Cooling System: Description and Operation
DESCRIPTIONThis vehicle has a pressure-type engine cooling system. A thermostat controls the temperature of the coolant that circulates through the engine coolant passages, the radiator and the heater core. This circulation is forced by an impeller-type pump. The system is sealed by a pressure-regulated radiator cap. This cap contains a common pressure/vacuum valve. The pressure valve actuates at approximately 15 psi (103 kPa). As the engine coolant temperature rises, the coolant volume expands and system pressure rises. This increased pressure raises the temperature at which the coolant will boil. This permits the engine to operate more efficiently.
PRESSURE LIMIT
When an internal cooling system pressure of 15 psi (103 kPa) is reached, the pressure valve in the radiator cap opens and air, coolant vapor and coolant pass to the reservoir. Air and vapor escape from the reservoir through a vent. Coolant remains in the reservoir until a decrease in cooling system temperature causes the pressure to fall. When the cooling system drops below atmospheric pressure, the radiator vacuum valve opens and coolant is drawn back into the radiator, equalizing the pressure in the cooling system with atmospheric pressure.