C 2500 Truck 2WD V8-5.7L VIN R (1997)
Radiator Cap: Description and Operation
OPERATION
The pressure-vent radiator cap allows a build-up of 103 kPa (15 psi) in the cooling system. This pressure raises the boiling point of the coolant to
about 129°C (265°F) at sea level. Do not remove the radiator cap to check the engine coolant level; check the coolant visually at the see-through
coolant recovery reservoir. Add coolant to the reservoir when the system cools.
WARNING: As long as there is pressure in the cooling system, the temperature can be considerably higher than the boiling temperature of
the solution in the radiator, without causing the solution to boil. Removal of the radiator cap while the engine is hot and the pressure is high
will cause the solution to boil instantaneously and possibly with explosive force, spewing the solution over the engine, fenders, and person
removing the cap. Under some conditions, the engine coolant is combustible.
Pressure Release
The radiator cap contains a blow off or pressure valve and a vacuum or atmospheric valve. The pressure valve is held against its seat by a spring of
predetermined strength. This protects the radiator by relieving internal pressure when it exceeds cooling system design limits. The vacuum valve is
held against its seat by a light spring which permits opening of the valve to relieve vacuum created in the system when it cools.
Cap Removal
The radiator cap is designed to discourage inadvertent removal. To safely remove the cap from the radiator, rotate the cap slowly counterclockwise
(do not press down) to the detent. Allow any pressure to release from the radiator. Press down on the cap, continue to rotate counterclockwise and
lift off the radiator.
Diaphragm Description
Under the diaphragm spring at the top of the cap is a gasket. Embossed on the cap is a caution against its being opened and arrows indicating the
proper closed position.
The seal of the filler cap and the operation of the pressure relief valve can be checked using a conventional cooling system testing kit.
