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GM/Detroit 6.5L – RADIATOR CAP

A pressure-vent cap allows a buildup of 103 kPa (15 psi) in the cooling system. This pressure raises the boiling point of the coolant to about 128°C (262°F) at sea level. Do not remove the radiator cap to check the engine coolant level; check the coolant visually at the see-through coolant reservoir. Add coolant to the reser­ voir when the system cools.

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 radiator cap while the engine is hot and the pressure is high will cause the solution to boil instan­ taneously and possibly with explosive force, spewing the solution over the engine, fend­ers, and person removing the cap. 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.

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 spring of pre-determined strength, which protects the radiator by relieving internal pressure when it exceeds cooling system design limits. 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 which otherwise might cause the radiator to collapse (figure 1).

The radiator cap is designed to discourage inadver­ tent removal. To safely remove the cap, rotate the cap slowly to the left, without pressing down, to the detent (figure 2). Allow any pressure to relieve. Next, press down on the cap and continue to rotate the cap to the left and lift off the cap.

Under the diaphragm spring at the top of the cap is a gasket. Embossed on the cap is a caution against its being opened and arrows indicating the proper closed position (figure 3).

The seal of the filler cap and the operation of the pressure relief valve can be checked using a conventional cooling system testing kit such as J 24460-01 (figure 4).

 

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