The cooling system is designed to keep every part of
the engine at appropriate temperature in whatever
condition the engine may be operated. The cooling
method is of the water-cooled, pressure forced circu-
lation type in which the water pump pressurizes cool-

ant and circulates it throughout the engine. If the
coolant temperature exceeds the prescribed temper-
ature, the thermostat opens to circulate the coolant
through the radiator as well so that the heat
absorbed by the coolant may be radiated into the air.
The water pump is of the centrifugal type and is
driven by the drive belt from the crankshaft. The radi-
ator is the corrugated fin, down flow type and is
cooled by the cooling fan.

SPECIAL TOOL

M1141000600149

ENGINE COOLING DIAGNOSIS

INTRODUCTION

M1141005300295

The system cools the engine so that it does not over-
heat and maintains the engine at an optimum tem-
perature. The system components are the radiator,
water pump, thermostat, cooling fan and fan clutch
assembly. Possible faults include low coolant, con-
tamination, belt loosening and component damage.

TROUBLESHOOTING STRATEGY

M1141005200298

Use these steps to plan your diagnostic strategy. If
you follow them carefully, you will be sure to find
most of the engine cooling faults.
1. Gather information from the customer.

2. Verify that the condition described by the

customer exists.

3. Find the malfunction by following the Symptom

Chart.

4. Verify that the malfunction is eliminated.

SYMPTOM CHART

M1141005600296

TOOL

TOOL NUMBER AND
NAME

SUPERSESSION

APPLICATION

MB991871
LLC changer

General service tool

Coolant refilling

MB991871

SYMPTOMS

INSPECTION PROCEDURE

REFERENCE PAGE

Coolant Leak

P.14-3

Engine Overheating

P.14-3

ENGINE COOLING DIAGNOSIS

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ENGINE COOLING

14-3

SYMPTOM PROCEDURES

INSPECTION PROCEDURE 1: Coolant Leak

DIAGNOSIS

STEP 1. Check for coolant leaks.

WARNING

When pressure testing the cooling system, slowly
release cooling system pressure to avoid getting
burned by hot coolant.

CAUTION

• Be sure to completely clean away any moisture from

the places checked.

• When the tester is removed, be careful not to spill any

coolant.

• When installing and removing the tester and when test-

ing, be careful not to deform the filler neck of the radia-
tor.

Check that the coolant level is up to the filler neck. Install a radi-
ator tester and apply 160 kPa (23 psi) pressure, and then check
for leakage from the radiator hose or connections.
Q: Is leakage present from the radiator hose or

connections?
YES : Repair or replace the appropriate part, then go to

Step 2.

NO : There is no action to be taken.

STEP 2. Retest the system.
Q: It there still coolant leakage?

YES : Return to Step 1.
NO : The procedure is complete.

INSPECTION PROCEDURE 2: Engine Overheating

DIAGNOSIS

STEP 1. Remove the radiator cap and check for coolant
contamination.
Q: Is the coolant contaminated with rust and oil?

YES : Replace it. Refer to

P.14-5

NO : There is no action to be taken. Go to Step 2.

ACX01844 AB

CAP ADAPTER

ADAPTER

ENGINE COOLING DIAGNOSIS

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ENGINE COOLING

14-4

STEP 2. Check the radiator cap valve opening pressure.
NOTE: Be sure that the cap is clean before testing. Rust or
other foreign material on the cap seal will cause an improper
reading.
(1) Use a cap adapter to attach the cap to the tester.
(2) Increase the pressure until the gauge indicator stops

moving.

Minimum limit: 83 kPa (12 psi)
Standard value: 93

− 123 kPa (14 − 18 psi)

Q: Does the reading remain at or above the minimum limit?

YES : Go to Step 3.
NO : Replace the radiator cap. Then go to Step 5.

STEP 3. Check thermostat operation.
Refer to

P.14-14

Q: Does the thermostat operate correctly?

YES : Go to Step 4.
NO : Replace the thermostat, then go to Step 5.

STEP 4. Check the drive belt for slippage or damage.
Refer to GROUP 00, Maintenance Service

− Drive Belts

(Check Condition)