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Editor-In-Chief: C. Michael Gibson, M.S., M.D. [1]


Antifreeze is used in internal combustion engines, and for many other heat transfer applications, such as electronics cooling and chillers for HVAC. Compounds are added to water to reduce the freezing point of the mixture to below the lowest temperature that the system is likely to be exposed to, and to inhibit corrosion in cooling systems which often contain a range of electrochemically incompatible metals (aluminum, cast iron, copper, lead solder, etc.). The term "colligative agent" is to be preferred as, in warm climates, the benefit of these compounds is to increase the boiling point of the coolant, which should then be more properly referred to as "anti-boil", and as anti-freeze decreases and increases both properties, respectively, "colligative agent" more accurately describes the liquid. The term "engine coolant" is widely used in industry.



Methanol, also known as methyl alcohol, carbinol, wood alcohol, wood naphtha or wood spirits, is a chemical compound with chemical formula CH3OH (often abbreviated MeOH). It is the simplest alcohol, and is a light, volatile, colourless, flammable, poisonous liquid with a distinctive odor that is somewhat milder and sweeter than ethanol (ethyl alcohol). At room temperature it is a polar liquid and is used as an antifreeze, solvent, fuel, and as a denaturant for ethyl alcohol.

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 still used today. Ethylene glycol antifreezes are poisonous and should be kept away from any person or animal (children and especially cats) that might be tempted by its sweet taste. They form calcium oxalate crystals in the kidneys and can cause acute renal failure and death. All spills should be cleaned, or else an area in which it may be present should be kept inaccessible.

Should ingestion of antifreeze occur, ethanol (alcoholic beverages) can be administered until proper treatment can be started in order to slow the conversion of methanol to formaldehyde and formic acid which are the substances responsible for methanol's toxicity. In practice, ethanol can be administered intravenously by doctors to counter ethylene glycol and methanol poisoning, but now that another antidote is available (fomepizole), its popularity for this application is greatly in decline. [1]

In order to prevent ingestion, bittering agent (denatonium benzoate) is usually added to engine coolant to make it taste unpleasant. In the United States, there is legislation before Congress (H.R.2567/S.1110) that would make the use of a bittering agent mandatory.

Propylene glycol

File:Propylene glycol chemical structure.png
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, as well as numerous other settings. It is also used in food, medicines, and cosmetics, often as a binding agent. Propylene glycol is "generally recognized as safe" by the Food and Drug Administration (FDA) for use in food. However, propylene glycol-based antifreeze should not be considered safe for consumption. In the event of accidental ingestion, emergency medical services should be contacted immediately.

Propylene Glycol oxidizes when exposed to air and heat. When this occurs, organic acids are formed viz. Glycolic acid, Glyoxalic acid, Formic acid, Carbonic acid & Oxalic acid. If not properly inhibited, this fluid can be very corrosive. Protodin is added to Propylene Glycol to act as a buffer, preventing low pH attack on the system metals. It forms a protective skin inside the tank and pipelines which helps to prevent acid attack that cause corrosion.

Beside cooling system breakdown, biological fouling also occurs. Once bacterial slime starts the corrosion rate of the system increases. In system where a glycol solution is maintained on a continuous basis, regular monitoring of freeze protection, pH, specific gravity, inhibitor level, color and biological contamination should be checked on routine basis.

Propylene glycol should be replaced when it turns reddish in color.

Other developments

Most commercial antifreeze formulations include corrosion inhibiting compounds, and a colored dye (commonly a green, red or blue fluorescent) to aid in identification. A 1:1 dilution with water is usually used, resulting in a freezing point of approximately −40 °C. In warmer areas weaker dilutions are used.

Glycol antifreeze solutions should generally be replaced with fresh mixture every two years.

In the 1980s, inventor Jack Evans discovered the advantages of using a waterless coolant. His final formulation is a mixture propylene glycol. This coolant has a high boiling point of 188 °C (370 °F) and is not corrosive, solving many of water's problems including freezing. [2]

Organic acid technology

Certain cars are built with Organic Acid Technology (OAT) antifreeze (e.g., DEX-COOL [2]), which is claimed to have an extended service life of five years or 240,000 km (150,000 miles)[3].

According to the DEX-COOL manufacturer, "mixing a 'green' 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."[4]

DEX-COOL specifically has caused controversy. [5] It is casually linked with intake manifold gasket failures in GM's 3.1L and 3.4L and with other failures in 4.3L engines. Class action lawsuits were registered in several states, and in Canada,[6] 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. [7] Late in March 2008, GM agreed to compensate complainants in the remaining 49 states.[8]

Typically OAT antifreeze contains a red or pink dye to differentiate it from the conventional glycol-based coolants (blue or green). 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.

Effects on the human body

Anti-freeze turns to acid in the body and drinking just a small amount could be fatal. Nerve endings and blood vessels would be destroyed and tissue in the kidneys, brain and liver severely affected. Blindness and deafness can result and the nervous system comes under attack, leading to violent spasms in the limbs.

Famous Poisoning Cases

In a case in April 2005, Kate Knight of Stoke-On-Trent, Staffordshire, carried out a plan to poison and kill her husband Lee Knight, after learning she would gain over UK£100,000 from his employers JCB after his death. It is believed her motive for carrying out such an act was to pay off debts of thousands of pounds. Mr Knight had his food contaminated by antifreeze and subsequently came close to death. Mr Knight remained in a coma for 16 weeks and eventually managed to pull through. Despite this, he was left with brain damage, kidney failure, blindness, and deafness. Kate Knight was found guilty of his attempted murder and was jailed for 30 years in February 2008. Mr Knight has since spoken openly about his relationship with her and how he is coping today. His neighbour said he is not the same person but has a good sense of humour, recalling how he laughed about waking up well on frosty mornings. Others close to him have said he is being 'strong' and 'doing well'.


  1. Keyes, Daniel C. (2005). "Toxicity, Ethylene Glycol". eMedicine. Retrieved 2007-02-13.
  3. Forward - DEX-COOL 2007
  4. MACS 2001: GM and Texaco “Bare All” about DEX-COOL
  5. Forward - DEX-COOL 2007
  7. Tentative Settlement of GM DEX-COOL Class Action Suit

Further reading

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