Pressure Cap Description

Caution: With a pressurized cooling system, the coolant temperature in the radiator can be considerably higher than the boiling point of the solution at atmospheric pressure. Removal of the surge tank cap, while the cooling system is hot and under high pressure, causes the solution to boil instantaneously with explosive force. This will cause the solution to spew out over the engine, the fenders, and the person removing the cap. Serious bodily injury may result.

The cross flow radiator uses a pressure vent fill cap to allow buildup of 83 kPa (12 psi) in the cooling system. The radiator cap allows the system to operate at a higher than atmospheric pressure. This pressure raises the boiling point of the engine coolant to about 12°'C (262°F) at sea level, which increases the cooling efficiency of the radiator.
The pressure-type cap contains a blowoff (pressure) valve (2) and a vacuum (atmospheric) valve (1).
A spring of a predetermined strength holds the pressure valve against the valve's seat. This spring protects the radiator by relieving any pressure that exceeds design limits.
Do the following In order to safely remove the radiator cap from a cool system:

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

1. Slowly rotate the radiator cap counterclockwise 114 turn and then stop, do not press down.
2. Allow any residual pressure, indicated by a hissing sound, to be relieved.
3. After the hissing stops, continue to rotate the radiator cap counterclockwise until the radiator cap is removed.
4. Retighten the cap, by rotating the radiator cap clockwise using hand tight pressure.