LR3/Disco 3
GENERAL
The cooling system employed is of the pressure relief by-pass type, which allows coolant to circulate around the engine
and the heater circuit while the thermostat main valve 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 transmission fluid and engine oil.
The cooling system comprises:
A radiator
A passenger compartment heater matrix
An Engine Oil Cooler (EOC)
A coolant pump
A Pressure Relief Thermostat (PRT)
An expansion tank
A viscous fan
Connecting hoses and pipes.
ENGINE COOLING SYSTEM
The coolant is circulated by a centrifugal pump mounted on the front of the engine and driven by an ancillary drive
'polyvee' belt. The coolant pump circulates coolant through the cylinder block and cylinder heads via a chamber located in
the 'vee' of the engine. Having passed through the engine the coolant returns to the thermostat housing via the bypass
pipe. Coolant also circulates through the top hose to the heater matrix. The coolant returns via the EOC to the engine side
of the PRT.
The PRT housing contains a normal thermostat, which is positioned such that the wax's temperature is controlled by both
the coolant from the radiator and the bypass. This results in the thermostat being able to vary its opening temperature
dependant on ambient conditions. The PRT also contains a sprung loaded valve, which limits the amount flow using the
bypass. This means that the engine can run without coolant flowing through the bypass temporarily, to improve heater
performance.
The radiator is a cross flow type with an aluminium matrix and has a drain tap on the lower right-hand rear face. The lower
radiator mountings are located part way up the end tanks. The mountings are fitted with rubber bushes, which sit on the
upper chassis rails. The radiator upper is mounted by pins, which are pushed through rubber bushes mounted in the
Front End Carrier (FEC) above the radiator. The radiator also incorporates two connections for the transmission oil cooler
pipes.
The radiator top hose is connected to the PRT by the bypass hose and the bottom hose is directly connected to the outlet
side of the thermostat housing.
The expansion tank is fitted forward of the LH suspension turret in the engine compartment. The expansion tank allows
for the expansion of the coolant as the engine gets hot and also supplies the engine with coolant as the coolant in the
engine contracts. The tank also allows any air trapped in the coolant to be removed.
The liquid cooled transmission fluid cooler is mounted in the cold side radiator end tank. It is positioned in the middle of
the LH end tank.
For additional airflow through the radiator matrix, particularly when the vehicle is stationary, there is an engine driven
Viscous fan unit fitted to the rear of the radiator. The fan is used for engine cooling and for Air Conditioning (A/C) system
12
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Radiator bottom hose
13
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Engine oil cooler (if fitted)
14
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Hose (for vehicles without engine oil cooler)
15
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Hose, inlet and outlet (for vehicles with engine oil cooler)
16
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Cooling fan
17
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Transmission oil cooler pipes
18
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Radiator cowl, lower
19
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Radiator
20
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Radiator cowl, upper
