CONDITION
POSSIBLE CAUSES
CORRECTION
7. Water pump impeller loose on
shaft.
7. Check water pump and replace
as necessary. Refer to Water Pump
Removal in this group.
8. Air leak on the suction side of
water pump allows air to build up in
cooling system causing thermostat
to open late.
8. Locate leak and repair as
necessary.
PRESSURE CAP IS BLOWING
OFF STEAM AND/OR COOLANT.
TEMPERATURE GAUGE READING
MAY BE ABOVE NORMAL BUT
NOT HIGH. COOLANT LEVEL MAY
BE HIGH IN COOLANT RESERVE/
OVERFLOW TANK.
1. Pressure relief valve in radiator
cap is defective, or was not
properly seated.
1. Check condition of radiator cap
and cap seal. Refer to Pressure
Cap in this group. Replace cap as
necessary.
2. Incorrect cap was installed.
2. Replace cap as necessary.
3. Incorrect coolant mixture.
3. Make sure a 50% by volume
mixture of coolant is used.
COOLANT LOSS TO THE
GROUND WITHOUT PRESSURE
CAP BLOWOFF. GAUGE IS
READING HIGH OR HOT.
1. Coolant leaks in radiator, cooling
system hoses, water pump or
engine.
1. Pressure test and repair as
necessary. Refer to Testing Cooling
System for Leaks in this group.
DETONATION OR PRE-IGNITION
(NOT CAUSED BY IGNITION
SYSTEM) GAUGE MAY NOT BE
READING HIGH.
1. Engine overheating.
1. Check reason for overheating
and repair as necessary.
2. Freeze point of coolant not
correct. Mixture too concentrated or
too diluted.
2. Check freeze point of the coolant.
Refer to Coolant, General
Information in this section for test
procedure. Adjust the ethylene
glycol to water ration as required.
3. Wrong cooling system pressure
cap.
3. Install correct pressure cap.
HOSE(S) COLLAPSE AS ENGINE
COOLS DOWN.
1. Vacuum created in cooling
system on engine cool-down is not
being relieved through coolant
bottle system.
1. (a) Pressure cap relief valve
stuck. Refer to Pressure cap in this
section. Replace as necessary.
(b) Hose between the pressure and
overflow tank is plugged. Clean vent
and repair as necessary.
(c) Vent at coolant reserve/overflow
tank is plugged. Clean vent and
repair as necessary.
(d) Reserve/overflow tank is
internally blocked. Clean and repair
as necessary.
ELECTRIC RADIATOR FAN RUNS
ALL THE TIME.
1. Fan relay, Powertrain Control
Module (PCM) or engine coolant
temperature sensor defective.
1. Refer to appropriate Powertrain
Diagnostic Manual for operation of
the DRB scan tool. Repair as
necessary.
2. Check for low coolant level.
2. Repair as necessary.
7 - 8
COOLING SYSTEM
300M
DIAGNOSIS AND TESTING (Continued)