Coolant Duties
Coolant is a mixture of water and antifreeze. The antifreeze in the coolant (specifically, the ethylene glycol) prevents it from freezing and boiling. Like ice, frozen coolant would expand with great pressure and crack the engine block. The antifreeze also gives the coolant a higher boiling point than ordinary water. Additives in the antifreeze also prevent rust and scale buildup inside the cooling system; this permits efficient transfer of heat between the metal surfaces and the coolant. It also prevents such buildups from damaging the water pump. Finally, coolant acts as a lubricant for the water pump bearings and seals.