Cooling System: Description and Operation

DESCRIPTION
The cooling system maintains engine temperature at an efficient level during all engine operating conditions. The surge tank pressure cap must be removed in order to add coolant to the system.

OPERATION
Since the thermostat remains closed until the engine reaches the proper operating temperature, when the engine is cold coolant does not circulate through the radiator to allow for faster engine warm up. When the engine reaches normal operating temperature, the thermostat opens, and coolant begins circulating through the radiator to keep the engine from overheating. The circulation is controlled by a thermostat.

SYSTEM CIRCULATION
The engine mounted water pump is belt driven. Coolant from the radiator outlet flows to the water pump inlet and is pumped through coolant passages in the crankcase and into the cavities surrounding the cylinders. Coolant then flows through holes in the cylinder head gaskets into the cylinder head coolant passages. Passages in the intake manifold direct the coolant to the thermostat. When the thermostat is closed (cold engine), the coolant is prevented from returning to the radiator and is recirculated for quick engine warm up.

Once the engine has warmed sufficiently, the thermostat opens and coolant flows to the inlet tank on the top left side of the radiator. It is cooled as it flows across the horizontal core tubes to the outlet tank on the right side of the radiator, completing the cycle. The cooling system draws coolant from the radiator by the coolant pump and passes it through the thermostat on the inlet side of the pump. The coolant enters the block at the rear of the engine from the water crossover and then it is routed through the cylinder heads back to the water crossover. At this point, the coolant has four possible routes; the radiator, the bypass, the heater core, and the throttle body heater circuit. The cooling system is sealed by a pressure type radiator filler cap which causes the system to operate at pressures higher than atmospheric pressure. This higher pressure raises the boiling point of the coolant and increases the cooling efficiency of the radiator.

COOLING FANS
The cooling system utilizes two plastic fans. The fans are driven by individual electric motors which are controlled electronically by the Powertrain Control Module (PCM). Fan speed is variable and is controlled based on engine coolant and A/C high pressure refrigerant temperature. Both fans are commanded "ON" at low speed at a calibrated engine coolant or A/C high pressure refrigerant temperature increases and reaches full power at a higher calibrated engine coolant or A/C high pressure refrigerant temperature. Undesirable on off operation of the fans is eliminated by utilizing turn off temperatures lower than the turn on temperatures. When the system demands more cooling, the left fan will operate at high speed until the demand has been met. Cooling fan(s) are operated by a relay(s) and switches.

WARNING: An electric fan under the hood can start up even when the engine is not running and can injure you. Keep hands, clothing and tools away from any underhood electrical fan.