B350 1 Ton Van V6-239 3.9L (1990)
Fan Clutch: Description and Operation
Thermal Control Fan Drive
Thermal Control Fan Drive
The thermal control fan drive consists of the viscous fan drive clutch and a thermostatic spring coil mounted on it's front face. The viscous fan drive
clutch is essentially a silicone-fluid-filled coupling connecting the fan assembly to the fan/water pump pulley. The coupling allows the fan to be driven in
a normal manner at low engine speeds while limiting the top speed of the fan to a predetermined maximum level at higher engine speeds.
The thermostatic spring coil reacts to the temperature of the radiator discharge air and engages the drive clutch for higher fan speed if the air temperature
from the radiator rises above a certain point. Until additional engine cooling is necessary, the fan will remain at a reduced RPM regardless of engine
speed. Only when sufficient heat is present in the air flowing through the radiator core to cause a reaction from the thermostatic spring coil will the
viscous drive clutch engage and increase fan speed to provide the necessary additional engine cooling.
Regardless of increased engine speed, once the fan has reached its maximum operating speed it will not rotate any faster. When the necessary engine
cooling has been accomplished causing a reduction in the temperature of the radiator discharge air, the spring coil again reacts and the fan speed is
reduced to the previous disengaged speed.
