perature. It allows the engine to reach normal oper-
ating temperature as quickly as possible, maintains
normal operating temperature and prevents over-
heating.

The cooling system also provides a means of heat-

ing the passenger compartment. The cooling system
is pressurized and uses a centrifugal water pump to
circulate coolant throughout the system. A separate
and remotely mounted, pressurized coolant tank
using a pressure/vent cap is used.

COOLING SYSTEM COMPONENTS

The cooling system consists of:
• Charge Air Cooler

• Electric Cooling Fans

• A aluminum-core radiator with plastic side

tanks

• A separate pressurized coolant tank

• A pressure/vent cap on the coolant tank

• Fan shroud

• Thermostat

• Coolant

• Low coolant warning lamp

• Coolant temperature gauge

• Water pump

• Hoses and hose clamps

DIAGNOSIS AND TESTING

DIAGNOSIS AND TESTING - COOLING SYSTEM

Establish what driving conditions caused the com-

plaint. Abnormal loads on the cooling system such as
the following may be the cause:

(1) PROLONGED IDLE, VERY HIGH AMBIENT

TEMPERATURE, SLIGHT TAIL WIND AT IDLE,
SLOW TRAFFIC, TRAFFIC JAMS, HIGH SPEED
OR STEEP GRADES.

• Idle with A/C off when temperature gauge is at

end of normal range.

(2) TRAILER TOWING:
Consult Trailer Towing section of owners manual.

Do not exceed limits.

(3) RECENT SERVICE OR ACCIDENT REPAIR:
Determine if any recent service has been per-

formed on vehicle that may effect cooling system.
This may be:

• Engine adjustments (incorrect timing)

• Slipping engine accessory drive belt

• Brakes (possibly dragging)

• Changed parts (incorrect water pump)

• Reconditioned radiator or cooling system refill-

ing (possibly under filled or air trapped in system).

NOTE: If investigation reveals none of the previous
items as a cause for an engine overheating com-
plaint, refer to following Cooling System Diagnosis
charts.

These charts are to be used as a quick-reference

only.

COOLING 2.5L TURBO DIESEL

7 - 1

COOLING SYSTEM DIAGNOSIS-DIESEL ENGINE

CONDITION

POSSIBLE CAUSES

CORRECTION

TEMPERATURE GAUGE

READS LOW

1. Diesel engines, due to their
inherent efficiency are slower to
warm up than gasoline powered
engines, and will operate at lower
temperatures when the vehicle is
unloaded.

1. The low gauge reading may
be normal. Refer to thermostats
in the manual text for
information. See Thermostat
Diagnosis-Diesel Engine.

2. Is the temperature gauge
connected to the temperature gauge
coolant sensor on the engine?

2. Check, the engine
temperature sensor connector
in the engine compartment.

3. Is the temperature gauge
operating OK?

3. Check gauge operation.
Repair as necessary.

4. Coolant level low in cold ambient
temperatures accompanied with poor
heater performance.

4. Check coolant level in the
coolant tank. Inspect system for
leaks. Repair leaks as
necessary. Refer to the Coolant
section for WARNINGS and
precautions before removing
the pressure cap.

5. Improper operation of internal
heater doors or heater controls.

5. Inspect heater and repair as
necessary. Refer to Heating
and Air Conditioning for
procedures.

TEMPERATURE GAUGE

READS HIGH. COOLANT

MAY OR MAY NOT BE

LOST OR LEAKING FROM

COOLING SYSTEM

1. Trailer is being towed, a steep hill
is being climbed, vehicle is operated
in slow moving traffic, or engine is
being idled with very high ambient
(outside) temperature and the air
conditioning is on. Higher altitudes
could aggravate these conditions.

1. This may be a temporary
condition and repair is not
necessary. Turn off the air
conditioning and attempt to
drive the vehicle without any of
the previous conditions.
Observe the temperature
gauge. The gauge should return
to the normal range. If the
gauge does not return to
normal range, determine the
cause for the overheating and
repair.

2. Temperature gauge reading
incorrectly.

2. Check gauge. Refer to I/P
group.

3. Coolant low in coolant tank and
radiator.

3. Check for coolant leaks and
repair as necessary.

4. Pressure cap not installed tightly.
If cap is loose, boiling point of
coolant will be lowered.

4. Tighten cap.

5. Poor seals at pressure/vent cap.

5. (a) Check condition of cap
and cap seals. (b) Check
condition of coolant tank filler
neck. Make sure it does not
leak pressure.

7 - 2

COOLING 2.5L TURBO DIESEL

COOLING 2.5L TURBO DIESEL (Continued)

CONDITION

POSSIBLE CAUSES

CORRECTION

6. Freeze point of antifreeze not
correct. Mixture may be too rich.

6. Check antifreeze. Adjust
antifreeze-to-water ratio as
required.

7. Coolant not flowing through
system.

7. Check for coolant flow in
coolant tank with engine warm
and thermostat open. Coolant
should be observed flowing
through the tank. If flow is not
observed, determine reason for
lack of flow and repair as
necessary.

8. Radiator or A/C condenser fins
are dirty or clogged.

8. Clean debris from radiator or
A/C condenser

9. Radiator core is corroded or
plugged.

9. Have radiator re-cored or
replaced.

10. Aftermarket A/C installed without
proper A/C condenser.

10. Install proper A/C
condenser.

11. Dragging Brakes.

11. Check and correct as
necessary.

12. Non-factory bug screen is being
used reducing air flow.

12. Only a factory screen
should be used.

13. Thermostat partially or
completely shut. This is more
prevalent on high mileage vehicles.

13. Check thermostat and
replace if necessary.

14. Cylinder head gasket leaking.

14. Check cylinder head gasket
for leaks.

15. Heater core leaking.

15. Check heater core for
leaks. Repair as necessary.

TEMPERATURE GAUGE

READING IS

INCONSISTENT

(FLUCTUATES, CYCLES

OR IS ERRATIC)

1. During cold weather operation,
with the heater blower in the high
position, the gauge reading may
drop slightly. Fluctuation is also
influenced by loads, outside
temperature and extended idle time
with diesel engines.

1. A normal condition. No
correction is necessary.

2. Temperature gauge or engine
mounted gauge sensor defective or
shorted. Also, corroded or loose
wiring in this circuit.

2. Check operation of gauge
and repair as necessary.

3. Gauge reading rises when vehicle
is brought to a stop after heavy use
(engine still running).

3. A normal condition. No
correction needed. Gauge
should return to normal range
after vehicle is driven.

4. Gauge reading high after starting
a warm-up (hot) engine.

4. A normal condition. No
correction needed. Gauge
should return to normal after a
few minutes of engine
operation.

COOLING 2.5L TURBO DIESEL

7 - 3

COOLING 2.5L TURBO DIESEL (Continued)

CONDITION

POSSIBLE CAUSES

CORRECTION

5. Coolant level low in the coolant
tank (air will build up in the cooling
system causing the thermostat to
open late).

5. Check and correct coolant
leaks.

6. Cylinder head gasket leaking
allowing exhaust gases to enter the
cooling system causing the
thermostat to open late.

6. (a) Check for cylinder head
gasket leaks with a
commercially available leak
tester. (b) Check for coolant in
engine oil. Inspect for white
steam emitting from exhaust
system. Repair as necessary.

7. Water pump impeller loose on
shaft.

7. Check water pump and
replace as necessary.

8. Loose accessory drive belt (water
pump slipping).

8. Check and correct as
necessary.

9. Air leak on the suction side of the
water pump allowing air to build up
in the cooling system causing the
thermostat to open late.

9. 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 TANK

1. Pressure relief valve in pressure/
vent cap is defective.

1. Check condition of
pressure/vent cap and cap
seals.

2. Head gasket leak or cracked
cylinder head.

2. Repair as necessary.

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 cooling system
and repair as necessary.

HOSE OR HOSES

COLLAPSE WHEN

ENGINE IS COOLING

1. Vacuum created in cooling system
on engine cool-down is not being
relieved through pressure/vent cap.

1. Cap relief valve stuck.
Replace if necessary.

NOISY FAN

1. Cooling fan blades loose.

1. Replace cooling fan
assembly.

2. Cooling fan blades striking a
surrounding object.

2. Locate point of fan blade
contact and repair as
necessary.

3. Air obstructions at radiator or A/C
condenser.

3. Remove obstructions or
clean debris from radiator or
A/C condenser.

7 - 4

COOLING 2.5L TURBO DIESEL

COOLING 2.5L TURBO DIESEL (Continued)

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