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COOLING SYSTEM
7 - 5
COOLING SYSTEM D I A G N O S I S - C O N T I N U E D
Condition and Checks
Diagnosis
(7) Other possible causes.
(7) a — If symptom occurs during high speed operation inspect for
plugged air inlet side of the radiator or condenser,
plugged radiator core tubes, add on A/C package without
proper radiator, engine not operating within specifications,
dragging brakes, trailer towing or hill climbing, or an
insect screen.
b — If symptom occurs during high or low speed operation
inspect for: thermostat being stuck partially open if ambient
temperature is below 70°F and the vehicle has high
mileage, plugged air inlet side of the radiator or
condenser, odd on A/C with incorrect radiator.
c — If symptom occurs during low speed operation only, inspect
the radiator fan drive. Repair as necessary.
TEMPERATURE GAUGE READS HOT. PRESSURE CAP VENTS
RESULTING IN STEAM AND COOLANT TRANSFER TO
COOLANT RESERVE TANK.
(1) Coolant level low in radiator and coolant reserve tank.
(1) a — Fill cooling system and vent trapped air.
b — Inspect for leaks. Repair as necessary,
c — Ensure that pressure cap is completely shut and seals.
d — If level is low in radiator but normal in the coolant reserve
tank, check the filler cap to coolant reserve bottle
connection and pressure cap seal.
(2) Test coolant freeze point.
(2) Adjust coolant to 50/50 mix of anti-freeze and water. Refer to
Coolant section in this group.
(3) Ensure coolant is flowing through system.
(3) a — With the coolant level low and the thermostat open, check
for coolant flow through the radiator at the filler neck.
b — If a metal cracking sound is heard, inspect for core sand
restricting coolant flow through the water jacket and/or a
faulty cylinder head casting.
(4) Thermostat stuck in the closed position (prevalent in cold ambient
temperatures).
(4) Replace thermostat if found to be stuck in closed position. Refer
to the Thermostat Testing section in this group.
(5) Cylinder head gasket leak.
(5) Inspect for leaking cylinder head gasket with a commercially
available Block Leak Tester.
J9007-57
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