Cooling System: Description and Operation

3.0L Engine

4.0L Engine

WARNING: NEVER REMOVE THE COOLANT EXPANSION TANK CAP UNDER ANY CIRCUMSTANCES WHILE THE ENGINE IS OPERATING. FAILURE TO FOLLOW THESE INSTRUCTIONS MAY RESULT IN DAMAGE TO THE COOLING SYSTEM OR 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 COOLANT EXPANSION TANK CAP FROM A HOT COOLING SYSTEM. WAIT UNTIL THE ENGINE HAS COOLED, THEN WRAP A THICK CLOTH AROUND THE COOLANT EXPANSION TANK CAP AND TURN IT SLOWLY UNTIL THE PRESSURE BEGINS TO RELEASE, STEP BACK WHILE THE PRESSURE IS RELEASED FROM THE SYSTEM. WHEN CERTAIN ALL THE PRESSURE HAS BEEN RELEASED (STILL WITH A CLOTH) TURN AND REMOVE THE COOLANT EXPANSION TANK CAP. FAILURE TO FOLLOW THESE INSTRUCTIONS MAY RESULT IN PERSONAL INJURY.

WARNING: TO AVOID THE POSSIBILITY OF PERSONAL 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 MAY 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 ENGINE HAS BEEN SWITCHED OFF. FAILURE TO FOLLOW THIS INSTRUCTION MAY RESULT IN PERSONAL 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 the following:
Radiator
Coolant expansion tank cap
Thermostat
Water pump
Electric fan
Coolant expansion tank

The water pump is of a conventional design and is driven by the crankshaft pulley through the accessory drive belt.

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.

3.0L Engine

The engine cooling system operates as follows:
Coolant flows from the radiator and partially splits the coolant flow between the thermostat and the engine oil cooler
Coolant then flows through the water pump and partially splits the coolant flow between the right-hand and left-hand cylinders
Coolant then flows from the engine block and partially splits the coolant flow between the heater and the return hose to the radiator
Coolant returns from the heater through an additional water pump which is fitted to 4.0L engines only

Coolant Recovery System
A pressurized radiator coolant expansion tank system is used which continuously separates the air from the cooling system.
The coolant expansion tank separates any trapped air from the cooling system and replenishes the system through its coolant expansion tank feed hose attached to the heater return 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.

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 Oil Cooler
The engine oil cooler for both 3.0L and 4.0L engines are a Modine oil to water type. The oil cooler on the 3.0L engine is located on the left-hand side of the engine and is fitted to the oil filter housing. The oil cooler on the 4.0L engine is located at the front of the engine and is fitted between the oil filter housing and the oil filter.

The coolant supply and return for the oil cooler is from the radiator bottom hose.

An orifice in the bottom hose creates flow through the oil cooler.

Cooling Fan
A single, variable speed cooling fan motor is attached to a fan shroud located behind the radiator. The speed is determined by the Cylinder Head Temperature (CHT) on the 3.0L engine or the Engine Coolant Temperature (ECT), on the 4.0L engine. The air conditioning pressure and transmission oil temperature contributes to the cooling fan speed on both 3.0L and 4.0L engines.

Under hot operating conditions, the fan may continue to operate for four minutes after the engine has been switched off. An electric water pump runs for between one and ten minutes on the 4.0L engine only.

Engine Coolant
The long life engine coolant is formulated to last for five years or 150,000 miles (240,000 km). The coolant is silicate free and orange in color. The long life engine coolant must not be mixed with conventional engine coolant.