkalinity of the oil. At reduced viscosity, the oil is not as capable of lubricating the engine, thus increasing wear and the chance of overheating. Reserve alkalinity is the ability of the oil to resist the formation of acids. Should the reserve alkalinity decline to zero, those acids form and corrode the engine. Some engine manufacturers specify which
Society of Automotive Engineers SAE International, formerly named the Society of Automotive Engineers, is a United States-based, globally active professional association and standards developing organization for engineering professionals in various industries. SAE Internatio ...
(SAE)
viscosity The viscosity of a fluid is a measure of its resistance to deformation at a given rate. For liquids, it corresponds to the informal concept of "thickness": for example, syrup has a higher viscosity than water. Viscosity quantifies the inte ...
grade of oil should be used, but different viscosity motor oil may perform better based on the operating environment. Many manufacturers have varying requirements and have designations for motor oil they require to be used. This is driven by the EPA requirement that the same viscosity grade of oil used in the MPG test must be recommended to the customer. This exclusive recommendation led to the elimination of informative charts depicting climate temperature range along with several corresponding oil viscosity grades being suggested. In general, unless specified by the manufacturer, thicker oils are not necessarily better than thinner oils; heavy oils tend to stick longer to parts between two moving surfaces, and this degrades the oil faster than a lighter oil that flows better, allowing fresh oil in its place sooner. Cold weather has a thickening effect on conventional oil, and this is one reason thinner oils are manufacturer recommended in places with cold winters. Motor oil changes are usually scheduled based on the time in service or the distance that the vehicle has traveled. These are rough indications of the real factors that control when an oil change is appropriate, which include how long the oil has been run at elevated temperatures, how many heating cycles the engine has been through, and how hard the engine has worked. The vehicle distance is intended to estimate the time at high temperature, while the time in service is supposed to correlate with the number of vehicle trips and capture the number of heating cycles. Oil does not degrade significantly just sitting in a cold engine. On the other hand, if a car is driven just for very short distances, the oil will not fully heat up, and it will accumulate contaminants such as water, due to lack of sufficient heat to boil off the water. Oil in this condition, just sitting in an engine, can cause problems. Also important is the quality of the oil used, especially with synthetics (synthetics are more stable than conventional oils). Some manufacturers address this (for example, BMW and VW with their respective long-life standards), while others do not. Time-based intervals account for the short-trip drivers who drive short distances, which build up more contaminants. Manufacturers advise to not exceed their time or distance-driven interval for a motor oil change. Many modern cars now list somewhat higher intervals for changing oil and filter, with the constraint of "severe" service requiring more frequent changes with less-than-ideal driving. This applies to short trips of under , where the oil does not get to full operating temperature long enough to boil off condensation, excess fuel, and other contamination that leads to "sludge", "varnish", "acids", or other deposits. Many manufacturers have engine computer calculations to estimate the oil's condition based on the factors which degrade it, such as RPM, temperature, and trip length; one system adds an optical sensor for determining the clarity of the oil in the engine. These systems are commonly known as Oil Life Monitors or OLMs. Some quick oil change shops recommend intervals of , or every three months; this is not necessary, according to many automobile manufacturers. This has led to a campaign by the California EPA against the "
3,000-mile myth The 3,000 mile myth refers to a common belief, particularly in the United States, that all motor vehicles should have their motor oil changed at least every to maintain their car engine. Efforts are under way to convince the public that this is n ...
", promoting vehicle manufacturer's recommendations for oil change intervals over those of the oil change industry. The engine user can, in replacing the oil, adjust the viscosity for the ambient temperature change, thicker for summer heat and thinner for the winter cold. Lower-viscosity oils are common in newer vehicles. By the mid-1980s, recommended viscosities had moved down to
5W-30 Motor oil, engine oil, or engine lubricant is any one of various substances used for the lubrication of internal combustion engines. They typically consist of base oils enhanced with various additives, particularly antiwear additives, detergen ...
, primarily to improve fuel efficiency. A typical modern application would be Honda motor's use of 5W-20 (and in their newest vehicles, 0W-20) viscosity oil for . Engine designs are evolving to allow the use of even lower-viscosity oils without the risk of excessive metal-to-metal abrasion, principally in the cam and valve mechanism areas. In line with car manufacturers push towards these lower viscosities in search of better fuel economy, on 2 April 2013 the Society of Automotive Engineers (SAE) introduced an SAE 16 viscosity rating, a break from its traditional "divisible by 10" numbering system for its high-temperature viscosity ratings that spanned from low-viscosity SAE 20 to high-viscosity SAE 60.


Standards


American Petroleum Institute (API)

Engine lubricants are evaluated against the
American Petroleum Institute The American Petroleum Institute (API) is the largest U.S. trade association for the oil and natural gas industry. It claims to represent nearly 600 corporations involved in production, refinement, distribution, and many other aspects of the ...
(API), SJ, SL, SM, SN, SP, CH-4, CI-4, CI-4 PLUS, CJ-4, CK, and FA, as well as International Lubricant Standardization and Approval Committee (ILSAC) GF-3, GF-4, and GF-5, and Cummins, Mack and John Deere (and other Original Equipment Manufacturers (OEM)) requirements. These evaluations include chemical and physical properties using bench test methods as well as actual running engine tests to quantify engine sludge, oxidation, component wear, oil consumption, piston deposits and fuel economy. Originally S for spark ignition and C for compression, as used with diesel engines. Many oil producers still refer these categories in their marketing.Oil Categories
API
The API sets minimum performance standards for lubricants. Motor oil is used for the
lubrication Lubrication is the process or technique of using a lubricant to reduce friction and wear and tear in a contact between two surfaces. The study of lubrication is a discipline in the field of tribology. Lubrication mechanisms such as fluid-lubric ...
, cooling, and cleaning of
internal combustion engine An internal combustion engine (ICE or IC engine) is a heat engine in which the combustion of a fuel occurs with an oxidizer (usually air) in a combustion chamber that is an integral part of the working fluid flow circuit. In an internal co ...
s. Motor oil may be composed of only a lubricant base stock in the case of mostly obsolete non-
detergent A detergent is a surfactant or a mixture of surfactants with cleansing properties when in dilute solutions. There are a large variety of detergents, a common family being the alkylbenzene sulfonates, which are soap-like compounds that are m ...
oil, or a lubricant base stock plus additives to improve the oil's detergency, extreme pressure performance, and ability to
inhibit Inhibitor or inhibition may refer to: In biology * Enzyme inhibitor, a substance that binds to an enzyme and decreases the enzyme's activity * Reuptake inhibitor, a substance that increases neurotransmission by blocking the reuptake of a neurotr ...
corrosion Corrosion is a natural process that converts a refined metal into a more chemically stable oxide. It is the gradual deterioration of materials (usually a metal) by chemical or electrochemical reaction with their environment. Corrosion engi ...
of engine parts. Groups: Lubricant base stocks are categorized into five groups by the API. Group I base stocks are composed of fractionally distilled
petroleum Petroleum, also known as crude oil, or simply oil, is a naturally occurring yellowish-black liquid mixture of mainly hydrocarbons, and is found in geological formations. The name ''petroleum'' covers both naturally occurring unprocessed crude ...
which is further refined with solvent extraction processes to improve certain properties such as oxidation resistance and to remove wax. Poorly refined mineral oils that fail to meet the minimum VI of 80 required in group I fit into Group V. Group II base stocks are composed of fractionally distilled
petroleum Petroleum, also known as crude oil, or simply oil, is a naturally occurring yellowish-black liquid mixture of mainly hydrocarbons, and is found in geological formations. The name ''petroleum'' covers both naturally occurring unprocessed crude ...
that has been hydrocracked to further refine and purify it. Group III base stocks have similar characteristics to Group II base stocks, except that Group III base stocks have higher viscosity indexes. Group III base stocks are produced by further hydrocracking of either Group II base stocks or hydroisomerized slack wax (a Group I and II dewaxing process by-product). Group IV base stock are
polyalphaolefin A polyolefin is a type of polymer with the general formula (CH2CHR)n where R is an alkyl group. They are usually derived from a small set of simple olefins (alkenes). Dominant in a commercial sense are polyethylene and polypropylene. More speciali ...
s (PAOs). Group V is a catch-all group for any base stock not described by Groups I to IV. Examples of group V base stocks include polyolesters (POE), polyalkylene glycols (PAG), and perfluoropolyalkylethers (PFPAEs) and poorly refined mineral oil. Groups I and II are commonly referred to as
mineral oil Mineral oil is any of various colorless, odorless, light mixtures of higher alkanes from a mineral source, particularly a distillate of petroleum, as distinct from usually edible vegetable oils. The name 'mineral oil' by itself is imprecise, ...
s, group III is typically referred to as synthetic (except in Germany and Japan, where they must not be called synthetic) and group IV is a synthetic oil. Group V base oils are so diverse that there is no catch-all description. The API service classes have two general classifications: ''S'' for "service/spark ignition" (typical passenger cars and light trucks using
gasoline engine A petrol engine (gasoline engine in American English) is an internal combustion engine designed to run on petrol (gasoline). Petrol engines can often be adapted to also run on fuels such as liquefied petroleum gas and ethanol blends (such as '' ...
s), and ''C'' for "commercial/compression ignition" (typical diesel equipment). Engine oil which has been tested and meets the API standards may display the API Service Symbol (also known as the "Donut") with the service categories on containers sold to oil users. The latest API service category is API SP for gasoline automobile and light-truck engines. The SP standard refers to a group of laboratory and engine tests, including the latest series for control of high-temperature deposits. Current API service categories include SP, SN, SM, SL and SJ for gasoline engines. All earlier service categories are obsolete. Motorcycle oils commonly still use the SF/SG standard though. All the current gasoline categories (including the obsolete SH) have placed limitations on the phosphorus content for certain SAE viscosity grades (the xW-20, xW-30) due to the chemical poisoning that phosphorus has on catalytic converters. Phosphorus is a key anti-wear component in motor oil and is usually found in motor oil in the form of
zinc dithiophosphate Zinc dialkyldithiophosphates (often referred to as ZDDP) are a family of coordination compounds developed in the 1940s that feature zinc bound to the anion of a dialkyldithiophosphoric salt (e.g., ammonium diethyl dithiophosphate). These unchar ...
(ZDDP). Each new API category has placed successively lower phosphorus and zinc limits, and thus has created a controversial issue of obsolescent oils needed for older engines, especially engines with sliding (flat/cleave) tappets. API and ILSAC, which represents most of the world's major automobile/engine manufacturers, state API SM/ILSAC GF-4 is fully backwards compatible, and it is noted that one of the engine tests required for API SM, the Sequence IVA, is a sliding tappet design to test specifically for cam wear protection. Not everyone is in agreement with backwards compatibility, and in addition, there are special situations, such as "performance" engines or fully race built engines, where the engine protection requirements are above and beyond API/ILSAC requirements. Because of this, there are specialty oils out in the market place with higher than API allowed phosphorus levels. Most engines built before 1985 have the flat/cleave bearing style systems of construction, which is sensitive to reducing zinc and phosphorus. For example, in API SG rated oils, this was at the 1200–1300 ppm level for zinc and phosphorus, where the current SM is under 600 ppm. This reduction in anti-wear chemicals in oil has caused premature failures of camshafts and other high pressure bearings in many older automobiles and has been blamed for premature failure of the oil pump drive/cam position sensor gear that is meshed with camshaft gear in some modern engines. The current
diesel engine The diesel engine, named after Rudolf Diesel, is an internal combustion engine in which ignition of the fuel is caused by the elevated temperature of the air in the cylinder due to mechanical compression; thus, the diesel engine is a so-ca ...
service categories are API CK-4, CJ-4, CI-4 PLUS, CI-4, CH-4, and FA-4. The previous service categories such as API CC or CD are obsolete. API solved problems with API CI-4 by creating a separate API CI-4 PLUS category that contains some additional requirements – this marking is located in the lower portion of the API Service Symbol "Donut". API CK-4 and FA-4 have been introduced for 2017 model American engines. API CK-4 is backward compatible that means API CK-4 oils are assumed to provide superior performance to oils made to previous categories and could be used without problems in all previous model engines (but see Ford below). API FA-4 oils are different (that is why API decided to start a new group in addition to API Sx and API Cx). API FA-4 oils are formulated for enhanced fuel economy (presented as reduced greenhouse gas emission). To achieve that, they are SAE xW-30 oils blended to a high temperature high shear viscosity from 2.9 cP to 3.2 cP. They are not suitable for all engines thus their use depends on the decision of each engine manufacturer. They cannot be used with diesel fuel containing more than 15 ppm sulfur. Cummins reacted to the introduction of API CK-4 and API FA-4 by issuing its CES 20086 list of API CK-4 registered oils and CES 20087 list of API FA-4 registered oils. Valvoline oils are preferred. Ford does not recommend API CK-4 or FA-4 oils in its diesel engines. While engine oils are formulated to meet a specific API service category, they in fact conform closely enough to both the gasoline and diesel categories. Thus diesel rated engine oils usually carry the relevant gasoline categories, e.g. an API CJ-4 oil could show either API SL or API SM on the container. The rule is that the first mentioned category is fully met and the second one is fully met except where its requirements clash with the requirements of the first one.


Motorcycle oil

The API oil classification structure has eliminated specific support for wet-clutch motorcycle applications in their descriptors, and API SJ and newer oils are referred to be specific to automobile and light truck use. Accordingly, motorcycle oils are subject to their own unique standards. See JASO below. As discussed above, motorcycle oils commonly still use the obsolescent SF/SG standard.


ILSAC

The International Lubricant Standardization and Approval Committee (ILSAC) also has standards for motor oil. Introduced in 2004, GF-4ILSAC GF-4 STANDARD FOR PASSENGER CAR ENGINE OILS
January 14, 2004
applies to SAE 0W-20, 5W-20, 0W-30, 5W-30, and 10W-30 viscosity grade oils. In general, ILSAC works with API in creating the newest gasoline oil specification, with ILSAC adding an extra requirement of fuel economy testing to their specification. For GF-4, a Sequence VIB Fuel Economy Test (ASTM D6837) is required that is not required in API service category SM. A key new test for GF-4, which is also required for API SM, is the Sequence IIIG, which involves running a , GM 3.8 L V-6 at , 3,600 rpm, and oil temperature for 100 hours. These are much more severe conditions than any API-specified oil was designed for: cars which typically push their oil temperature consistently above are most
turbocharged In an internal combustion engine, a turbocharger (often called a turbo) is a forced induction device that is powered by the flow of exhaust gases. It uses this energy to compress the intake gas, forcing more air into the engine in order to pro ...
engines, along with most engines of European or Japanese origin, particularly small capacity, high power output. The IIIG test is about 50% more difficult than the previous IIIF test, used in GF-3 and API SL oils. Engine oils bearing the API starburst symbol since 2005 are ILSAC GF-4 compliant. To help consumers recognize that an oil meets the ILSAC requirements, API developed a "starburst" certification mark. A new set of specifications, GF-5, took effect in October 2010. The industry had one year to convert their oils to GF-5 and in September 2011, ILSAC no longer offered licensing for GF-4. After nearly a decade of GF-5, ILSAC released final GF-6 specifications in 2019, with licensed sales to oil manufacturers and re-branders to begin 1 May 2020. There are two GF6 standards; GF-6A being a progression and fully backwards compatible with GF-5, and GF-6B specifically for SAE 0W-16 viscosity oil.


ACEA

The ACEA ('' Association des Constructeurs Européens d'Automobiles'') performance/quality classifications A3/A5 tests used in
Europe Europe is a large peninsula conventionally considered a continent in its own right because of its great physical size and the weight of its history and traditions. Europe is also considered a subcontinent of Eurasia and it is located enti ...
are arguably more stringent than the API and ILSAC standards. CEC (The Co-ordinating European Council) is the development body for fuel and lubricant testing in Europe and beyond, setting the standards via their European Industry groups; ACEA, ATIEL, ATC and CONCAWE. ACEA does not certify oils, nor license, nor register, compliance certificates. Oil manufacturers are themselves responsible for carrying out all oil testing and evaluation according to recognised engine lubricant industry standards and practices. Popular categories include A3/B3 and A3/B4 which are defined as "Stable, stay-in-grade Engine Oil intended for use in Passenger Car & Light Duty Van Gasoline& Diesel Engines with extended drain intervals" A3/B5 is suitable only for engines designed to use low viscosities. Category C oils are designated for use with catalysts and particulate filters while Category E is for heavy duty diesel.


JASO

The Japanese Automotive Standards Organization (JASO) has created their own set of performance and quality standards for petrol engines of Japanese origin. For four-stroke gasoline engines, the JASO T904 standard is used, and is particularly relevant to motorcycle engines. The JASO T904-MA and MA2 standards are designed to distinguish oils that are approved for wet clutch use, with MA2 lubricants delivering higher friction performance. The JASO T904-MB standard denotes oils not suitable for wet clutch use, and are therefore used in scooters equipped with continuously variable transmissions. The addition of friction modifiers to JASO MB oils can contribute to greater fuel economy in these applications. For two-stroke gasoline engines, the JASO M345 (FA, FB, FC, FD) standard is used, and this refers particularly to low ash, lubricity, detergency, low smoke and exhaust blocking. These standards, especially JASO-MA (for motorcycles) and JASO-FC, are designed to address oil-requirement issues not addressed by the API service categories. One element of the JASO-MA standard is a friction test designed to determine suitability for wet clutch usage.Motorcycle Four Cycle Gasoline Engine Oil (JASO T 903:2011) Application Manual. JASO Engine Oil Standards Implementation Panel. May 2011. An oil that meets JASO-MA is considered appropriate for wet clutch operations. Oils marketed as motorcycle-specific will carry the JASO-MA label.


ASTM

A 1989 American Society for Testing and Materials (ASTM) report stated that its 12-year effort to come up with a new high-temperature, high-shear (HTHS) standard was not successful. Referring to SAE J300, the basis for current grading standards, the report stated:
The rapid growth of non-Newtonian multigraded oils has rendered kinematic viscosity as a nearly useless parameter for characterising "real" viscosity in critical zones of an engine... There are those who are disappointed that the twelve-year effort has not resulted in a redefinition of the SAE J300 Engine Oil Viscosity Classification document so as to express high-temperature viscosity of the various grades ... In the view of this writer, this redefinition did not occur because the automotive lubricant market knows of no field failures unambiguously attributable to insufficient HTHS oil viscosity.


Other additives

In addition to the viscosity index improvers, motor oil manufacturers often include other additives such as
detergent A detergent is a surfactant or a mixture of surfactants with cleansing properties when in dilute solutions. There are a large variety of detergents, a common family being the alkylbenzene sulfonates, which are soap-like compounds that are m ...
s and dispersants to help keep the engine clean by minimizing sludge buildup,
corrosion inhibitor In chemistry, a corrosion inhibitor or anti-corrosive is a chemical compound that, when added to a liquid or gas, decreases the corrosion rate of a material, typically a metal or an alloy, that comes into contact with the fluid. The effectiveness ...
s, and alkaline additives to neutralize acidic oxidation products of the oil. Most commercial oils have a minimal amount of
zinc dialkyldithiophosphate Zinc dialkyldithiophosphates (often referred to as ZDDP) are a family of coordination compounds developed in the 1940s that feature zinc bound to the anion of a dialkyldithiophosphoric salt (e.g., ammonium diethyl dithiophosphate). These uncharge ...
as an anti-wear additive to protect contacting metal surfaces with
zinc Zinc is a chemical element with the symbol Zn and atomic number 30. Zinc is a slightly brittle metal at room temperature and has a shiny-greyish appearance when oxidation is removed. It is the first element in group 12 (IIB) of the periodic t ...
and other compounds in case of metal to metal contact. The quantity of zinc dialkyldithiophosphate is limited to minimize adverse effect on
catalytic converter A catalytic converter is an exhaust emission control device that converts toxic gases and pollutants in exhaust gas from an internal combustion engine into less-toxic pollutants by catalyzing a redox reaction. Catalytic converters are usuall ...
s. Another aspect for after-treatment devices is the deposition of oil ash, which increases the exhaust back pressure and reduces fuel economy over time. The so-called "chemical box" limits today the concentrations of sulfur, ash and phosphorus (SAP). There are other additives available commercially which can be added to the oil by the user for purported additional benefit. Some of these additives include: *
Antiwear additive AW additives, or antiwear additives, are additives for lubricants to prevent metal-to-metal contact between parts of gears. EP additives are used in applications such as gearboxes, while AW additives are used with lighter loads such as bushings. ...
s, like
zinc dialkyldithiophosphate Zinc dialkyldithiophosphates (often referred to as ZDDP) are a family of coordination compounds developed in the 1940s that feature zinc bound to the anion of a dialkyldithiophosphoric salt (e.g., ammonium diethyl dithiophosphate). These uncharge ...
(ZDDP) and its alternatives due to phosphorus limits in some specifications. Calcium sulfonates additives are also added to protect motor oil from oxidative breakdown and to prevent the formation of sludge and varnish deposits. Both were the main basis of additive packages used by lubricant manufacturers up until the 1990s when the need for ashless additives arose. Main advantage was very low price and wide availability (sulfonates were originally waste byproducts). Currently there are ashless oil lubricants without these additives, which can only fulfill the qualities of the previous generation with more expensive basestock and more expensive organic or organometallic additive compounds. Some new oils are not formulated to provide the level of protection of previous generations to save manufacturing costs. * Some
molybdenum disulfide Molybdenum disulfide (or moly) is an inorganic compound composed of molybdenum and sulfur. Its chemical formula is . The compound is classified as a transition metal dichalcogenide. It is a silvery black solid that occurs as the mineral molybdeni ...
containing additives to lubricating oils are claimed to reduce friction, bond to metal, or have anti-wear properties. MoS2 particles can be shear-welded on steel surface and some engine components were even treated with MoS2 layer during manufacture, namely liners in engines. (
Trabant Trabant () is a series of small cars produced from 1957 until 1991 by former East German car manufacturer VEB Sachsenring Automobilwerke Zwickau. In total, four different models were made, the Trabant 500, Trabant 600, Trabant 601, and the T ...
for example). They were used in World War II in flight engines and became commercial after World War II until the 1990s. They were commercialized in the 1970s (ELF ANTAR Molygraphite) and are today still available (Liqui Moly MoS2 10 W-40). Main disadvantage of molybdenum disulfide is anthracite black color, so oil treated with it is hard to distinguish from a soot filled engine oil with metal shavings from spun crankshaft bearing. * In the 1980s and 1990s, additives with suspended
PTFE Polytetrafluoroethylene (PTFE) is a synthetic fluoropolymer of tetrafluoroethylene that has numerous applications. It is one of the best-known and widely applied PFAS. The commonly known brand name of PTFE-based composition is Teflon by Chem ...
particles were available, e.g., "Slick50", to consumers to increase motor oil's ability to coat and protect metal surfaces. There is controversy as to the actual effectiveness of these products, as they can coagulate and clog the oil filter and tiny oil passages in the engine. It is supposed to work under boundary lubricating conditions, which good engine designs tend to avoid anyway. Also, Teflon alone has little to no ability to firmly stick on a sheared surface, unlike molybdenum disulfide, for example. * Many patents proposed use perfluoropolymers to reduce friction between metal parts, such as PTFE (Teflon), or micronized PTFE. However, the application obstacle of PTFE is insolubility in lubricant oils. Their application is questionable and depends mainly on the engine designone that can not maintain reasonable lubricating conditions might benefit, while properly designed engine with oil film thick enough would not see any difference. PTFE is a very soft material, thus its friction coefficient becomes worse than that of hardened steel-to-steel mating surfaces under common loads. PTFE is used in composition of sliding bearings where it improves lubrication under relatively light load until the oil pressure builds up to full hydrodynamic lubricating conditions. Some
molybdenum disulfide Molybdenum disulfide (or moly) is an inorganic compound composed of molybdenum and sulfur. Its chemical formula is . The compound is classified as a transition metal dichalcogenide. It is a silvery black solid that occurs as the mineral molybdeni ...
containing oils may be unsuitable for motorcycles which share
wet clutch A clutch is a mechanical device that engages and disengages power transmission, especially from a drive shaft to a driven shaft. In the simplest application, clutches connect and disconnect two rotating shafts (drive shafts or line shafts) ...
lubrication with the engine.


Environmental effects

Due to its chemical composition, worldwide dispersion and effects on the environment, used motor oil is considered a serious environmental problem. Most current motor-oil lubricants contain petroleum base stocks, which are toxic to the environment and difficult to dispose of after use. Over 40% of the pollution in America's waterways is from used motor oil. Used oil is considered the largest source of oil pollution in the U.S. harbors and waterways, at per year, mostly from improper disposal. By far the greatest cause of motor-oil pollution in oceans comes from drains and urban street-runoff, much of it caused by improper disposal of engine oil. of used oil can generate a slick on surface water, threatening fish, waterfowl and other aquatic life. According to the U.S. EPA, films of oil on the surface of water prevent the replenishment of dissolved oxygen, impair photosynthetic processes, and block sunlight. Toxic effects of used oil on freshwater and marine organisms vary, but significant long-term effects have been found at concentrations of 310 ppm in several freshwater fish species and as low as 1 ppm in marine life forms. Motor oil can have an incredibly detrimental effect on the environment, particularly to plants that depend on healthy soil to grow. There are three main ways that motor oil affects plants: * contaminating water supplies * contaminating soil * poisoning plants Used motor-oil dumped on land reduces soil productivity. Improperly disposed used oil ends up in landfills, sewers, backyards, or
storm drains A storm drain, storm sewer (United Kingdom, U.S. and Canada), surface water drain/sewer (United Kingdom), or stormwater drain (Australia and New Zealand) is infrastructure designed to drain excess rain and ground water from impervious surfaces ...
where soil, groundwater and drinking water may become contaminated.


Synthetic oils

Synthetic lubricants were first synthesized, or man-made, in significant quantities as replacements for mineral lubricants (and fuels) by German scientists in the late 1930s and early 1940s because of their lack of sufficient quantities of crude for their (primarily military) needs. A significant factor in its gain in popularity was the ability of synthetic-based lubricants to remain fluid in the sub-zero temperatures of the Eastern front in wintertime, temperatures which caused petroleum-based lubricants to solidify owing to their higher wax content. The use of synthetic lubricants widened through the 1950s and 1960s owing to a property at the other end of the temperature spectrum – the ability to lubricate aviation engines at high temperatures that caused mineral-based lubricants to break down. In the mid-1970s, synthetic motor oils were formulated and commercially applied for the first time in automotive applications. The same SAE system for designating motor oil
viscosity The viscosity of a fluid is a measure of its resistance to deformation at a given rate. For liquids, it corresponds to the informal concept of "thickness": for example, syrup has a higher viscosity than water. Viscosity quantifies the inte ...
also applies to
synthetic oil Synthetic oil is a lubricant consisting of chemical compounds that are artificially modified or synthesised. Synthetic lubricants can be manufactured using chemically modified petroleum components rather than whole crude oil, but can also be sy ...
s. Synthetic oils are derived from either Group III, Group IV, or some Group V bases. Synthetics include classes of lubricants like synthetic
esters In chemistry, an ester is a compound derived from an oxoacid (organic or inorganic) in which at least one hydroxyl group () is replaced by an alkoxy group (), as in the substitution reaction of a carboxylic acid and an alcohol. Glycerides are ...
(Group V) as well as "others" like GTL (methane gas-to-liquid) (Group III +) and polyalpha-olefins (Group IV). Higher purity and therefore better property control theoretically means synthetic oil has better mechanical properties at extremes of high and low temperatures. The molecules are made large and "soft" enough to retain good viscosity at higher temperatures, yet branched molecular structures interfere with solidification and therefore allow flow at lower temperatures. Thus, although the viscosity still decreases as temperature increases, these synthetic motor oils have a higher viscosity index over the traditional petroleum base. Their specially designed properties allow a wider temperature range at higher and lower temperatures and often include a lower pour point. With their improved viscosity index, synthetic oils need lower levels of viscosity index improvers, which are the oil components most vulnerable to thermal and mechanical degradation as the oil ages, and thus they do not degrade as quickly as traditional motor oils. However, they still fill up with particulate matter, although the matter better suspends within the oil, and the oil filter still fills and clogs up over time. So periodic oil and filter changes should still be done with synthetic oil, but some synthetic oil suppliers suggest that the intervals between oil changes can be longer, sometimes as long as primarily due to reduced degradation by oxidation. Tests show that fully synthetic oil is superior in extreme service conditions to conventional oil, and may perform better for longer under standard conditions. But in the vast majority of vehicle applications, mineral oil-based lubricants, fortified with additives and with the benefit of over a century of development, continue to be the predominant lubricant for most internal combustion engine applications.


Bio-based oils

Bio-based oils existed prior to the development of petroleum-based oils in the 19th century. They have become the subject of renewed interest with the advent of bio-fuels and the push for green products. The development of canola-based motor oils began in 1996 in order to pursue environmentally friendly products. Purdue University has funded a project to develop and test such oils. Test results indicate satisfactory performance from the oils tested. A review on the status of bio-based motor oils and base oils globally, as well as in the U.S, shows how bio-based lubricants show promise in augmenting the current petroleum-based supply of lubricating materials, as well as replacing it in many cases. The USDA National Center for Agricultural Utilization Research developed an Estolide lubricant technology made from vegetable and animal oils. Estolides have shown great promise in a wide range of applications, including engine lubricants. Working with the USDA, a California-based company Biosynthetic Technologies has developed a high-performance "drop-in" biosynthetic oil using Estolide technology for use in motor oils and industrial lubricants. This biosynthetic oil American Petroleum Institute (API) has the potential to greatly reduce environmental challenges associated with petroleum. Independent testing not only shows biosynthetic oils to be among the highest-rated products for protecting engines and machinery; they are also bio-based, biodegradable, non-toxic and do not bioaccumulate in marine organisms. Also, motor oils and lubricants formulated with biosynthetic base oils can be recycled and re-refined with petroleum-based oils. The U.S.-based company Green Earth Technologies manufactures a bio-based motor oil, called G-Oil, made from animal oils.


Future

A new process to break down
polyethylene Polyethylene or polythene (abbreviated PE; IUPAC name polyethene or poly(methylene)) is the most commonly produced plastic. It is a polymer, primarily used for packaging (plastic bags, plastic films, geomembranes and containers including ...
, a common plastic product found in many consumer containers, converts it into a paraffin-like wax with the correct molecular properties for conversion into a lubricant, avoiding the expensive
Fischer–Tropsch process The Fischer–Tropsch process is a collection of chemical reactions that converts a mixture of carbon monoxide and hydrogen, known as syngas, into liquid hydrocarbons. These reactions occur in the presence of metal catalysts, typically at temperatu ...
. The plastic is melted and then pumped into a furnace. The heat of the furnace breaks down the molecular chains of polyethylene into wax. Finally, the wax is subjected to a
catalytic Catalysis () is the process of increasing the rate of a chemical reaction by adding a substance known as a catalyst (). Catalysts are not consumed in the reaction and remain unchanged after it. If the reaction is rapid and the catalyst recycl ...
process that alters the wax's molecular structure, leaving a clear oil. Biodegradable motor oils based on esters or hydrocarbon-ester blends appeared in the 1990s followed by formulations beginning in 2000 which respond to the bio-no-tox-criteria of the European preparations directive (EC/1999/45). This means, that they not only are biodegradable according to OECD 301x test methods, but also the aquatic toxicities (fish, algae, daphnia) are each above 100 mg/L. Another class of base oils suited for engine oil are the polyalkylene glycols. They offer zero-ash, bio-no-tox properties, and lean burn characteristics.


Re-refined motor oil

The oil in a motor oil product does break down and burns as it is used in an engineit also gets contaminated with particles and chemicals that make it a less effective lubricant. Re-refining cleans the contaminants and used additives out of the dirty oil. From there, this clean "base stock" is blended with some virgin base stock and a new additives package to make a finished lubricant product that can be just as effective as lubricants made with all-virgin oil. The
United States Environmental Protection Agency The Environmental Protection Agency (EPA) is an independent executive agency of the United States federal government tasked with environmental protection matters. President Richard Nixon proposed the establishment of EPA on July 9, 1970; it ...
(EPA) defines re-refined products as containing at least 25% re-refined base stock, but other standards are significantly higher. The California State public contract code defines a re-refined motor oil as one that contains at least 70% re-refined base stock.


Packaging

Motor oils were sold at retail in
glass bottle A glass bottle is a bottle made from glass. Glass bottles can vary in size considerably, but are most commonly found in sizes ranging between about 200 millilitres and 1.5 litres. Common uses for glass bottles include food condiments, soda, liq ...
s, metal cans, and metal-cardboard cans, before the advent of the current
polyethylene Polyethylene or polythene (abbreviated PE; IUPAC name polyethene or poly(methylene)) is the most commonly produced plastic. It is a polymer, primarily used for packaging (plastic bags, plastic films, geomembranes and containers including ...
plastic bottle A plastic bottle is a bottle constructed from high-density or low density plastic. Plastic bottles are typically used to store liquids such as water, soft drinks, motor oil, cooking oil, medicine, shampoo, milk, and ink. The size ranges from ...
, which began to appear in the early 1980s. Reusable spouts were made separately from the cans; with a piercing point like that of a can opener, these spouts could be used to puncture the top of the can and to provide an easy way to pour the oil. Today, motor oil in the US is generally sold in bottles of and on a rarity in as well as in larger plastic containers ranging from approximately due to most small to mid-size engines requiring around of engine oil. In the rest of the world, it is most commonly available in 1L, 3L, 4L, and 5L retail packages. Distribution to larger users (such as drive-through oil change shops) is often in bulk, by tanker truck or in
drums A drum kit (also called a drum set, trap set, or simply drums) is a collection of drums, cymbals, and other auxiliary percussion instruments set up to be played by one person. The player (drummer) typically holds a pair of matching drumsticks ...
.


See also

* Waste oil


References


External links

*
Table of SAE and ISO viscosity gradings

Blog about motor oils

Measuring free radicals in used engine oil

Oil for high mileage
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Oil An oil is any nonpolar chemical substance that is composed primarily of hydrocarbons and is hydrophobic (does not mix with water) & lipophilic (mixes with other oils). Oils are usually flammable and surface active. Most oils are unsaturate ...
Engine lubrication systems Tribology