Page 181 - Automobile Mechanical and Electrical Systems Automotive Technology Vehicle Maintenance and Repair (Vehicle Maintenance Repr Nv2) by Tom Denton

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Engine systems 165

Figure 2.169 Viscous-fan hub on an earlier engine

Figure 2.170 Viscous-fan hub

Figure 2.171 Motor-driven fan

remains closed and the clutch is inoperative. When the air fl ow temperature over
the viscous hub increases, the valve in the hub opens and the viscous fl uid is
driven outwards by centrifugal force. The increased force in the fl uid locks the
plates in the hub together to engage the clutch drive to the fan.

An improved temperature-sensing arrangement is for the fan to be driven by an
electric motor mounted on a cowl frame attached to the radiator ( Fig. 2.171 ). A
plastic fan is fi tted to the motor spindle and operates when a temperature-sensitive
switch closes. The electrical supply to the motor is connected through a relay.