Viscous Fan Drive - Jeep 1997 Grand Cherokee Service Manual

7 - 20 COOLING SYSTEM
REMOVAL AND INSTALLATION (Continued)
(4) Do not unbolt fan blade assembly from viscous
fan drive at this time.
Fig. 17 Thermal Viscous Fan Drive and Blade
Assembly
(5) Remove the fan shroud mounting bolts. One of
the bolts is mounted vertically at the bottom of
shroud.
(6) Remove fan shroud and fan blade/viscous fan
drive assembly as a complete unit from vehicle.
(7) After removing fan blade/viscous fan drive
assembly, do not place viscous fan drive in horizon-
tal position. If stored horizontally, silicone fluid in
the viscous fan drive could drain into its bearing
assembly and contaminate lubricant.
CAUTION: Do not attempt to remove the fan pulley
bolts. The fan pulley is under tension from the drive
belt.
(8) Remove four bolts securing fan blade assembly
to viscous fan drive (Fig. 17).
FAN BLADE INSTALLATION
(1) Install fan blade assembly to viscous fan drive.
Tighten bolts (Fig. 17) to 23 N·m (200 in. lbs.) torque.
(2) Position fan shroud and fan blade/viscous fan
drive assembly to vehicle as a complete unit.
(3) Install and tighten fan shroud bolts to 3 N·m
(31 in. lbs.) torque.
(4) Install fan blade/viscous fan drive assembly to
fan pulley shaft (Fig. 17).
(5) Connect negative battery cable.

VISCOUS FAN DRIVE

The thermal viscous fan drive (Fig. 18) is a sili-
cone-fluid-filled coupling. It connects the fan blade
assembly to the fan pulley. 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. A bimetallic spring coil is located on
the front face. This spring coil reacts to the temper-
ature of the radiator discharge air. It engages the
viscous fan drive for higher fan speed if the air tem-
perature 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.
Fig. 18 Viscous Fan Drive
The viscous fan drive will only engage when suffi-
cient heat is present. This is when the air flowing
through the radiator core causes a reaction from the
bimetallic coil. It then increases fan speed to provide
the necessary 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
disengaged speed.
CAUTION: Some engines equipped with serpentine
drive belts have reverse rotating fans and viscous
fan drives. They are marked with the word
REVERSE to designate their usage. Installation of
the wrong fan or viscous fan drive can result in
engine overheating.
NOISE
NOTE: It is normal for fan noise to be louder (roar-
ing) when:
• The underhood temperature is above the engage-
ment point for the viscous drive coupling. This may
ZG