Radiator Cap: Description and Operation

The cooling system is equipped with a pressure cap that releases built up pressure, maintaining a range of 97-124 kPa (14-18 psi).
The cooling system will operate at higher than atmospheric pressure. The higher pressure raises the coolant boiling point thus, allowing increased radiator cooling capacity.

Figure 7:

There is a vent valve in the center of the cap that allows a small coolant flow from the Coolant Reserve System (CRS) tank. This valve is spring loaded in the closed position. However it must be free to open during system cool-down. If the valve is stuck shut, the radiator hoses will collapse on cool-down. Clean the vent valve to ensure proper sealing function.
There is a gasket in the cap that seals to the top of the filler neck so that vacuum is maintained to draw coolant back into the system from the Coolant Reserve System (CRS) tank.