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

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. Inspect 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 Dex--Cool® 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.

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 pressure 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 Cooling System Leak Testing .