FAN-RADIATOR VISCOUS
DESCRIPTION
The thermal viscous fan drive (3) is a silicone-fluid-
filled coupling used to connect the fan blades to the
water pump shaft (4). The coupling allows the fan to
be driven in a normal manner. This is done at low
engine speeds while limiting the top speed of the fan
to a predetermined maximum level at higher engine
speeds.
OPERATION
A thermostatic bimetallic spring coil (2) is located on
the front face of the viscous fan drive unit (1). This
spring coil reacts to the temperature of the radiator
discharge air. It engages the viscous fan drive for
higher fan speed if the air temperature from the radi-
ator 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, will the viscous
fan drive engage. This is when the air flowing through
the radiator core causes a reaction to the bimetallic
coil. It then increases fan speed to provide the neces-
sary additional engine cooling.
Once the engine has cooled, the radiator discharge
temperature will drop. The bimetallic coil again reacts
and the fan speed is reduced to the previous disen-
gaged speed.
HB
ENGINE
7 - 47