Diagnosis And Testing - Jeep 1997 Grand Cherokee Service Manual

MOUNTING THERMOSTATIC SPRING VISCOUS FAN DRIVE VISCOUS FAN DRIVE NUT TO PUMP HUB WATER
7 - 8 COOLING SYSTEM
DESCRIPTION AND OPERATION (Continued)
Fig. 12 Viscous Fan Drive—4.0L Engine—Typical
Fig. 13 Viscous Fan Drive—5.2/5.9LEngines—
reacts and the fan speed is reduced to the previous
disengaged speed.
CAUTION: 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 overheat-
ing.
CAUTION: If the viscous fan drive is replaced
because of mechanical damage, the 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
fan drive malfunction.
THERMOSTATIC MOUNTING HUB
Typical
SPRING CHECK ENGINE LAMP
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
occur when ambient (outside air temperature) is very
high.
• Engine loads and temperatures are high such as
when towing a trailer.
• Cool silicone fluid within the fan drive unit is
being redistributed back to its normal disengaged
(warm) position. This can occur during the first 15
seconds to one minute after engine start-up on a cold
engine.
LEAKS
Viscous fan drive operation is not affected by small
oil stains near the drive bearing. If leakage appears
excessive, replace the fan drive unit.

DIAGNOSIS AND TESTING

ON-BOARD DIAGNOSTICS (OBD)
FOR CERTAIN COOLING SYSTEM
COMPONENTS
The powertrain control module (PCM) has been
programmed to monitor certain cooling system com-
ponents:
NOTE: If the engine has remained cool for too long
a period, such as with a stuck open thermostat, a
Diagnostic Trouble Code (DTC) number 17 can be
observed at the malfunction indicator lamp. This
lamp is displayed on the instrument panel as the
CHECK ENGINE lamp (Fig. 14).
Fig. 14 Check Engine Lamp Location
ZG