A pressure vent cap is used to allow a build-up between 95 kPa - 125 kPa (13.9 psi - 18 psi) in the cooling system. This pressure raises the boiling point of coolant to approximately 129°C (265°F) at sea level. Do not remove the cap to check the engine coolant level. Check the coolant visually at the see-through reservoir. Coolant should be added only to the reservoir.

Caution: 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 pressure cap while the engine is hot and pressure is high will cause the solution to boil instantaneously -- possibly with explosive force -- spewing the solution over the engine, fenders and the person removing the cap.

The pressure-type filler cap contains a blow-off (or pressure valve) and a vacuum (or atmospheric valve). The pressure valve is held against its seat by a calibrated spring and protects the radiator by relieving any internal pressure exceeding design specification.

The cap is designed to prevent accidental removal. The finger grips have been removed so that the cap is round in shape. It must be pushed downward before it can be removed. A rubber/asbestos gasket is added to the diaphragm spring at the top of the cap.