Radiator Cap: Description and Operation

DESCRIPTION
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 125°C (257°F) at sea level.

NOTE:
^ 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.

Cap Alignment Arrows:

Pressure Valve
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. 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.