Cooling system - Td4 (Description): Description and operation

Description

General

The cooling system employed is the bypass type, which allows coolant to circulate around the engine and the heater circuit while the thermostat is closed. The primary function of the cooling system is to maintain the engine within an optimum temperature range under changing ambient and engine operating conditions. Secondary functions are to provide heating for the passenger compartment and cooling for the Intermediate Reduction Drive (IRD), engine oil and, on automatic gearbox models, the Exhaust Gas Recirculation (EGR) system and transmission fluid.

The cooling system comprises: l A radiator l A passenger compartment heater matrix l An IRD cooler l An EGR cooler (automatic gearbox models only) l A transmission fluid cooler (some automatic gearbox models) l Engine oil cooler l A coolant pump l A thermostat l An expansion tank l Two cooling fans l Connecting hoses and pipes l A fuel burning heater (selected markets only).

The coolant is circulated by a centrifugal type pump mounted on the front of the engine and driven by the ancillary drive 'polyvee' belt. The coolant pump circulates coolant around the cylinder block and cylinder head, to the radiator, engine oil cooler, IRD cooler, heater matrix and, where fitted, the EGR and transmission fluid coolers, via the coolant hoses. A bleed screw is installed in the return hose from the heater matrix to bleed air from the cooling system during filling.

The thermostat is located in a housing attached to the coolant pump on the inlet side of the cooling circuit. This provides a more stable control of the coolant temperature in the engine.

The radiator is a cross flow type with an aluminium matrix and moulded plastic end tanks. The radiator end tanks have brackets which allow for the attachment of the fan assembly, intercooler and, if fitted, air conditioning system condenser. The bottom of the radiator is located in rubber bushes supported by plastic brackets which are clipped into the body longitudinals. The top of the radiator is located in rubber bushes secured by brackets fitted to the bonnet locking platform.

The radiator top hose is connected to a coolant outlet elbow which is bolted to the cylinder head. The elbow also has a connection for the feed to the heater matrix via the coolant rail on the side of the engine. The radiator bottom hose is connected to a pipe which is routed around the front of the engine and connected to the coolant pump housing.

An expansion tank is fitted to the RH suspension turret in the engine compartment. The expansion tank allows for expansion of the coolant when the engine is hot and replaces the coolant into the system as the engine cools down.

The IRD oil is cooled with fluid from the cylinder block. The fluid passes through a plate type heat exchanger located in the IRD. The plate contains waterways which cool the IRD oil and recirculates the coolant via the heater circuit.

The EGR cooler, fitted to automatic gearbox models, is located in the coolant return line from the engine oil cooler to the coolant pump. The fluid cools the exhaust gases returning to the inlet manifold, which improves emissions. The cooler incorporates a bleed screw to bleed air from the cooler when filling the cooling system.

On automatic gearbox models fitted with a liquid cooled transmission fluid cooler, the cooler is located at the front of the gearbox. The cooler receives coolant from the radiator bottom hose, which passes through the cooler and is returned into the bottom hose.

Where fitted, the Fuel Burning Heater (FBH) is located behind the front of the LH wheelarch liner. The unit is connected in series with the coolant supply to the heater matrix. For further details refer to Heating and Ventilation. HEATING AND VENTILATION, DESCRIPTION AND OPERATION, Description.