A pressure-vent cap is used on the cross-flow radiator to allow a buildup of 103 kPa (15 psi) in the cooling system. This pressure raises the boiling point of coolant to approximately 125°C (262 °F) at sea level.
DO NOT REMOVE RADIATOR CAP TO CHECK ENGINE COOLANT LEVEL; CHECK COOLANT VISUALLY AT THE SEE-THROUGH COOLANT RESERVOIR. COOLANT SHOULD BE ADDED ONLY TO THE RESERVOIR.
The pressure-type radiator filler cap contains a blow off or pressure valve (Figure 2-52) and a vacuum or atmospheric valve (Figure 2-53).
The pressure valve is held against its seat by a spring of pre-determined strength which protects the radiator by relieving the pressure if an extreme case of internal pressure should exceed that for which the cooling system is designed.
A vacuum valve is used which permits opening of the valve to relieve vacuum created in the system when it cools off and which otherwise might cause the radiator to collapse. It also permits transfer of coolant from the reservoir.
The design of the radiator cap is to discourage inadvertent removal. The finger grips have been removed so 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. Also, embossed on the cap is a caution against its being opened, and arrows indicating the proper closed position.
