Cooling System: Description and Operation

This 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.

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 tall. 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.

The radiator cooling fan is mounted immediately behind the radiator within a circular shroud. It has eight blades and is approximately 16 inches in diameter. This fan is belt-driven. The clutch is activated and de-activated both thermally and by engine speed. The clutch engages when the radiator temperature exceeds a high temperature threshold. Likewise, the clutch disengages when it falls below the low temperature threshold. Also, the clutch disengages when the engine speed exceeds the high speed threshold. When engine speed falls below the low speed threshold, the clutch engages to provide cooling when there is low air flow resulting from low speed.