Wrangler 4WD L4-150 2.5L VIN P MFI (1998)
Radiator Cap: Description and Operation
Radiator Pressure Cap
All radiators are equipped with a pressure cap. This cap releases pressure at some point within a range of 83-124 kPa (12-18 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 springloaded pressure relief valve. This valve opens when system pressure reaches the release range of
83-124 kPa (12-18 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 coolant cools, it contracts and creates a vacuum in the 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.
