Cooling System: Description and Operation

Engine Cooling





Description
The V8i engine uses a pressurized cooling system and cross flow radiator which is supplied from a separate expansion tank. The coolant radiator also incorporates a section at the side for cooling the engine oil. The transmission fluid cooler is mounted below the radiator.

The belt driven viscous fan and centrifugal water pump is located in the engine front cover with ports for circulation of coolant to both banks of cylinders and cylinder heads. Coolant returns to the top of the radiator via ports in the inlet manifold where the thermostat is mounted horizontally.

Coolant also circulates through the vehicle heating system and is used to heat air entering the inlet manifold plenum chamber.

Operation

Cooling System:

Coolant Circulation
When the engine is started from cold the thermostat prevents any coolant circulation through the radiator by closing off the top hose. During the engine warm up period, the water pump, pumps coolant around the cylinders to the rear of the cylinder block along the main galleries in both cylinder banks. At the rear of the cylinder block the coolant rises through a large port in each cylinder head/block joint face, and then flows forward to connect with ports at the front of the inlet manifold. From the manifold the coolant is carried by an external pipe to the heater unit and from the heater through another external pipe to the pump inlet.

The coolant circulation through the cylinder block and heads, does not change when normal running temperature is reached and the thermostat opens. But, with the thermostat open, coolant also flows through the top hose to the radiator where it is cooled and drawn back into the pump via the bottom hose.

Throttle Housing Heating
The base of the throttle housing is heated by a flow of coolant from the inlet manifold which returns through a long hose, to the top right corner of the radiator. The throttle housing is heated to prevent throttle disc icing.





Viscous Fan
The viscous drive unit for the engine cooling fan, provides a means of controlling the speed of the fan relative to the running temperature of the engine. The viscous unit is a type of fluid coupling, which drives the fan blades by means of silicone fluid.

The fan drive has to be engaged only periodically, between 5% and 10%, during normal operating conditions, because the engine is cooled by ram air for most of the time.








To engage and disengage the fan drive, the bi-metal coil senses air temperature behind the radiator. When a pre-determined temperature is reached, the coil opens a valve (5 in the illustration) which allows fluid to enter the drive area and, due to centrifugal force, circulates to the annular drive area.

There are two sets of annular grooves (3), one in the drive clutch and the other in the drive body, a specific clearance being provided between the two sets of grooves.

When this clearance is filled with viscous fluid, a shearing action, caused by the speed differential between the two drive components, transmits torque to the fan. The fluid is thrown to the outside of the unit by centrifugal force from where it is recirculated to the reservoir (10) via the pump plate (4) adjacent to the drive member.

If the engine speed is increased, the amount of slip will also increase to limit the maximum fan speed.

When the air temperature from the radiator drops sufficiently, the bi-metal coil closes the valve and prevents fluid from entering the drive area. The fluid that is in the drive area will gradually pump out into the reservoir (10) and the fan will return to an idle condition.
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