Hummer H2. Manual — part 1384

THERMOSTAT DIAGNOSIS

Tools Required

J 24731 Tempil Stick. See Special Tools and Equipment .

Use one of the following procedures in testing for a malfunctioning thermostat.

Thermostat Test Procedure Using Tempil Sticks

The coolant thermostat can be tested using a temperature (tempil) stick. The temperature stick is a pencil like
device. It has a wax material containing certain chemicals which melt at a given temperature. Temperature
sticks can be used to determine a thermostat's operating range, by rubbing 87° C (188° F) and 97° C (206° F)
sticks on the thermostat housing.

1. Use a tempil stick in order to find the opening and the closing temperatures of the coolant thermostat.

z

J 24731 -188 tempil stick melts at 87° C (188° F). The thermostat should begin to open. See
Special Tools and Equipment .

z

J 24731 -206 tempil stick melts at 97° C (206° F). The thermostat should be fully open. See
Special Tools and Equipment .

2. Replace the coolant thermostat if it does not operate properly between this temperature range.

Thermostat Test Procedure Using Glycol

Inspect the operation of the thermostat by hanging the thermostat on a hook in a 50/50 percent solution of DEX-
COOL(R) and clean drinkable water.

In order to inspect if the thermostat valve is opening properly, perform the following test:

19

Overheating .
Is the repair complete?

Go to

Step 22

-

20

Repair the engine internal coolant leak. Refer to Coolant in
Combustion Chamber and Coolant in Engine Oil in Engine
Mechanical - 6.0L.
Is the repair complete?

Go to

Step 22

-

21

Repair or replace the leaking component. Refer to the appropriate
repair.
Is the repair complete?

Go to

Step 22

-

22

Operate the system in order to verify the repair.
Did you find and correct the condition?

System

OK

Go to Step 2

2004 Hummer H2

2004 ENGINE Engine Cooling - Hummer H2

Fig. 3: Thermostat Test Procedure Using Glycol
Courtesy of GENERAL MOTORS CORP.

1. Completely submerge the thermostat in the glycol solution. The solution should be 11° C (22° F) above

the temperature indicated on the thermostat valve.

2. Thoroughly agitate the solution. Under these conditions, the thermostat valve should open.

In order to inspect if the thermostat valve is closing properly, perform the following test:

2004 Hummer H2

2004 ENGINE Engine Cooling - Hummer H2

1. Completely submerge the thermostat in a glycol solution. The solution should be 6° C (10° F) below the

temperature indicated on the thermostat valve.

2. Thoroughly agitate the solution. Under these conditions, the thermostat valve should close completely.

COOLANT HEATER INOPERATIVE

Coolant Heater Inoperative

ENGINE FAILS TO REACH NORMAL OPERATING TEMPERATURE

Engine Fails To Reach Normal Operating Temperature

Step

Action

Yes

No

Connector End View Reference: Cooling System Connector End Views

1

Did you perform the necessary inspections?

Go to

Step 2

Go to Symptoms

- Engine Cooling

2

Test the engine coolant heater power supply cord for an open or short
to ground. Refer to Circuit Testing in Wiring Systems.
Did you find a condition?

Go to

Step 3

Go to Step 4

3

Replace the engine coolant heater power supply cord. Refer to
Coolant Heater Cord Replacement .
Did you complete the repair?

Go to

Step 6

-

4

Inspect for poor connections at the harness connector of the engine
coolant heater. Refer to Testing for Intermittent Conditions and
Poor Connections and Connector Repairs in Wiring Systems.
Did you find and correct the condition?

Go to

Step 6

Go to Step 5

5

Replace the engine coolant heater. Refer to Coolant Heater
Replacement .
Did you complete the repair?

Go to

Step 6

-

6

Operate the system in order to verify the repair.
Did you correct the condition?

System

OK

Go to Step 2

Step

Action

Yes

No

1

Did you review the Symptoms-Engine Cooling diagnostic
information and perform the necessary inspections?

Go to

Step 2

Go to Symptoms -

Engine Cooling

2

Verify that the engine does not reach normal operating
temperature.
Does the engine reach normal operating temperature?

System

OK

Go to Step 3

3

Inspect the coolant level.
Is the coolant level below the add mark?

Go to

Step 4

Go to Step 5

4

1. Add coolant as necessary.

2. Perform a cooling system pressure test.

Does the cooling system hold pressure?

System

OK

Go to Step 5

Inspect for a stuck open, missing, or incorrect thermostat. Refer

2004 Hummer H2

2004 ENGINE Engine Cooling - Hummer H2

PRESSURE CAP TESTING

Tools required

z

J 24460-01 Cooling System Pressure Tester. See Special Tools and Equipment .

z

J 42401 Radiator Cap/Surge Tank Test Adapter. See Special Tools and Equipment .

Pressure Cap Testing

1. Remove the pressure cap.

2. Wash the pressure cap sealing surface with water.

5

to Thermostat Diagnosis .
Is the thermostat operating properly?

System

OK

Go to Step 6

6

Install the correct replacement thermostat. Refer to Thermostat
Housing Replacement
Is the repair complete?

Go to

Step 7

-

7

Run the engine in order to verify the repair.
Does the engine fail to reach normal operating temperature?

-

System OK

CAUTION: To avoid being burned, do not remove the radiator cap or surge tank

cap while the engine is hot. The cooling system will release scalding
fluid and steam under pressure if radiator cap or surge tank cap is
removed while the engine and radiator are still hot.

2004 Hummer H2

2004 ENGINE Engine Cooling - Hummer H2