Cooling System Pressure Cap
DESCRIPTIONRadiators are equipped with a pressure cap, which releases pressure at some point within a range of 97 - 124 kPa (14 - 18 psi). The pressure relief point (in pounds) is engraved on top of 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.
A rubber gasket seals radiator filler neck to prevent leakage. This is done to keep system under pressure. It also maintains vacuum during coolant cool-down allowing coolant to return from reserve/ overflow tank.
OPERATION
The cap contains a spring-loaded pressure relief valve that opens when system pressure reaches release range of 97 - 124 kPa (14 - 18 psi).
A vent valve in the center of cap allows a small coolant flow through cap when coolant is below boiling temperature. The valve is completely closed when boiling point is reached. As the coolant cools, it contracts and creates a vacuum in the cooling system. This causes the vacuum valve to open and coolant in the reserve/overflow tank to be drawn through its connecting hose into radiator. If the vacuum valve is stuck shut, the radiator hoses will collapse on cool down.
Clean the vent valve.