Antifreeze, or engine coolant, is a colored liquid that is mixed with water to help regulate your engine during extreme temperatures. As the temperature outside changes from hot to cold coolant is pumped throughout the engine block to maintain an even operating temperature. Antifreeze does more than just regulate temperature, however. Maintaining proper fluid levels also helps to prevent corrosion. Common antifreezes increase the boiling point of the liquid, allowing higher coolant temperature.
Because water has good properties as a coolant, water plus antifreeze is 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 bursting due to expansion when water freezes. Commercially, both the additive and the mixture are called antifreeze, depending on the context. 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.