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