Cooling System: Description and Operation

The Saturn cooling system has two unique features, a coolant recovery reservoir and an inlet side thermostat. The system is filled through the pressure cap and doesn't require any bleeding. Flow from the tank fills the engine cylinder block, radiator, heater core, and hoses.
During engine operation with the thermostat closed, coolant is pumped through the cylinder block, cylinder head, heater core inlet hose, heater core, heater outlet hose and back to the thermostat housing. Coolant flows past the thermostat element and back to the water pump inlet. Some coolant is routed back through the engine block to the thermostat cavity. A thermostat by-pass valve controls return coolant flow through the cylinder block and dampens sudden coolant pressure surges by venting coolant back to the water pump suction side.
When the thermostat begins to open the by-pass valve begins to close the cylinder block passage. Coolant flow is then routed from the pump through the cylinder block, head, heater inlet, heater core, heater outlet and back to the cylinder block. Coolant is also routed through the upper radiator hose, radiator core, lower or outlet radiator hose past the thermostat to the water pump. Coolant flow from the heater return and lower radiator hose wash the thermostat element, thus regulating coolant flow through the lower radiator hose and to the water pump.

IMPORTANT: During extremely cold weather, 10° F (-12° C) or colder, the engine's coolant temperature will decrease quickly when idling with the the heater fan on high speed, and cool air may flow from the heater outlets. The fan control switch should be set at a slower speed position (fan speed I or II) to maintain the hottest air flow.

The Saturn cooling system is filled with Dex-Cool(TM), a non phosphate, silicate free ethylene glycol-based antifreeze recommended for aluminum engine protection and increased water pump seal life.