Low Coolant Level- Aeration; Belt Diagnosis - Jeep 1997 Grand Cherokee Service Manual

ZG
DIAGNOSIS AND TESTING (Continued)
INTERNAL LEAKAGE INSPECTION
Remove the oil pan drain-plug and drain a small
amount of engine oil. Coolant, being heavier will
drain first, or operate engine to churn oil, then exam-
ine dipstick for water globules. Operate the engine
without the pressure/vent cap on the coolant tank
until thermostat opens.
Attach a radiator pressure tester to the tank filler
neck. If pressure builds up quickly, a leak exists as
result of a faulty cylinder head gasket or crack in the
engine. Repair as necessary.
WARNING: DO NOT ALLOW
EXCEED 117 KPA (17 PSI). TURN THE ENGINE OFF.
TO RELEASE THE PRESSURE, ROCK THE TESTER
FROM SIDE TO SIDE. WHEN REMOVING THE
TESTER, DO NOT TURN THE TESTER MORE THAN
1/2 TURN IF THE SYSTEM IS UNDER PRESSURE.
If there is no immediate pressure increase, pump
the pressure tester until the indicated pressure is
within the system range. Vibration of the gauge
pointer indicates compression or combustion leakage
into the cooling system.

LOW COOLANT LEVEL- AERATION

CAUTION: Engine damage could occur if the cool-
ant level is allowed to get this low. Always ensure
that the coolant level is not below the add coolant
mark. The baffles in the pressurized coolant tank
(degasser bottle) will not allow you to see the fluid
level. Check the coolant level through the pressur-
ized coolant tank. For better visibility of the coolant
level use a shop lamp to light the pressurized cool-
ant tank and look through the pressurized coolant
tank.
If the coolant level in the radiator drops below the
top of radiator core tubes, air will enter the cooling
system.
Low coolant level can cause the thermostat pellet
to be suspended in air instead of coolant. This will
cause the thermostat to open later, which in turn
causes higher coolant temperature. Air trapped in
the cooling system also reduces the amount of coolant
circulating in the heater core resulting in low heat
output.

BELT DIAGNOSIS

small cracks that run across the ribbed surface of the
belt from rib to rib (Fig. 11), are considered normal.
These are not a reason to replace the belt. However,
cracks running along a rib (not across) are not nor-
mal. Any belt with cracks running along a rib must
be replaced (Fig. 11). Also replace the belt if it has
excessive wear, frayed cords or severe glazing.
for further belt diagnosis.
PRESSURE TO
When diagnosing serpentine accessory drive belts,
Refer to the Serpentine Drive Belt Diagnosis chart
Fig. 11 Serpentine Belt Wear Patterns
COOLING SYSTEM 7 - 15