Antifreeze is a freeze preventive 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 undergoing catastrophic deformation due to expansion when water turns to ice. Antifreezes are chemical compounds added to water to reduce the freezing point of the mixture below the lowest temperature that the system is likely to encounter. Either the additive or the mixture may be referred to as antifreeze.

An antifreeze mixture achieves freezing point depression for a cold environment and also achieves boiling point elevation to enable higher liquid temperatures. This is described as the action of a colligative agent, which can properly be referred to as both antifreeze and "anti-boil" when used for both properties. 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.


Automotive and internal combustion engine use

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 (aluminium, cast iron, copper, brass, solder, et cetera). 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 are placed in areas of the engine block where coolant flows in order to protect the engine from freeze damage 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).

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.[1][2]

Early engine coolant antifreeze was methanol (methyl alcohol), still used in windshield washer fluid. As radiator caps were vented, not sealed, the methanol was lost to evaporation, requiring frequent replenishment to avoid freezing of the coolant. Methanol also accelerates corrosion of the metals, especially aluminium, used in the engine and cooling systems. Ethylene glycol was developed, and soon replaced methanol as an engine cooling system antifreeze. It has a very low volatility compared to methanol and to water.

Other uses

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. The use of PGW as a coolant is becoming more common primarily because it is environmentally friendly and non-toxic. Ethylene glycol is listed as a toxic chemical requiring care in handling and disposal.

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.

Primary agents

Most antifreeze is made by mixing distilled water with some kind of alcohol.


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.

Ethylene glycol

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.


Ethylene glycol is toxic to humans, as well as to other animals,[3] and should therefore be handled and disposed of properly. It has a sweet taste that can contribute to its accidental ingestion or its deliberate use as a murder weapon, as attributed by sensational media reports concerning it.[4][5][6][7] Such poisoning is difficult to identify without specialized testing, as it often mimics other illnesses, and various symptoms can result from such poisoning, including severe diarrhea and vomiting.[8][4][5][6][7] Some ethylene glycol antifreeze contains an embittering agent such as denatonium to help discourage either accidental or deliberate consumption.


Once used for automotive antifreeze, glycerol has the advantage of being non-toxic and could be used in the future for some applications.[9]

Propylene glycol

Propylene glycol

Propylene glycol, on the other hand, is considerably less toxic 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.

Propylene glycol oxidizes when exposed to air and heat, forming lactic acid.[10][11] If not properly inhibited, this fluid can be very corrosive,[citation needed] so pH buffering agents are often added to propylene glycol, to prevent acidic corrosion of metal components.

Besides cooling system breakdown, biological fouling also occurs. Once bacterial slime starts, 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.[why?]

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 radiator 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:[12]

  1. Specific gravity— (using a hydrometer or some sort of floating indicator),
  2. Refractometer— which uses the optical properties of the solution, and
  3. Test strips— specialized, disposable indicators made for this purpose.

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.[12] Propylene glycol solutions cannot be tested using specific gravity because of ambiguous results (40% and 100% solutions have the same specific gravity).[12]

Corrosion Inhibitors

Most commercial antifreeze formulations include corrosion inhibiting compounds, and a colored dye (commonly a green, red, orange, yellow, or blue fluorescent) to aid in identification.[13] 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).[2]

Traditional inhibitors

Traditionally, there were two major corrosion inhibitors used in vehicles: silicates and phosphates. American made vehicles traditionally used both silicates and phosphates.[14] European makes contain phosphates and other inhibitors, but no silicates.[14] Japanese makes traditionally use phosphates and other inhibitors, but no silicates. [14]

Organic acid technology

Certain cars are built with organic acid technology (OAT) antifreeze (e.g., DEX-COOL[15]), or with a hybrid organic acid technology (HOAT) formulation (e.g., Zerex G-05[16]), both of which are claimed to have an extended service life of five years or 240,000 km (150,000 mi).

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. 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.[17] Late in March 2008, GM agreed to compensate complainants in the remaining 49 states.[18] GM (Motors Liquidation Company) filed for bankruptcy in 2009, which tied up the outstanding claims until a court determines who gets paid.[19]

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."[20] 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 US, but is a plasticizer which can cause gaskets to leak.[14]

According to internal GM documents,[citation needed] 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 permanently.[21]

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.[14] Honda specifically excludes 2-EHA from their formulas.

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 [13])

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 benzoate inhibitor.[14]


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.[22] Because the additives in antifreeze are proprietary, the material safety data sheets (MSDS) 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, 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 incompatible.[13]

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.[23] These side-products are highly reactive and produce volatile aromatic amines which are responsible for the unpleasant odor.[24]

See also


  1. ^ Prestone Press Release
  2. ^ a b Peak Antifreeze chart
  3. ^ "Antifreeze Warning". The Cat Fanciers' Association, Inc.. Retrieved 2007-05-15. 
  4. ^ a b Nash, Alanna. "The Black Widow Killer: Two men. Two murders. Too many questions.". Reader's Digest. Retrieved 2009-04-26. 
  5. ^ a b Grinberg, Emanuella (2008-01-30). "Black Widow's' antifreeze murder trial to start". CNN. Retrieved 2009-04-26. 
  6. ^ a b Munro, Ian (2007-10-13). "Death by anti-freeze 'perfect murder'". The Age. Retrieved 2009-04-25. 
  7. ^ a b Angela Chambers and Jon Meyersohn (2009-04-23). "Exhumed Body Reveals Stacey Castor's First Husband 'Didn't Just Die': Exclusive Look Inside Anti-Freeze Murder Mystery; What Brought Two Men to Rest in Neighboring Graves". ABC. Retrieved 2009-04-25. 
  8. ^ Brent J (2001). "Current management of ethylene glycol poisoning". Drugs 61 (7): 979–88. doi:10.2165/00003495-200161070-00006. ISSN 0012-6667. PMID 11434452. 
  9. ^ Hudgens, R. Douglas; Hercamp, Richard D.; Francis, Jaime; Nyman, Dan A.; Bartoli, Yolanda (2007). doi:10.4271/2007-01-4000. 
  10. ^ Charles Loudon Bloxam (1873). Chemistry, inorganic and organic: with experiments (2 ed.). H.C. Lea. p. 587. 
  11. ^ Evaluation of Certain Food Additives and Contaminants (Technical Report Series). World Health Organization. p. 105. ISBN 92-4-120909-7. 
  12. ^ a b c Engine Cooling Testing: Why use a refractometer? posted 2/7/2001 by Michael Reimer
  13. ^ a b c Coolants Matrix 2003_5.xls. (PDF) . Retrieved on 2011-01-01.
  14. ^ a b c d e f [1] COOLANT CONFUSION: It's Not Easy Being Green... or Yellow or Orange or... . Retrieved on 2011-06-22.
  15. ^ Products: North America: Anti Freeze/Coolants. (2003-01-31). Retrieved on 2011-01-01.
  16. ^ [2][dead link]
  17. ^ Tentative Settlement of GM DEX-COOL Class Action Suit
  18. ^ DEX-COOL Litigation Website
  19. ^
  20. ^ MACS 2001: GM and Texaco “Bare All” about DEX-COOL. Retrieved on 2011-01-01.
  21. ^ Draft—DEX 2007, Part 3: Now It’s All Up To The Judges and Juries. Retrieved on 2011-01-01.
  22. ^ A safe and effective propylene glycol based capture liquid for fruit fly traps baited with synthetic lures – page 2|Florida Entomologist. Retrieved on 2011-01-01.
  23. ^ VOGT, P. F. 2005. Tolytriazole-myth and misconceptions. The Analyst 12: 1–3.
  24. ^ A safe and effective propylene glycol based capture liquid for fruit fly traps baited with synthetic lures; Florida Entomologist, June, 2008 by Donald B. Thomas

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