The liquid substance added to a car’s cooling system is antifreeze. It is usually mixed with water to create engine coolant, which helps control temperature in both freezing and hot conditions.
Modern antifreeze is commonly based on ethylene glycol, although less-toxic propylene glycol is also used. Ethylene glycol solutions became available in 1926 and were marketed as “permanent antifreeze.” Unlike plain water, the mixture has a lower freezing point and a higher boiling point, helping prevent the coolant from freezing in winter or boiling away during engine operation.
Antifreeze does more than regulate temperature. Commercial coolant also contains additives that inhibit corrosion, reduce foaming, and protect metal components such as the radiator, water pump, and engine passages. The correct mixture matters: too much water reduces freeze protection, while too much antifreeze can reduce heat-transfer performance.
“Antifreeze” and “coolant” are often used interchangeably, but antifreeze is the concentrated product before it is mixed with water. Ethylene glycol is poisonous, so spills must be cleaned up and stored safely, especially around pets and children.