What is Antifreeze?

Michael Pollick
Michael Pollick

Antifreeze, also known as engine coolant, is a liquid substance that circulates through an internal combustion engine and draws off excessive heat. The two most common chemicals used for this are ethylene and propylene glycol, both of which have lower freezing points than water (32° Fahrenheit or 0° Celsius). This allows the chemicals to flow freely even under cold winter conditions. Antifreeze also has a higher boiling point than pure water, which makes it ideal for summer use as well.

Antifreeze, poured into the radiator, keeps an engine cool.
Antifreeze, poured into the radiator, keeps an engine cool.

Internal combustion engines generate a significant amount of heat as part of their normal operations. This heat is eventually transferred to the metallic and synthetic parts of the engine block, which in turn causes friction and expansion. Engine oils and lubricants may reduce the friction, but the heat still needs to dissipate away from the engine. This is where antifreeze enters the picture. A closed system of hoses and a water pump circulates either pure antifreeze or a mixture of it with water throughout the engine block.

A pet that ingests antifreeze should immediately be taken to the vet.
A pet that ingests antifreeze should immediately be taken to the vet.

The excessive heat is drawn away by the "heat sink" effect of the chemicals. By the time the antifreeze has passed through the entire engine block, it may be near the boiling point of water. This superheated liquid is pumped into a radiator placed in the front of the engine compartment. A combination of outside air and forced air from a fan help to reduce the temperature. The radiator itself has numerous chambers and channels that allow heat to pass through to the outside air as well. As the antifreeze reaches the other side of the radiator, it should be cool enough to re-enter the engine block and start the process all over again.

Not all antifreeze compounds are created equal. Some are intended for regions with extreme temperature variations, while other are formulated for summer months with higher heat ranges. There may also be variations in the ratio of water to antifreeze for optimal operations. Too little antifreeze can lead to boil-overs or a completely frozen radiator. Too much may not harm the car's operation, but it can be too expensive for drivers to use undiluted product all of the time. The chemicals are generally inexpensive, but occasionally there are sudden price spikes as demand rises and supplies run low.

One important thing to keep in mind is the poisonous nature of ethylene or propylene glycol. Antifreeze can smell sweet and look inviting to pets and small children. Drinking it can cause serious illness or even death, so containers should be kept in secured storage areas. If a pet ingests antifreeze, a veterinarian should be contacted immediately for emergency services. It's important to warn children not to drink it because, even if parents store it carefully, neighbors may not be so conscientious.

Engine coolant or antifreeze can be used to keep an engine operating at optimal temperatures.
Engine coolant or antifreeze can be used to keep an engine operating at optimal temperatures.
Michael Pollick
Michael Pollick

A regular wiseGEEK contributor, Michael enjoys doing research in order to satisfy his wide-ranging curiosity about a variety of arcane topics. Before becoming a professional writer, Michael worked as an English tutor, poet, voice-over artist, and DJ.

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Discussion Comments


@Anon56238: never pour anti-freeze down the sewer! It's deadly to aquatic life, just like dogs (like the article says).


does anti-freeze help break down bacteria when poured down the sewer? if this is not recommended then please give the reason and why.


help. I need a chart which will give the percentage of eth glycol antifreeze and the temperature to which it will protect down to before freezing. anyone know where I can obtain this kind of information? thanks


Antifreeze essentially works as a heat sink for the engine block, which means it absorbs excess heat and then allows it to dissipate in the numerous folds of the radiator. A mixture of antifreeze and water can indeed reach the boiling point, and it looks pretty dramatic when it does. However, the antifreeze generally circulates in hoses and chambers which are separate from the engine's essential parts like pistons and combustion chambers. Your engine is far more likely to be damaged if the engine oil level is too low or it breaks down from excessive heat. When that happens, piston rods could snap and the engine could seize up. Having boiling hot antifreeze is indicative of a dangerously overheated engine, but it doesn't necessarily indicate permanent engine damage.


Hello, I am concerned a little over a year, I hit a hard plastic cone on the freeway which I thought it had broke my 99 Nissan Altima antifreeze container. So for all this time, I never checked it. What I found out today is that, it was not broken, but the windshield container was. So I ran to the auto zone and filled it up using a 50/50 antifreeze. But I am worry about having neglected it for so long. What should I do? please get back with me.


while driving, a belt under my hood decided it wanted to snap. i had no power steering and my battery was dying fast. a friend did want to leave it on the road to he forced the steering till i got to a house. the antifreeze was boiling, i could hear the bubbling of it. turned off the truck and it started smoking from the right side. now when an engine over heats it come right from the center. did i completely ruin my truck by getting to the point of having my antifreeze start to boil?

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