Cooling System: Description and Operation

Engine Cooling System

WARNING: Never remove the expansion tank cap under any circumstances while the engine is operating. Failure to follow these instructions could result in damage to the cooling system engine and/or personal injury. To avoid having scalding hot water or steam blow out of the cooling system, use extreme care when removing the expansion tank cap from a hot cooling system. Wait until the engine has cooled, then wrap a thick cloth around the expansion tank cap and turn it slowly until the pressure begins to release, step back while the pressure is released from the cooling system. When certain all the pressure has been release (still with a cloth) turn and remove the expansion tank cap. Failure to follow these instructions will result in personal injury.

WARNING: To avoid the possibility of person injury or damage to the vehicle, do not operate the engine with the hood open until the fan blade has been examined for possible cracks and separation. Failure to follow this instruction will result in personal injury.

WARNING: Disconnect the fan control wiring prior to performing any underhood service since the cooling fan motor could cycle if the ignition switch is left in the RUN position. Failure to follow this instruction will result in injury.

NOTE: The engine cooling system must be maintained with the correct concentration and type of anti-freeze solution to prevent corrosion damage.

The cooling system consists of:
- A radiator.
- Expansion tank cap.
- Coolant thermostat.
- Water pump.
- Engine cooling fan motors and fan blades which are activated by the Powertrain Control Module (PCM) through two ISO relays in the battery junction box located near the battery in the engine compartment.
- A separate coolant expansion tank located beside the radiator helps to maintain the correct volume of engine coolant.

The water pump is of a conventional design and is driven by the left-hand side intake camshaft through a drive belt on 2.5L vehicles and by the crankshaft pulley through the accessory drive belt on 2.0L vehicles.

The coolant thermostat:
- Is located in the coolant thermostat housing.
- Allows rapid engine warm-up by restricting engine coolant flow at lower operating temperatures.
- Assists in keeping the engine operating temperature within predetermined limits.

The engine cooling system operates as follows:
- Coolant enters the radiator through the radiator inlet tank.
- Coolant flows through the radiator tubes and is cooled by air passing over the cooling fins assisted by the fan control and the fan blades.
- Coolant is then circulated from the radiator outlet tank where it mixes with coolant from the radiator coolant expansion tank and passes through the coolant thermostat housing.
- Coolant then goes through the water pump and into the cylinder block and cylinder heads on the 2.5L vehicles and through the cylinder head and into the cylinder block on 2.0L vehicles.
- Coolant then flows out of the engine through the water crossover (2.5L engine) or through the coolant thermostat housing (2.0L engine) to complete the circuit.

Electrical System
The fan control system consists of:
- Powertrain Control Module (PCM).
- Air Conditioning (A/C) pressure cut-off switch.
- High speed cooling Fan Control (FC) relay.
- Low speed cooling fan control (FC) relay.
- Engine cooling fan resistor.
- Engine cooling fan motor.

The Powertrain Control Module (PCM) determines the cooling fan motor requirements and controls the fan operation through the low speed fan control and high speed fan control outputs. The PCM outputs complete the ground side of the relay coil circuits. Power to the relay coil circuits is provided by the PCM power relay.

If low speed fan operation is required, the PCM grounds the low speed fan control output. This energizes the low speed FC relay coil which closes the low speed FC relay contacts. Power flows through the fuse 2 (60A), the low speed FC relay contacts, the engine cooling fan resistor, and the engine cooling fan to ground. The engine cooling fan resistor provides thermal overload protection for the low speed fan control circuit.

If high speed fan operation is required the PCM grounds the high speed FC relay coil which closes the high speed FC relay contacts. Power flows through the fuse 2 (60A), the high speed FC relay contacts and the engine cooling fan to ground.

High speed fan operation may also be commanded by the dual pressure A/C pressure switch. The medium pressure contacts of the A/C pressure switch turn on the high speed cooling fan when A/C head pressure reaches a predetermined level grounding the air conditioning pressure switch. This grounds the high speed FC relay circuit. This closes the high speed FC relay contacts and turns on the high speed cooling fan.

If A/C head pressure drops below the predetermined level, the medium pressure contacts open returning the high speed FC relay operation to the PCM.

Coolant Recovery System

NOTE: When the coolant thermostat is closed, there is no flow through the radiator coolant expansion tank.

A pressurized radiator coolant expansion tank system is used which continuously separates the air from the cooling system.
- When the coolant thermostat is open, coolant flows through the hose from the bottom of the expansion tank into the radiator lower hose.
- The expansion tank separates any trapped air from the cooling system and replenishes the system through its coolant expansion tank hose attached to the water outlet hose.

The expansion tank serves as the location for:
- Service fill.
- Coolant expansion during warm-up.
- System pressurization from the expansion tank cap.
- Air separation during operation.
- The expansion tank is designed to have approximately 0.5 to 1 liter of air when cold to allow for coolant expansion.