An antifreeze is an additive which lowers the freezing point of a
water-based liquid and increases its boiling point. An antifreeze
mixture is used to achieve freezing-point depression for cold
environments and also achieves boiling-point elevation ("anti-boil")
to allow higher coolant temperature. Freezing and boiling points are
colligative properties of a solution, which depend on the
concentration of the dissolved substance.
Because water has good properties as a coolant, water plus antifreeze
is used in internal combustion engines and other heat transfer
applications, such as
HVAC chillers and solar water heaters. The
purpose of antifreeze is to prevent a rigid enclosure from bursting
due to expansion when water freezes. Commercially, both the additive
(pure concentrate) and the mixture (diluted solution) are called
antifreeze, depending on the context. Careful selection of an
antifreeze can enable a wide temperature range in which the mixture
remains in the liquid phase, which is critical to efficient heat
transfer and the proper functioning of heat exchangers.
Salts are frequently used for de-icing, but salt solutions are not
used for cooling systems because they can cause severe corrosion to
metals. Instead, non-corrosive antifreezes are commonly used for
critical de-icing, such as for aircraft wings.
Automotive and internal combustion engine use
2 Other uses
3 Primary agents
3.2 Ethylene glycol
3.3 Propylene glycol
4 Measuring the freeze point
5.2 Traditional inhibitors
5.3 Organic acid technology
5.4 Hybrid organic acid technology
7 See also
Automotive and internal combustion engine use
Fluorescent green-dyed antifreeze is visible in the radiator header
tank when car radiator cap is removed
Most automotive engines are "water"-cooled to remove waste heat,
although the "water" is actually antifreeze/water mixture and not
plain water. The term engine coolant is widely used in the automotive
industry, which covers its primary function of convective heat
transfer for internal combustion engines. When used in an automotive
context, corrosion inhibitors are added to help protect vehicles'
radiators, which often contain a range of electrochemically
incompatible metals (aluminum, cast iron, copper, brass, solder, et
Water pump seal lubricant is also added.
Antifreeze was developed to overcome the shortcomings of water as a
heat transfer fluid. In some engines freeze plugs (engine block
expansion plugs) are placed in areas of the engine block where coolant
flows in order to protect the engine from freeze damage[citation
needed] if the ambient temperature drops below the freezing point of
the antifreeze/water mixture. These should not be confused with core
plugs, whose purpose is to allow removal of sand used in the casting
process of engine blocks (core plugs will be pushed out if the coolant
freezes, though, assuming that they adjoin the coolant passages, which
is not always the case).
On the other hand, if the engine coolant gets too hot, it might boil
while inside the engine, causing voids (pockets of steam), leading to
localized hot spots and the catastrophic failure of the engine. If
plain water were to be used as an engine coolant, it would promote
galvanic corrosion. Proper engine coolant and a pressurized coolant
system can help obviate the problems which make plain water
incompatible with automotive engines. With proper antifreeze, a wide
temperature range can be tolerated by the engine coolant, such as
−34 °F (−37 °C) to +265 °F (129 °C) for
50% (by volume) propylene glycol diluted with water and a 15 psi
pressurized coolant system.
Early engine coolant antifreeze was methanol (methyl alcohol).
Methanol was widely used in windshield fluids, however, in Europe, due
to new REACH legislation, the use of methanol in windshield fluids is
limited to 5% and in the near future will be further reduced to 3%.
As radiator caps were vented, not sealed, the methanol was lost to
evaporation, requiring frequent replenishment to avoid freezing of the
Methanol also accelerates corrosion of the metals, especially
aluminum, used in the engine and cooling systems.
Ethylene glycol was
developed, and soon[when?] replaced methanol as an engine cooling
system antifreeze. It has a very low volatility compared to methanol
and to water. Before the 1950s, coolant systems were unpressurized and
the engine was often cooler than modern automotive engines. By
pressurizing the coolant system with a radiator cap, the boiling point
of the fluid is increased, permitting higher engine temperatures and
better fuel efficiency. Pressurized systems do not appreciably change
the freezing point. Later propylene glycol was introduced due to its
The most common water-based antifreeze solutions used in electronics
cooling are mixtures of water and either ethylene glycol (EGW) or
propylene glycol (PGW). The use of ethylene glycol has a longer
history, especially in the automotive industry. However, EGW solutions
formulated for the automotive industry often have silicate based rust
inhibitors that can coat and/or clog heat exchanger surfaces. Ethylene
glycol is listed as a toxic chemical requiring care in handling and
Ethylene glycol has desirable thermal properties, including a high
boiling point, low freezing point, stability over a wide range of
temperatures, and high specific heat and thermal conductivity. It also
has a low viscosity and, therefore, reduced pumping requirements.
Although EGW has more desirable physical properties than PGW, the
latter coolant is used in applications where toxicity might be a
concern. PGW is generally recognized as safe for use in food or food
processing applications, and can also be used in enclosed spaces.
Similar mixtures are commonly used in
HVAC and industrial heating or
cooling systems as a high-capacity heat transfer medium. Many
formulations have corrosion inhibitors, and it is expected that these
chemicals will be replenished (manually or under automatic control) to
keep expensive piping and equipment from corroding.
Most antifreeze is made by mixing distilled water with additives and a
base product - MEG (Mono ethylene glycol) or MPG (Mono propylene
Main article: Methanol
Methanol (also known as methyl alcohol, carbinol, wood alcohol, wood
naphtha or wood spirits) is a chemical compound with chemical formula
CH3OH. It is the simplest alcohol, and is a light, volatile,
colorless, flammable, poisonous liquid with a distinctive odor that is
somewhat milder and sweeter than ethanol (ethyl alcohol). At room
temperature, it is a polar solvent and is used as an antifreeze,
solvent, fuel, and as a denaturant for ethyl alcohol. It is not
popular for machinery, but may be found in automotive windshield
washer fluid, de-icers, and gasoline additives.
Main article: Ethylene glycol
Ethylene glycol solutions became available in 1926 and were marketed
as "permanent antifreeze" since the higher boiling points provided
advantages for summertime use as well as during cold weather. They are
used today for a variety of applications, including automobiles, but
gradually being replaced by propylene glycol due to its lower
When ethylene glycol is used in a system, it may become oxidized to
five organic acids (formic, oxalic, glycolic, glyoxalic and acetic
acid). Inhibited ethylene glycol antifreeze mixes are available, with
additives that buffer the pH and reserve alkalinity of the solution to
prevent oxidation of ethylene glycol and formation of these acids.
Nitrites, silicates, theodin, borates and azoles may also be used to
prevent corrosive attack on metal.
Ethylene glycol poisoning
Ethylene glycol is poisonous to humans and other animals, and
should be handled carefully and disposed of properly. Its sweet taste
can lead to accidental ingestion or allow its deliberate use as a
Ethylene glycol is difficult to detect in the
body, and causes symptoms—including intoxication, severe diarrhea,
and vomiting—that can be confused with other illnesses or
diseases. Its metabolism produces calcium oxalate, which
crystallizes in the brain, heart, lungs, and kidneys, damaging them;
depending on the level of exposure, accumulation of the poison in the
body can last weeks or months before causing death, but death by acute
kidney failure can result within 72 hours if the individual does not
receive appropriate medical treatment for the poisoning. Some
ethylene glycol antifreeze mixtures contain an embittering agent, such
as denatonium, to discourage accidental or deliberate consumption.
Propylene glycol is considerably less toxic than ethylene glycol and
may be labeled as "non-toxic antifreeze". It is used as antifreeze
where ethylene glycol would be inappropriate, such as in
food-processing systems or in water pipes in homes where incidental
ingestion may be possible. For example, the FDA allows propylene
glycol to be added to a large number of processed foods, including ice
cream, frozen custard, salad dressings, and baked goods, and it is
commonly used as the main ingredient in the "e-liquid" used in
Propylene glycol oxidizes when exposed to air and heat, forming lactic
acid. If not properly inhibited, this fluid can be very
corrosive, so pH buffering agents such as dipotassium
phosphate and potassium bicarbonate are often added to propylene
glycol, to prevent acidic corrosion of metal components. Pre-inhibited
propylene glycol solutions can also be used instead of pure propylene
glycol to prevent corrosion.
Besides cooling system corrosion, biological fouling also occurs. Once
bacterial slime starts to grow, the corrosion rate of the system
increases. Maintenance of systems using glycol solution includes
regular monitoring of freeze protection, pH, specific gravity,
inhibitor level, color, and biological contamination.
Propylene glycol should be replaced when it turns a reddish color.
When an aqueous solution of propylene glycol in a cooling or heating
system develops a reddish or black color, this indicates that iron in
the system is corroding significantly. In the absence of inhibitors,
propylene glycol can react with oxygen and metal ions, generating
various compounds including organic acids (e.g., formic, oxalic,
acetic). These acids accelerate the corrosion of metals in the
Once used for automotive antifreeze, glycerol has the advantage of
being non-toxic, withstands relatively high temperatures, and is
Like ethylene glycol and propylene glycol, glycerol is a non-ionic
kosmotrope that forms strong hydrogen bonds with water molecules,
competing with water-water hydrogen bonds. This disrupts the crystal
lattice formation of ice unless the temperature is significantly
lowered. The minimum freezing point temperature is at about
−36 °F / −37.8 °C corresponding to 60–70% glycerol
Glycerol was historically used as an antifreeze for automotive
applications before being replaced by ethylene glycol, which has a
lower freezing point. While the minimum freezing point of a
glycerol-water mixture is higher than an ethylene glycol-water
mixture, glycerol is not toxic and is being re-examined for use in
Glycerol is mandated for use as an
antifreeze in many sprinkler systems.
In the laboratory, glycerol is a common component of solvents for
enzymatic reagents stored at temperatures below 0 °C due to the
depression of the freezing temperature of solutions with high
concentrations of glycerol. It is also used as a cryoprotectant where
the glycerol is dissolved in water to reduce damage by ice crystals to
laboratory organisms that are stored in frozen solutions, such as
bacteria, nematodes, and mammalian embryos.
Measuring the freeze point
Once antifreeze has been mixed with water and put into use, it
periodically needs to be maintained. If engine coolant leaks, boils,
or if the cooling system needs to be drained and refilled, the
antifreeze's freeze protection will need to be considered. In other
cases a vehicle may need to be operated in a colder environment,
requiring more antifreeze and less water. Three methods are commonly
employed to determine the freeze point of the solution:
Specific gravity—(using a hydrometer test strip or some sort of
Refractometer—which measures the refractive index of the antifreeze
solution and translates it into freeze point, and
Test strips—specialized, disposable indicators made for this
Although ethylene glycol hydrometers are widely available and
mass-marketed for antifreeze testing, they give false readings at high
temperatures because specific gravity changes with temperature.
Propylene glycol solutions cannot be tested using specific gravity
because of ambiguous results (40% and 100% solutions have the same
Most commercial antifreeze formulations include corrosion inhibiting
compounds, and a colored dye (commonly a fluorescent green, red,
orange, yellow, or blue) to aid in identification. A 1:1 dilution
with water is usually used, resulting in a freezing point of about
−34 °F (−37 °C), depending on the formulation. In
warmer or colder areas, weaker or stronger dilutions are used,
respectively, but a range of 40%/60% to 60%/40% is frequently
specified to ensure corrosion protection, and 70%/30% for maximum
freeze prevention down to −84 °F (−64 °C).
In the absence of leaks, antifreeze chemicals such as ethylene glycol
or propylene glycol may retain their basic properties indefinitely. By
contrast, corrosion inhibitors are gradually used up, and must be
replenished from time to time. Larger systems (such as
are often monitored by specialist firms which take responsibility for
adding corrosion inhibitors and regulating coolant composition. For
simplicity, most automotive manufacturers recommend periodic complete
replacement of engine coolant, to simultaneously renew corrosion
inhibitors and remove accumulated contaminants.
Traditionally, there were two major corrosion inhibitors used in
vehicles: silicates and phosphates. American made vehicles
traditionally used both silicates and phosphates. European makes
contain silicates and other inhibitors, but no phosphates.
Japanese makes traditionally use phosphates and other inhibitors, but
Organic acid technology
Certain cars are built with organic acid technology (OAT) antifreeze
(e.g., DEX-COOL), or with a hybrid organic acid technology (HOAT)
formulation (e.g., Zerex G-05), both of which are claimed to have
an extended service life of five years or 240,000 km
DEX-COOL specifically has caused controversy. Litigation has linked it
with intake manifold gasket failures in General Motors' (GM's) 3.1L
and 3.4L engines, and with other failures in 3.8L and 4.3L engines.
One of the anti-corrosion components presented as sodium or Potassium
2-ethylhexanoate and ethylhexanoic acid is incompatible with nylon 6,6
and silicone rubber, and is a known plasticizer.
Class action lawsuits
were registered in several states, and in Canada, to address some
of these claims. The first of these to reach a decision was in
Missouri, where a settlement was announced early in December 2007.
Late in March 2008, GM agreed to compensate complainants in the
remaining 49 states. GM (Motors Liquidation Company) filed for
bankruptcy in 2009, which tied up the outstanding claims until a court
determines who gets paid.
According to the DEX-COOL manufacturer, "mixing a 'green' [non-OAT]
coolant with DEX-COOL reduces the batch's change interval to 2 years
or 30,000 miles, but will otherwise cause no damage to the
engine". DEX-COOL antifreeze uses two inhibitors: sebacate and
2-EHA (2-ethylhexanoic acid), the latter which works well with the
hard water found in the United States, but is a plasticizer that can
cause gaskets to leak.
According to internal GM documents, the ultimate
culprit appears to be operating vehicles for long periods of time with
low coolant levels. The low coolant is caused by pressure caps that
fail in the open position. (The new caps and recovery bottles were
introduced at the same time as DEX-COOL). This exposes hot engine
components to air and vapors, causing corrosion and contamination of
the coolant with iron oxide particles, which in turn can aggravate the
pressure cap problem as contamination holds the caps open
Honda and Toyota's new extended life coolant use OAT with sebacate,
but without the 2-EHA. Some added phosphates provide protection while
the OAT builds up. Honda specifically excludes 2-EHA from their
Typically, OAT antifreeze contains an orange dye to differentiate it
from the conventional glycol-based coolants (green or yellow). Some of
the newer OAT coolants claim to be compatible with all types of OAT
and glycol-based coolants; these are typically green or yellow in
color (for a table of colors, see).
Hybrid organic acid technology
HOAT coolants typically mix an OAT with a traditional inhibitor, such
as silicates or phosphates.
G05 is a low-silicate, phosphate free formula that includes the
All automotive antifreeze formulations, including the newer organic
acid (OAT antifreeze) formulations, are environmentally hazardous
because of the blend of additives (around 5%), including lubricants,
buffers and corrosion inhibitors. Because the additives in
antifreeze are proprietary, the safety data sheets (SDS) provided by
the manufacturer list only those compounds which are considered to be
significant safety hazards when used in accordance with the
manufacturer's recommendations. Common additives include sodium
silicate, disodium phosphate, sodium molybdate, sodium borate,
denatonium benzoate and dextrin (hydroxyethyl starch). Disodium
fluorescein dyes are added to antifreeze to help trace the source of
leaks, and as an identifier since some different formulations are
Automotive antifreeze has a characteristic odor due to the additive
tolytriazole, a corrosion inhibitor. The unpleasant odor in industrial
use tolytriazole comes from impurities in the product that are formed
from the toluidine isomers (ortho-, meta- and para-toluidine) and
meta-diamino toluene which are side-products in the manufacture of
tolytriazole. These side-products are highly reactive and produce
volatile aromatic amines which are responsible for the unpleasant
Internal combustion engine
Internal combustion engine cooling
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Lead Replacement Petrol
Compressed natural gas
Racing fuel (Tetraethyllead)
Methyl tert-butyl ether
Automatic transmission fluid
Windshield washer fluid
Pay at the pump
Part of the Automobile series
Cylinder head (crossflow, reverse-flow)
Starter ring gear
Pneumatic valve springs
Variable valve timing
Cold air intake
Electronic throttle control
Naturally aspirated engine
Short ram air intake
Variable-length intake manifold
Warm air intake
Gasoline direct injection
Stratified charge engine
Turbo fuel stratified injection
High tension leads
Electrics and engine
Air–fuel ratio meter
Automatic Performance Control
Car battery (lead–acid battery)
Crankshaft position sensor
Drive by wire
Electronic control unit
Engine control unit
Engine coolant temperature sensor
Idle air control actuator
Mass flow sensor
Throttle position sensor
Automobile emissions control
Diesel particulate filter
Antifreeze (ethylene glycol)
Viscous fan (fan clutch)
Cylinder head porting