Caution: Do not remove the radiator cap while the cooling system is hot. Serious personal injury may result. Only remove the radiator cap from a cool engine.

A pressure-vent cap allows a build-up of 110 kPa (16 psi) in the cooling system. This pressure raises the boiling point of the coolant to about 125 ° C (257 ° F) at sea level. Do not remove the radiator in order to check the engine coolant level. Check the coolant visually at the see-through coolant reservoir. Add coolant to the reservoir only when the system cools.

The pressure/vent radiator cap contains a pressure valve and a vacuum valve. The pressure valve is held against its seat by a spring of predetermined strength. This spring protects the radiator by relieving internal pressure when it exceeds the cooling system's design limits. The vacuum valve is held against its seat by a spring that permits the valve to open to relieve the vacuum created in the system when it cools off. The vacuum might otherwise cause the radiator to collapse.

The radiator cap is designed to discourage inadvertent removal. In order to safely remove the cap, rotate it slowly counterclockwise, but do not press down, to the detent. Allow any pressure to relieve. Next, press down on the cap and continue to rotate it counterclockwise and lift it off.

Under the diaphragm spring at the top of the cap is a rubber gasket. Embossed on the cap is a caution against it being opened and arrows indicating the proper closed position.

The seal of the radiator cap and the operation of the pressure relief valve can be checked using a conventional cooling system test kit such as J 24460-01 or the equivalent.