Description

Description

General
The engine cooling system maintains the engine within the optimum operating temperature range under varying ambient temperature and engine load conditions. In addition, the system cools the engine oil, the Intermediate Reduction Drive (IRD) and the transmission fluid, and provides the heat source for passenger compartment heating. The system consists of
^ A coolant pump.
^ A radiator.
^ A Pressure Relief Thermostat (PRT).
^ An expansion tank.
^ Interconnecting hoses and coolant rail.
^ Two cooling fans
^ Heater diverter valve (NAS and Gulf States only - From 2003 Model Year)
Engine oil and transmission fluid are cooled by plate type heat exchangers. The engine oil cooler is attached to the sump at the front of the engine. The transmission oil cooler is attached to the front of the gearbox. The IRD is cooled by an internal plate type heat exchanger incorporated into the IRD lubrication circuit.

Coolant Pump
The rotor type coolant pump Is Integrated into the front of the engine, between the cylinder blocks. The pump is driven by the camshaft timing belt via a plain pulley installed on the pump rotor shaft. The pulley also acts as an Idler pulley for the camshaft timing belt.

Radiator
The radiator is a cross flow type with an aluminum matrix and molded plastic end tanks. The bottom of the radiator is located in rubber bushes on the front lower crossmember. The top of the radiator is secured to the bonnet locking platform by threaded retainers. The top hose connects the radiator to a coolant outlet elbow In the cylinder block. The bottom hose connects the radiator to the thermostat housing.

Pressure Relief Thermostat (PRT)
The PRT is installed in a housing located in a coolant outlet port in the cylinder block, between the cylinder banks. The thermostat housing incorporates inlet connections for the bottom hose and the return hose from the IRD cooler/heater/transmission cooler. A pipe connects the outlet side of the thermostat housing to the coolant pump inlet.

The thermostat is located in the inlet side of the cooling circuit, which provides a more stable control of the coolant temperature in the engine. The housing contains a wax element and a spring loaded by-pass flow valve. The PRT senses all parameters such as engine speed, engine heat input and ambient temperature and reacts according to the actual operating conditions of the engine.

The wax element thermostat is used to maintain the coolant at the optimum temperature for efficient combustion and assist engine warm-up. The thermostat is closed at low coolant temperatures with the flow being controlled by the by-pass valve. When the coolant temperature reaches approximately 88°C (190°F), the thermostat begins to open and is fully open at approximately 102°C (216°F).

Expansion Tank
The expansion tank is installed in the rear RH comer of the engine compartment. The expansion tank provides a reservoir of coolant and accommodates the increase in coolant volume produced by heat expansion. A cap on the expansion tank provides a system filling point and incorporates a pressure relief valve that releases pressure from the system if it exceeds 1 bar (14.5 lbs/in2). Expansion pipes connect the expansion tank to the radiator and the inlet manifolds. A hose connects an outlet on the expansion tank to the coolant rail.

Hoses and Coolant Rail
The coolers and the heater matrix are connected together, by hoses and the coolant rail, in a circuit from the outlets at the right front comer of the cylinder block and the top hose to the return hose connection on the thermostat housing. The hoses connected to the IRD cooler are covered by heat shielding to protect them from heat radiated by the exhaust system. A bleed screw In the heater outlet hose enables air to be bled from the system during filling.

Cooling Fans
The two cooling fans are variable speed electric fans installed in a housing attached to the rear of the radiator. The motor of each cooling fan is powered by a supply from a cooling fan ECU installed behind a cover in the top left comer of the cooling fan housing. An air scoop on the cooling fan housing directs cooling air over the ECU.

Heater Diverter Valve (NAS and Gulf States Only) - From 2003 Model Year
The heater diverter valve increases the flow of coolant through the heater matrix at low engine speeds to improve the low engine speed heater performance.

The valve comprises a spring loaded valve integrated into the 'T' connector on the thermostat by-pass hose. The construction and operating principles of the valve is similar to that of the pressure relief thermostat (PRT).