Jeep 1997 Grand Cherokee Service Manual page 238

7 - 10 COOLING SYSTEM
DIAGNOSIS AND TESTING (Continued)
Fig. 16 Impeller Test—Typical
INSPECTING FOR INLET RESTRICTIONS
Inadequate heater performance may be caused by
a metal casting restriction in the water pump heater
hose inlet.
DO NOT WASTE reusable coolant. If solution is
clean, drain the coolant into a clean container for
reuse.
WARNING: DO NOT LOOSEN THE RADIATOR
DRAINCOCK WITH THE SYSTEM HOT AND UNDER
PRESSURE. SERIOUS BURNS FROM THE COOL-
ANT CAN OCCUR.
(1) Drain sufficient coolant from the radiator to
decrease the level below the water pump heater hose
inlet.
(2) Remove the heater hose.
(3) Inspect the inlet for metal casting flash or
other restrictions.
NOTE: Remove the pump from the engine before
removing restriction to prevent contamination of
the coolant with debris. Refer to Water Pump
Removal in this group.
THERMOSTAT
ON-BOARD DIAGNOSTICS
All models are equipped with On-Board Diagnos-
tics for certain cooling system components. Refer to
On-Board Diagnostics (OBD) in the Diagnosis section
of this group for additional information. If the pow-
ertrain control module (PCM) detects low engine cool-
1 INCH 3/16 INCH WELDING 1 1/2 INCHES IMPELLER ROD
9 INCHES
NORMAL NOT NORMAL CRACKS BELT OK CRACKS RELACE BELT
ant temperature, it will record a Diagnostic Trouble
Code (DTC) in the PCM memory. The DTC number
for low coolant temperature is 17. Do not change a
thermostat for lack of heat as indicated by the
instrument panel gauge or heater performance
unless a DTC number 17 is present. Refer to the
Diagnosis section of this group for other probable
causes. For other DTC numbers, refer to On-Board
Diagnostics in Group 25, Emission Control Systems.
The DTC can also be accessed through the DRB
scan tool. Refer to the appropriate Powertrain Diag-
nostic Procedures manual for diagnostic information
and operation of the DRB scan tool.
SERPENTINE DRIVE BELT DIAGNOSIS
When diagnosing serpentine drive belts, small
cracks that run across ribbed surface of belt from rib
to rib (Fig. 17), are considered normal. These are not
a reason to replace belt. However, cracks running
along a rib (not across) are not normal. Any belt
with cracks running along a rib must be replaced
(Fig. 17). Also replace belt if it has excessive wear,
frayed cords or severe glazing.
Refer to the Serpentine Drive Belt Diagnosis
charts for further belt diagnosis.
Fig. 17 Serpentine Accessory Drive Belt
WearPatterns
ZG