VISCOUS FAN DRIVE
| CAUTION | If viscous fan drive is replaced because of mechanical damage, cooling fan blades should also be inspected. Inspect for fatigue cracks, loose blades or loose rivets that could have resulted from excessive vibration. Replace fan blade assembly if any of these conditions are found. Also inspect water pump bearing and shaft assembly for any related damage due to a viscous drive malfunction. |
The thermal viscous fan drive consists of the viscous fan drive clutch and a thermostatic spring coil mounted on its front face. The viscous fan drive clutch is s silicone-fluid-filled coupling connecting fan blade assembly to water pump shaft. The coupling allows fan to be driven in a normal manner at low engine speeds. It will limit top speed of fan to a predetermined maximum level at higher engine speeds. The thermostatic spring coil reacts to the temperature of radiator discharge air. It engages drive clutch for higher fan speed if air temperature from radiator rises above a certain point. Until additional engine cooling is necessary, fan will remain at a reduced RPM regardless of engine speed. Only when a sufficient heat is present in the air, will the viscous fan drive clutch engage. This air flowing through radiator core will cause a reaction to thermostatic spring coil. Fan speed will then increase to provide necessary additional engine cooling.
Regardless of increased engine speed, once the fan reached its maximum operating speed, it will not rotate any faster. When the necessary engine cooling has been accomplished causing a reduction in temperature of radiator discharge air, the spring coil again reacts. This will cause fan speed to be reduced to its previous disengaged speed.