Radiator Cap: Description and Operation

WARNING: If there is evidence of steam, do not open hood until steam is dispersed as bodily injury could occur.

PURPOSE
A pressure vent cap issued on the cross flow radiator to allow a build up between 93 - 124 kPa (13.5 - 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 radiator cap to check engine coolant level; check coolant visually at the see through coolant reservoir. Coolant should be added only to the reservoir.

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 engine, fenders and persons nearby. If the solution contains flammable anti-freeze such as alcohol (not recommended for use at any time), there is also the possibility of causing a serious fire and severe injury.

DESCRIPTION
The pressure type radiator 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 radiator 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. 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 arrow indicating the proper closed position.