Grand Cherokee 2WD V8-5.2L VIN Y (1998)
Radiator Cap: Description and Operation
All radiators are equipped with a pressure cap. This cap releases pressure at some point within a range of 97-to-124 kPa (14 to 18 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
97-to-124 kPa (14-to-18 psi)
A vent valve in the center of the cap allows a small coolant flow through the 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 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, radiator hoses will collapse on
cool-down.
A rubber gasket seals the radiator filler neck. This is done to maintain vacuum during coolant cool-down and to prevent leakage when system is under
pressure.