Coolant Bottle Pressure Cap
The coolant bottle is equipped with a pressure cap which releases pressure at some point within a range of 16-18 psi (110-124 kPa). See Fig 1 . The system will operate at higher than atmospheric pressure which raises coolant boiling point thus allowing increased radiator cooling capacity.
There is a spring-loaded vent valve in center of cap that allows system to pressurize and depressurize without creating a vacuum. If valve is stuck open, coolant will escape to overflow hose. There is also a gasket in cap to seal to top of filler neck.
CAUTION:
Use only pressure cap specified for this vehicle. Use of other pressure caps can lead to coolant loss and overheating.