Cooling System: Description and Operation
Engine Cooling
COMPONENT LOCATION - NATURALLY ASPIRATED VEHICLES
COMPONENT LOCATION - SUPERCHARGER VEHICLES
INTRODUCTION
The engine cooling system maintains the engine within an optimum temperature range under changing ambient and engine operating conditions. The system is a pressurized expansion tank system with continuous bleeds to separate air from the coolant and prevent the formation of air locks. The engine cooling system also provides:
- Heating for:
- The passenger compartment. For additional information, refer to 412-02 Heating and Ventilation.
- The throttle body.
- Cooling for:
- The engine oil cooler. For additional information, refer to 303-01A Engine - 5.0L, Vehicles With: Supercharger or 303-01B Engine - 5.0L, Vehicles Without: Supercharger.
- The transmission fluid cooler. For additional information, refer to 307-02 Transmission Cooling.
The primary components of the engine cooling system are the:
- Coolant pump.
- Thermostat.
- Radiator.
- Auxiliary radiator (SC (supercharger) vehicles only).
- Cooling fan.
- Expansion tank.
- Engine oil cooler.
- Outlet tube and heater manifold.
- Connecting hoses and pipes.
COOLANT PUMP
The body of the coolant pump contains an impeller attached to a shaft supported in a bearing assembly. The impeller is driven by a pulley, pressed on to the front of the shaft, which is driven by the accessory drive belt. For additional information, refer to 303-05 Accessory Drive.
Two coolant outlet flanges attach the coolant pump to the front of the cylinder heads. A pipe connects a further coolant outlet to a pipe from the engine oil cooler. A bleed connector is installed in the front of the coolant pump, adjacent to the coolant inlet connection from the thermostat. A check valve is incorporated into the bleed connection.
THERMOSTAT
The thermostat is a multi-stage device located in the coolant pump inlet to provide fast response and control of the engine outlet temperature.
The thermostat allows rapid engine warm-up by preventing coolant flow through the radiator and by limiting coolant flow through the cylinder block when the engine is cold. During warm-up and at engines speeds above approximately 1800 rev/min, a by-pass valve opens to control the coolant flow and pressure, to protect the engine components. When the thermostat opening reaches 6 mm (0.24 in.), the by-pass flow is shut-off. When the thermostat opening exceeds 6 mm (0.24 in.), the radiator coolant flow is further controlled up to the point where the thermostat is fully open. At this point maximum radiator coolant flow is achieved to provide maximum cooling.
On both naturally aspirated and supercharger vehicles, the thermostat begins to open at 88 - 90 °C (190 - 194 °F) and is fully open at 102 °C (216 °F).
RADIATOR
Radiator (Naturally Aspirated Vehicles)
Radiator (Supercharger Vehicles)
The radiator is a cross flow type with an aluminum core and plastic end tanks. The radiator is part of the cooling module and is attached to the vehicle by locating spigots and supports integrated into the end tanks. The supports are installed in rubber bushes located in mounting brackets on the front subframe. The locating spigots are installed in rubber bushes located in mounting brackets on the front crossmember.
The two end tanks incorporate connections for the upper and lower hoses, the coolant supply hose of the transmission fluid cooler and, on SC (supercharger) vehicles, the supply and return hoses of the auxiliary radiator. A drain plug is installed in the bottom of the LH (left-hand) end tank.
AUXILIARY RADIATOR (SUPERCHARGER VEHICLES ONLY)
The auxiliary radiator is connected in parallel with the (main) radiator to increase the engine cooling capacity on SC (supercharger) vehicles. The auxiliary radiator is mounted horizontally in an air deflector attached to the front of the charge air radiator. The two end tanks of the auxiliary radiator incorporate connections for the supply and return hoses that connect it to the main radiator.
COOLING FAN
Cooling Fan (Naturally Aspirated Vehicles)
Cooling Fan (Supercharger Vehicles)
An electric, variable speed cooling fan is installed in a shroud attached to the rear of the radiator. The cooling fan is operated by a fan control module, integrated into the electric motor, under the control of the ECM (engine control module). An electrical connector at the RH (right-hand) side of the shroud provides the interface between the cooling fan harness and the vehicle wiring.
EXPANSION TANK
The expansion tank is installed on the RH (right-hand) side of the engine compartment, immediately behind the suspension turret. A filler cap, bleed screw and level sensor are incorporated into the expansion tank. MAX and MIN level markings are molded onto the exterior of the tank.
The expansion tank provides the following functions:
- Service fill.
- Coolant expansion during warm-up.
- Air separation during operation.
- System pressurization by the filler cap.
The expansion tank has an air space of approximately 0.5 liter (1.06 US pints), above the MAX level, to allow for coolant expansion.
OUTLET TUBE AND HEATER MANIFOLD
Outlet Tube
Heater Manifold
ENGINE COOLANT
The engine coolant is formulated to last for ten years or 240,000 km (150,000 miles). The coolant is silicate free and must not be mixed with conventional engine coolant.
CONTROL DIAGRAM
NOTE:
A = Hardwired
PRINCIPLES OF OPERATION
Engine Cooling Flow Diagram - Naturally Aspirated Vehicles
Engine Cooling Flow Diagram - Supercharger Vehicles
When the engine is running, the coolant is circulated around the engine cooling system by the coolant pump. From the coolant pump, coolant flows through the cylinder heads and the engine oil cooler into the cylinder block and the heater manifold.
In the cylinder block, the coolant flows forwards to the outlet tube. When the coolant is cold, the thermostat is closed and the coolant flows direct from the outlet tube back to the coolant pump. Once the coolant reaches operating temperature the thermostat begins to open, to control system temperature, and coolant flows from the outlet tube to the coolant pump via the radiator and, on SC (supercharger) vehicles, the auxiliary radiator. When the thermostat is open, the coolant flow through the radiator(s) also generates a coolant flow through the transmission fluid cooler.
From the heater manifold the coolant flows through the electronic throttle and the heater core, in parallel circuits that are unaffected by the position of the thermostat. From the electronic throttle, the coolant merges with bleed coolant from the coolant pump and the outlet tube and flows to the expansion tank. From the heater core, the coolant flows back to the inlet of the coolant pump.
Expansion and contraction of the coolant is accommodated by an air space in the expansion tank and the compliance of the flexible hoses.
If the coolant level in the expansion tank decreases below a predetermined value, the level sensor connects a ground to the instrument cluster, which activates the appropriate warning. For additional information, refer to 413-01 Instrument Cluster.
The cooling fan is operated by a fan control module integrated into the cooling fan motor. The fan control module regulates the voltage, and thus speed, of the cooling fan motor in response to a PWM (pulse width modulation) signal from the ECM (engine control module). The ECM (engine control module) calculates the required fan speed from the engine temperature, A/C (air conditioning) system pressure and transmission fluid temperature. Under hot operating conditions, the fan may continue to operate for 4 minutes after the engine has been switched off.