DAF CF65, CF75, CF85 Series . Manual — part 234
©
200324
3-5
Description of components
PE ENGINE COOLING SYSTEM
CF65/75/85 series
2
6
3.4 VISCOUS FAN CLUTCH
The fan is connected to the engine by means of a
viscous fan clutch. If, under certain
circumstances, the heat is not sufficiently
dissipated by the air flow passing through the
radiator, the fan will have to draw in extra cooling
air through the radiator. In a viscous fan clutch,
the drive torque is transmitted by a silicone fluid.
The fan clutch is divided into two chambers. In the
working area (1) is the rotor (2), which is
connected to the drive flange (7). The supply
chamber (3) rotates freely round the drive flange
(7) and is connected to the fan. There is silicone
fluid in the supply chamber (3). The opening (4) in
the supply chamber (3) is closed by a valve (5).
The valve (5) is operated by a bimetallic strip (6).
If the opening (4) in the supply chamber (3) is
closed by the valve (5), no silicone fluid can enter
the working area (1). The silicone fluid still
present in the working area (1) will flow back to
the supply chamber (3) through the bores (8). As
only very little fluid will be left in the working area
(1), there will be a great difference in rotating
speed (slip) between the drive flange (7) and the
supply chamber (3) with the fan.
When the air temperature increases, the
bimetallic strip (6) will bend and the valve (5) will
partially release the opening (4) in the supply
chamber (3). Through this opening, a limited
amount of silicone fluid can enter the working
area (1) and flow past the rotor (2). This will cause
friction, so that the difference in rotating speed
(slip) between the drive flange (7) and the supply
chamber (3) with the fan will decrease.
M201039
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PE ENGINE COOLING SYSTEM
3-6
©
200324
Description of components
6
CF65/75/85 series
2
As the air temperature rises, the bimetallic strip
(6) will continue to bend and the opening (4) in the
supply chamber (3) will be fully released.
The further the opening (4) in the supply chamber
(3) is released, the more silicone fluid will flow into
the working area (1) and past the rotor (2). As a
result of the increase in friction, the difference in
rotating speed (slip) between the drive flange (7)
and the supply chamber (3) will further decrease.
M201039
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©
200324
4-1
Inspection and adjustment
PE ENGINE COOLING SYSTEM
CF65/75/85 series
2
6
4. INSPECTION AND ADJUSTMENT
4.1 PRESSURE TESTING
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When the coolant is hot, there is
overpressure in the cooling system.
Carefully remove the filler cap to
release the overpressure. Coolant is
a toxic fluid. Contact with the skin
should therefore be avoided. To
avoid damaging the cylinder block;
do not top up a warm engine with
cold coolant.
If this is done when the engine is
warm, any cracks can be spotted
more quickly.
The cooling system can be checked
for leaks with a pressure-test pump.
1.
Open the grille.
2.
Remove the filler cap.
3.
Fill the cooling system to the correct level.
4.
Raise the engine temperature. This need not
be the operating temperature.
5.
Fit a pressure-test pump. Pressure-test the
system at the specified pressure. See
"Technical data".
6.
Check for leakage.
M201192
PE ENGINE COOLING SYSTEM
4-2
©
200324
Inspection and adjustment
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CF65/75/85 series
2
4.2 INSPECTION, THERMOSTAT
1.
Remove the thermostat. See "Removal and
installation".
2.
Inspect the sealing surfaces (A) of the
thermostat housing for damage.
3.
Inspect the oil seal (B) for damage.
4.
Inspect the thermostat seat (C) for damage.
5.
Check whether the thermostat is fully closed.
6.
Place the thermostat in a container filled with
clean water.
7.
Place a thermometer in the container and
heat the water. Check at which temperature
the thermostat opens and whether it opens
fully. See "Technical data".
M200742
A
B
C
M200513
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