Cooling System: Description and Operation

Engine Cooling System 2.0L (1 Of 2):

Engine Cooling System 2.5L (1 Of 2):

The cooling system consists of the following:
^ Radiator
^ Coolant expansion tank cap
^ 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 Hi 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 thermostat:
^ Is located in the 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 fail 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.

Refer to Specifications for the cooling system capacity.

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 coolant expansion tank into the radiator lower hose.

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

Radiator - Aluminum Core, Crossflow
The radiator is of the tube and louvered fin core-type with the tubes arranged horizontally for crossflow of the coolant.
^ Two Tanks, one at each side of the radiator, provides uniform distribution of the coolant to the crossflow tubes.
^ The radiator tank on the right-hand side of the radiator contains a transaxle of cooler for the automatic transaxle fluid (if equipped).

Cooling Fan, Electric

WARNING: The engine electric cooling fan motor may come on at any time without warning, even if the engine is not running. Failure to follow these instructions may result in personal injury.

The fan control system consists of:
^ Fan blades.
^ Two, two-speed cooling fan motors attached to a fan shroud located behind the radiator.
^ The cooling fan motors are wired to operate only when the ignition switch is in the RUN position, thereby preventing cooling fan motor operation after the ignition switch is turned to the OFF position.

Coolant Thermostat
When the coolant is cold, the coolant thermostat is in the closed position and the coolant flow is restricted to the cylinder block, cylinder head(s) and heater system.

As the engine coolant temperature increases, the coolant thermostat opens and allows the coolant to pass into the radiator.

Engine Coolant
The Organic Acid Technology (OAT) engine coolant is formulated to last for 6 years or 240,000km (150,000 inches). The coolant is silicate free and orange in color. OAT engine coolant should not be mixed with conventional engine coolant.