Antifreeze

Antifreeze is used in internal combustion engines and many other heat transfer applications, such as HVAC chillers and solar water heaters. The purpose of antifreeze is to prevent a rigid enclosure from undergoing physical stresses and catastrophic deformation due to the expansion that occurs when water turns to ice. Most antifreezes are chemical compounds made to be added to water to reduce the freezing point of the mixture below the lowest temperature that the system is likely to be exposed to. Either the additive or the mixture may be referred to as antifreeze, which enables competition between unmixed antifreeze (the additive) with premixed antifreeze (water + the additive) in common retail packaging.

In warm climates, these compounds also not only produce freezing point depression in the winter when mixed with water, they also raise the boiling point of water. These substances are properly referred to as both antifreeze and "anti-boil" when used for both properties.

Automotive use

The term engine coolant is widely used in the automotive industry, which covers its primary function of convective heat transfer. When used in an automotive context, corrosion inhibitors are also added to help protect vehicles' cooling systems, which often contain a range of electrochemically incompatible metals (aluminum, cast iron, copper, lead solder, etc.).

Antifreeze was developed to overcome the shortcomings of water as a heat transfer fluid. In most engines, freeze plugs are placed in the engine block which could protect the engine if no antifreeze was in the cooling system or if the ambient temperature dropped below the freezing point of the antifreeze. If the engine coolant gets too hot, it might boil while inside the engine, causing voids (pockets of steam), leading to the catastrophic failure of the engine. Using proper engine coolant and a pressurized coolant system can help alleviate both problems.

Some antifreezes can prevent freezing till -87° C.

Primary agents

Methanol

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, 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 liquid and is used as an antifreeze, solvent, fuel, and as a denaturant for ethyl alcohol. It is not very popular for machinery, but it can be found in automotive windshield washer fluid, de-icers, and gasoline additives to name a few.

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 for a wide variety of applications, including automobiles. Being ubiquitous, ethylene glycol has been ingested on occasion, causing ethylene glycol poisoning.

Poisoning

Ethylene glycol antifreeze has a sweet taste that can contribute to its accidental ingestion or its deliberate use as a murder weapon, as attributed by the many sensational media reports concerning it.^[1][2][3][4] Symptoms of antifreeze poisoning include severe diarrhea and vomiting; usually farther into the intoxication, signs of delirium, paranoia and intense hallucinations manifest.^[1][2][3][4] Antifreeze poisoning can be identified from the growth of calcium oxalate crystals in the kidneys.^[5] An embittering agent such as denatonium can be added to ethylene glycol to help discourage either accidental or deliberate poisoning.

Ethylene glycol is toxic to many animals, including cats and dogs,^[6] so waste antifreeze should be disposed properly or recycled. In some places, it is permitted to pour moderate amounts down the toilet, but there are also places where it can be taken for processing.^[7]

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, 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 lactic acid is formed.^[8][9] 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.

Besides cooling system breakdown, biological fouling also occurs. Once bacterial slime starts, the corrosion rate of the system increases. In systems 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 routinely.

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.^[10] A 1:1 dilution with water is usually used, resulting in a freezing point in the range of −35 °C to −40 °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% must be maintained to assure corrosion protection and optimum freezing prevention.

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

Organic acid technology

Certain cars are built with Organic Acid Technology (OAT) antifreeze (e.g., DEX-COOL^[11]), or with a Hybrid Organic Acid Technology (HOAT) formulation (e.g., Zerex G-05^[12]), both of which are claimed to have an extended service life of five years or 240,000 km (150,000 miles).

DEX-COOL specifically has caused controversy. Litigation has linked it with intake manifold gasket failures in GM's 3.1L and 3.4L engines, and with other failures in 3.8L & 4.3L engines. Class action lawsuits were registered in several states, and in Canada,^[13] 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.^[14] Late in March 2008, GM agreed to compensate complainants in the remaining 49 states.^[15]

There are rumors that mixing DEX-COOL with standard green (non-OAT) coolant causes a chemical reaction that produces sludge in the cooling system. According to the DEX-COOL manufacturer, however, "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."^[16]

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 permanently.^[17]

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 [4])

See also

• Colligative properties
• Radiator
• Internal combustion engine cooling
• Heater core
• Water cooling
• Air cooling
• Ice melt

References