Cap-Radiator Pressure: Description
All cooling systems are equipped with a pressure cap on the radiator. This cap releases pressure at some point within a range of 110-138 kPa (16-20 psi). The pressure relief point (in pounds) is engraved on top of the cap (3).
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 (4). This valve opens when system pressure reaches the release range of 110-138 kPa (16-20 psi).
A rubber gasket (2) seals the radiator filler neck. This is done to maintain vacuum during coolant cool-down and to prevent leakage when system is under pressure.