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 ...

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 combus ...

s. They typically consist of

base oil Base oils are used to manufacture products including lubricating greases, motor oil and metal processing fluids. Different products require different compositions and properties in the oil. One of the most important factors is the liquid’s visco ...

s enhanced with various additives, particularly antiwear additives, 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 se ...

s, and, for multi-grade oils,

viscosity index improver 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 ...

s. 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 against each other. There are several types of friction: *Dry friction is a force that opposes the relative lateral motion of t ...

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 m ...

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

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 al ...

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 more ...

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 engine ...

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 crud ...

-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 ex ...

polyalphaolefins 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 ...

(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 ar ...

s for better dissolution of additives.

History

On 6 September 1866, American John Ellis founded the

Continuous Oil Refining Company Valvoline Inc. is an American manufacturer and distributor of Valvoline-brand automotive oil, additives, and lubricants. It also owns the Valvoline Instant Oil Change and Valvoline Express Care chains of car repair centers. , it is the second ...

. 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

used in

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 ...

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, cruising ...

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 lawn, grass surface to an even height. The height of the cut grass may be fixed by the design of the mower, ...

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 contexts ...

s, and many other machines. In engines, there are parts which move against each other, and the

between the parts wastes otherwise useful

power Power most often refers to: * Power (physics), meaning "rate of doing work" ** Engine power, the power put out by an engine ** Electric power * Power (social and political), the ability to influence people or events ** Abusive power Power may a ...

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 accele ...

into

. It also

s away those parts, which could lead to lower efficiency and degradation of the engine. Proper

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 Conductor or conduction may refer to: Music * Conductor (music), a person who leads a musical ensemble, such as an orchestra. * Conductor (album), ''Conductor'' (album), an album by indie rock band The Comas * Conduction, a type of structured f ...

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 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 cave ...

, 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. Motor oil refill with funnel

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 min ...

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 wel ...

, 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 d ...

at elevated