Jeep 1997 Grand Cherokee Service Manual page 243

ZG
DIAGNOSIS AND TESTING (Continued)
CONDITION
TEMPERATURE GAUGE READS HIGH OR
ENGINE COOLANT WARNING LAMP
ILLUMINATES. COOLANT MAY OR MAY
NOT BE LOST OR LEAKING FROM
COOLING SYSTEM
TEMPERATURE GAUGE READING IS
INCONSISTENT (FLUCTUATES, CYCLES
OR IS ERRATIC)
PRESSURE CAP IS BLOWING OFF STEAM
AND/OR COOLANT TO COOLANT TANK.
TEMPERATURE GAUGE READING MAY BE
ABOVE NORMAL BUT NOT HIGH.
COOLANT LEVEL MAY BE HIGH IN
COOLANT RESERVE/OVERFLOW TANK
COOLANT LOSS TO THE GROUND
WITHOUT PRESSURE CAP BLOWOFF.
GAUGE IS READING HIGH OR HOT
POSSIBLE CAUSES
9. Coolant not flowing through system.
10. Radiator or A/C condenser fins are dirty
or clogged.
11. Radiator core is corroded or plugged.
12. Fuel or ignition system problems.
13. Dragging brakes.
14. Bug screen is being used reducing
airflow.
15. Thermostat partially or completely shut.
This is more prevalent of high mileage
vehicles.
16. Thermal viscous fan drive not operating
properly.
17. Cylinder head gasket leaking.
18. Heater core leaking.
1. During cold weather operation, with the
heater blower in the high position, the gauge
reading may drop slightly.
2. Temperature gauge or engine mounted
gauge sensor defective or shorted. Also,
corroded or loose wiring in the circuit.
3. Gauge reading rises when vehicle is
brought to a stop after heavy use (engine
still running).
4. Gauge reading high after restarting a
warmed-up (hot) engine.
5. Coolant level low in radiator (air will build
up in the cooling system causing the
thermostat to open late).
6. Cylinder head gasket leaking allowing
exhaust gas to enter cooling system causing
thermostat to open late.
7. Water pump impeller loose on shaft.
8. Loose accessory drive belt (water pump
slipping).
. Air leak on the suction side of water pump
allows air to build up in cooling system
causing thermostat to open late.
1. Pressure relief valve in radiator cap is
defective.
1. Coolant leaks in radiator, cooling system
hoses, water pump or engine.
COOLING SYSTEM
CORRECTION
9. Check for coolant flow at radiator filler
neck with some coolant removed, engine
warm and thermostat open. Coolant should
be observed flowing through radiator. If flow
is not observed, determine reason for lack of
flow and repair as necessary.
10. Clean insects or debris. Refer to Radiator
Cleaning in this group.
11. Have radiator re-cored or replaced.
12. Refer to Fuel and Ignition System groups
for diagnosis. Also refer to the appropriate
Powertrain Diagnostic Procedures service
manual for operation of the DRB scan tool.
13. Check and correct as necessary. Refer to
Group 5, Brakes in the manual text.
14. Remove bug screen.
15. Check thermostat operation and replace
as necessary. Refer to Thermostats in this
group.
16. Check fan drive operation and replace if
necessary. Refer to Viscous Fan Drive in this
group.
17. Check for cylinder head gasket leaks.
Refer to Testing Cooling System for Leaks in
this group. For repair, refer to Group 9,
Engines.
18. Check heater core for leaks. Refer to
Group 24, Heating and Air Conditioning.
Repair as necessary.
1. A normal condition. No correction is
necessary.
2. Check operation of gauge and repair if
necessary. Refer to Group 8E, Instrument
Panel and Gauges.
3. A normal condition. No correction is
necessary. Gauge reading should return to
normal range after vehicle is driven.
4. A normal condition. No correction is
necessary. The gauge should return to
normal range after a few minutes of engine
operation.
5. Check and correct coolant leaks. Refer to
Testing Cooling System for Leaks in this
group.
6. (a) Check for cylinder head gasket leaks
with a commercially available Block Leak
Tester. Repair as necessary.
(b) Check for coolant in the engine oil.
Inspect for white steam emitting from exhaust
system. Repair as necessary.
7. Check water pump and replace as
necessary. Refer to Water Pumps in this
group.
8. Refer to Engine Accessory Drive Belts in
this group. Check and correct as necessary.
9. Locate leak and repair as necessary.
1. Check condition of radiator cap and cap
seals. Refer to Radiator Caps in this group.
Replace cap as necessary.
1. Pressure test and repair as necessary.
Refer to Testing Cooling System for Leaks in
this group.
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