RAM 1500 Truck 4WD V8-5.9L VIN Z (2002)
Radiator Cap: Description and Operation
RADIATOR PRESSURE CAP
DESCRIPTION
All cooling systems are equipped with a pressure cap. For 5.9L engines, the pressure cap is located on top of the radiator outlet tank. For the
3.7L/4.7L engines, the pressure cap is located on top of the coolant degas container. The 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 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.
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. For the 5.9L engine, this causes the vacuum valve to open and coolant in the reserve/overflow container to be drawn
through the recovery hose connecting the filler neck and reserve/overflow container. If the vacuum valve is stuck shut, or the recovery hose is kinked,
radiator hoses will collapse on cool down.
For the 3.7L/4.7L engine, the vacuum valve will open and relieve the vacuum pressure in the cooling system.
