Radiator Cap: Description and Operation

WARNING: With a pressurized cooling system, coolant temperature in the radiator can be considerably higher than the boiling point of the solution at atmospheric pressure. Removal of the radiator cap, while the cooling system is hot and under high pressure, will cause the solution to boil instantaneously with explosive force, spewing the solution over the engine, fenders and persons nearby. If the solution contains flammable antifreeze, such as alcohol (not recommended for use at any time), there is also the possibility of causing a serious fire.





DESCRIPTION
A pressure vent cap is used on the radiator. The cap contains both a pressure and a vacuum relief valve. The pressure valve is held against its seat by a spring of predetermined strength, protecting the cooling system by relieving internal pressure which exceeds design specifications. System pressure is relieved when it rises 90 kPa (12.8 psi) above normal atmospheric pressure 101 kPa (14.7 psi) at sea level. 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 off and could cause the radiator to collapse. DO NOT remove the radiator cap to check the Engine Coolant Level (ECL); check visually at the see-through coolant recovery reservoir. Coolant should be added only to the reservoir.