Antifreeze coolant is one of the most vital fluids in your cars operation since it protects the engine from corrosion from boiling or freezing temperatures and helps transfer heat from the engine to the radiator While water could potentially serve the purpose of heat transferring most coolants only contain 2-4 percent water which is subject to freezing and boiling The main ingredient of coolant is glycol; usually ethylene glycol and the rest are additives which protect your cars inner workings against corrosion rust and pitting caused by air bubbles imploding in the cooling system