Pressure Cap
WARNING: This page does not describe the selected car, but rather 21 other vehicles, including the 1983 Plymouth Turismo, 1983 Plymouth Scamp Pickup, 1983 Plymouth Sapporo, 1983 Plymouth Reliant, and 1983 Plymouth Horizon. However, it is still accessible from the selected car via links, so may be relevant.
All models use a 16 psi (1.1 kg/cm2 ) pressure cap which should be tested at 14-17 psi (1.0-1.2 kg/cm2 ). Center of cap is equipped with a vent valve. Vent valve allows a small flow through the cap when temperature is below boiling point. Valve closes when boiling point is reached. Valve also opens when coolant is cooling and contracting, permitting liquid to return to radiator from coolant reserve tank.