[SpudRider]

Radiator Cap

The radiator cap is a pressure relief valve. The engine cooling system is a closed system. As the engine transfers heat to the antifreeze the coolant expands, creating water pressure in the system. When the water pressure reaches 16 psi (1.1 Bar), the radiator cap protects the system by venting coolant into an overflow bottle to reduce excess pressure. At the same time the radiator cap maintains moderate pressure in the closed system to increase the boiling point of the coolant, and to prevent air voids from being introduced to the coolant. When the temperature of the coolant decreases, the pressure in the system also decreases. At this point the radiator cap allows coolant to be drawn from the overflow bottle back into the system.



The following video describes how a radiator cap operates.