Radiator Cap: Description and Operation

DESCRIPTION





All radiators are equipped with a pressure cap. This cap releases pressure at some point within a range of 124 to 145 kPa (18 to 21 psi). The pressure relief point (in pounds) is engraved on top of the cap.
The cooling system will operate at pressures slightly above atmospheric pressure. This results in a higher coolant boiling point allowing increased radiator cooling capacity. The cap contains a spring loaded pressure relief valve. This valve opens when system pressure reaches the release range of 124 to 145 kPa (18 to 21 psi).
A rubber gasket seals the radiator filler neck. This is done to maintain vacuum during coolant cooldown and to prevent leakage when system is under pressure.

OPERATION
A vent valve in the center of the cap will remain shut as long as the cooling system is pressurized. As the coolant cools, it contracts and creates a vacuum in cooling system. This causes the vacuum valve to open and coolant in reserve/overflow tank to be drawn through connecting hose into radiator. If the vacuum valve is stuck shut, or overflow hose is kinked, radiator hoses will collapse on cooldown.