Range Rover P38
26
COOLING SYSTEM
NEW RANGE ROVER
10
DESCRIPTION AND OPERATION
Engine hot - from 99MY
When normal engine running temperature is reached,
the main valve of the thermostat opens and a
secondary valve closes the bypass port from the top
hose. With the thermostat open, coolant is circulated
through the top hose to the radiator.
The air flowing between the tubes cools the coolant as
it passes through the radiator. A controlled flow of the
lower temperature coolant is drawn from the base of
the radiator, through the bottom hose, by the water
pump and blended with hot coolant returning from the
heater matrix. Coolant circulation through the cylinder
block and cylinder heads to the heater matrix and
throttle housing remains the same.
A bleed pipe connects the top of the radiator to the
expansion tank and aids bleeding of air from the
coolant system. The expansion tank cap contains a
pressure valve which allows excessive pressure and
coolant to vent to the overflow pipe if the system has
been overfilled.
Viscous fan
There are two main components of the viscous fan
drive : An input (drive) member consisting of a
threaded shaft passing through a bearing into the
clutch plate and secured to the water pump. An output
(driven) member comprises the main body to which
the fan attaches, with the temperature sensing
mechanism (bi-metal coil) and pump plates.
The fan drive only has to be engaged periodically,
between 5% and 10% of the time during normal
driving conditions, because usually the vehicle is
cooled by ram air.
A bi-metal coil senses air temperature behind the
radiator. When a pre-determined temperature is
reached, the coil opens a valve which allows fluid to
enter the drive area. Centrifugal force circulates the
fluid to the annular drive area. There are two sets of
annular grooves, 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 then re-circulated to the reservoir via
the pump plate adjacent to the drive member.
If the engine speed is increased, the amount of slip
will also increase to limit the maximum fan speed.
Viscous unit disengaged (engine at normal
operating temperature)
1. Input (drive) member
2. Output (driven) member
3. Running clearance
4. Pump plate
5. Valve (closed)
6. Sensing mechanism (bi-metal coil)
7. Fluid seal
8. Bearing,input member
9. Fluid chamber
10. Fluid reservoir