Jeep 1997 Grand Cherokee Service Manual page 244

7 - 16 COOLING SYSTEM
DIAGNOSIS AND TESTING (Continued)
CONDITION
DETONATION OR PRE-IGNITION (NOT
CAUSED BY IGNITION SYSTEM). GAUGE
MAY OR MAY NOT BE READING HIGH
HOSE OR HOSES COLLAPSED WHEN
ENGINE IS COOLING
NOISY FAN
INADEQUATE AIR CONDITIONER
PERFORMANCE (COOLING SYSTEM
SUSPECTED)
INADEQUATE HEATER PERFORMANCE.
THERMOSTAT FAILED IN OPEN POSITION
POSSIBLE CAUSES
1. Engine overheating.
2. Freeze point of antifreeze not correct.
Mixture is too rich or too lean.
1. Vacuum created in cooling system on
engine cool-down is not being relieved
through coolant reserve/overflow system.
1. Fan blades loose.
2. Fan blades striking a surrounding object.
3. Air obstructions at radiator or air
conditioning condenser.
4. Thermal viscous fan drive has defective
bearing.
5. A certain amount of fan noise (roaring)
may be evident on models equipped with a
thermal viscous fan drive. Some of this noise
is normal.
1. Radiator and/or A/C condenser is
restricted, obstructed or dirty (insects, leaves
etc.)
2. Thermal viscous fan drive is free-
wheeling.
3. Engine is overheating (heat may be
transferred from radiator to A/C condenser.
High underhood temperatures due to engine
overheating may also transfer heat to A/C
components).
. Some models with certain engines are
equipped with air seals at the radiator and/or
A/C condenser. If these seals are missing or
damaged, not enough air flow will be pulled
through the radiator and A/C condenser.
1. Has a diagnostic trouble code (DTC)
number 17 been set?
2. Coolant level low.
3. Obstructions in heater hose fittings at
engine.
4. Heater hose kinked.
5. Some models with certain engines are
equipped with a water control valve located
on one of the heater hoses. This valve
maybe defective.
6. Water pump is not pumping water to
heater core. When the engine is fully
warmed up, both heater hoses should be hot
to the touch. If only one of the hoses is hot,
the water pump may not be operating
correctly. The accessory drive belt may also
be slipping causing poor water pump
operation.
CORRECTION
1. Check reason for overheating and repair
as necessary.
2. Check antifreeze. Refer to the Coolant
section of this group. Adjust antifreeze-to-
water ratio as required.
1. (a) Radiator cap relief valve stuck. Refer to
Radiator Cap in this group. Replace if
necessary.
(b) Hose between coolant reserve/overflow
tank and radiator is kinked. Repair as
necessary.
(c) Vent at coolant reserve/overflow tank is
plugged. Clean vent and repair as necessary.
(d) Reserve/overflow tank is interally blocked
or plugged. Check for blockage and repair as
necessary.
1. Replace fan blade assembly. Refer to
Cooling System Fans in this group.
2. Locate point of fan blade contact and
repair as necessary.
3. Remove obstructions and/or clean debris
or insects from radiator or A/C condenser.
4. Replace fan drive. Bearing is not
serviceable. Refer to Viscous Fan Drive in
this group.
5. Refer to Viscous Fan Drive in this group
for an explanation of normal fan noise.
1. Remove restriction and/or clean as
necessary. Refer to Radiator Cleaning in this
group.
2. Refer to Viscous Fan Drive for diagnosis.
Repair as necessary.
3. Correct overheating condition. Refer to text
in Group 7, Cooling.
4. Check for missing or damaged air seals
and repair as necessary.
1. Refer to On-Board Diagnostics in the
manual text and replace thermostat if
necessary.
2. Refer to Testing Cooling System for Leaks
in the manual text. Repair as necessary.
3. Remove heater hoses at both ends and
check for obstructions. Repair as necessary.
4. Locate kinked area and repair as
necessary.
5. Refer to Group 24, Heating and Air
Conditioning for diagnosis. Repair as
necessary.
6. Refer to Water Pumps in this group.
Repair as necessary. If a slipping belt is
detected, refer to Engine Accessory Drive
Belts in this group. Repair as necessary.
ZG