Ethylene glycol

Ethylene glycol, sometimes known by the trade name Prestone, is a cooling liquid developed for aircraft use that is now widely used in cars. It has several advantages over water in this role, including limited expansion compared to water, a higher boiling point and lower freezing point, and a much higher specific heat, meaning any unit carries more heat away from the engine than water.

When first introduced it created a minor revolution in aircraft design because its higher specific heat allowed for smaller radiators operating at higher temperatures. Prior to the widespead use of ethylene glycol, many companies tried to use evaporative cooling systems in which water under pressure is used to carry away more heat. Invariably these proved to be rather unreliable and easily damaged in combat because they took up large amounts of room on the plane, where they were easily hit by gunfire. Replacing these systems with ethylene glycol was easy, resulting in largely the same benefits (higher operating temperatures and smaller radiators) without complex plumbing.

Today the primary use is in cars, where it is used mainly for its low freezing point. It is so widespread in this role that it is more commonly known as antifreeze.