Radiator Filler Cap Replacement Description

A pressure-vent cap allows a buildup of 105 kPa (15 psi) in the cooling system. The pressure increases the boiling point of the coolant to 125°C (257°F) at sea level. Only remove the radiator cap from a cool engine. Do not remove the radiator cap in order to check the engine coolant level. Check the coolant level visually, at the plastic see-through coolant reservoir. Add the coolant to the reservoir when the system cools. Under some conditions, the ethylene glycol in the engine coolant is combustible. To help avoid being burned, Do not spill the coolant on the exhaust system or on hot engine parts.

Radiator Filler Cap Replacement Operation

Caution: Under pressure, the temperature of the solution in the radiator can be considerably higher, without boiling. Removing the radiator cap while the engine is hot (pressure is high), will cause the solution to boil instantaneously, with explosive force. The solution will spew out over the engine, fenders, and the person removing the cap. Serious bodily injury may result. Flammable antifreeze, such as alcohol, is not recommended for use at any time. Flammable antifreeze could cause a serious fire.

The pressure-type radiator filler cap contains a blow-off valve and a vacuum valve. The pressure blow-off valve is held against its seat by a spring of predetermined strength. Internal pressure is relieved as it exceeds cooling system design limits, protecting the radiator.The vacuum valve is held against its seat by a light spring. This permits the valve to open, and relieve the vacuum created as the system cools off. The vacuum might otherwise collapse the radiator. The design of the radiator cap discourages inadvertent removal. To safely remove the cap, rotate the cap slowly counterclockwise (do not press down) to the detent. Allow any pressure to vent. Next, press down on the cap and continue to rotate the cap counterclockwise, then lift the cap off. Under the diaphragm spring at the top of the cap is a rubber gasket. Embossed on the cap is a caution against its being opened and arrows indicating the proper closed position. For radiator cap testing, refer to Radiator Leak Testing (On and Off Vehicle) .