Pressure Cap
WARNING: This page does not describe the selected car, but rather 16 other vehicles, including the 1984 Plymouth Turismo, 1984 Plymouth Reliant, 1984 Plymouth Horizon, 1984 Plymouth Gran Fury, and 1984 Dodge Rampage. 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.