Hummer H1 (2006+). Manual - part 181

4-4

Cooling System

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ENGINE COOLING SYSTEM DIAGNOSIS AND TROUBLESHOOTING

WARNING:  Do not release the surge tank cap when the engine is hot. The steam and/or the coolant may cause se-
rious injury.

Loss of Coolant

1.

Pressurize the system and check for leaks at all the cooling system hoses.

a.

Tighten the loose clamps, fasteners, and fittings.

b.

Replace the leaking hoses.

2.

Pressurize the coolant system to check for leaks at the water pump or around the cylinder heads. If any leakage is present,
replace the cylinder head gaskets, the cylinder heads, and the water pump.

3.

Check the cylinder block for cracks, and replace it if the cylinder block is cracked.

4.

Check the expansion plugs and the block heater for leaks.

5.

Check the radiator and surge tank.

6.

Remove the surge tank cap. With the engine running, check for excessive bubbles in the surge tank that may indicate a leaking
head gaskets or a cracked cylinder head. If bubbles are present, remove the cylinder heads and check for defective head
gaskets, cracked cylinder heads, or a cracked cylinder block. Replace the cylinder heads if damaged. Replace the engine if
cylinder block is cracked.

Engine Coolant Temperature Gauge In The Red Zone, Engine Overheats

1.

Inspect for low coolant. Verify the low coolant sensor is operating properly. (Refer to Electrical Troubleshooting, Section 12).

WARNING:  Use caution when testing thermostat. Hot engine coolant will cause burns.

NOTE: Off-road driving in extremely dusty conditions may result in debris entrapment between the radiator and oil cooler.
Trapped debris may increase coolant temperature.

2.

Check for a clogged or blocked radiator system. Clean and flush as required. Cleaning requires the separation of the fuel
cooler, AC condensor and oil cooler from the radiator and the fins of all units must be thoroughly flushed with water and
compressed air.

3.

Check the thermostats for proper operation. Remove the thermostats and place the thermostats in a container of water known
to be 190°F (88°C). Observe the valves. If the valves do not open, replace the thermostats. 

4.

Check the radiator for bent fins. Straighten the fins or replace the radiator if it is damaged beyond repair.

5.

Check the operation of the temperature gauge. Refer to Electrical Troubleshooting (Section 12).

6.

Inspect the fan blades for damage. Replace the fan if damaged.

7.

Check the fan clutch (viscous drive) operation.

a.

Check for excessive bearing play. Using fingers only, press tip of fan blade toward and away from the engine. Tip of the
blade total movement should not exceed 0.20 in. (5.1 mm). If the movement is more, replace the fan drive.

b.

With the engine off and an ambient temperature of 50°F (10° C) or higher, the fan should turn evenly with noticeable
drag. If the fan turns hard, very easily, or with uneven resistance, replace the fan drive.

c.

Fan noise is sometimes evident under the following normal conditions:

• When the drive is engaged for maximum cooling.

• During the first 15 seconds to one minute after start-up, until the drive can redistribute the silicone fluid back to its 
    normal disengage operating condition (after overnight settling).

• Fan noise or an excessive roar will generally occur continuously under all engine high speed conditions (2400 RPM 

    and up) if the drive assembly is locked-up due to an internal failure. If the fan cannot be rotated by hand or there is a

rough, grating feel as the fan is turned, replace the fan drive.

8.

Check for a leaking or defective water pump. Replace the leaking or defective water pump.

WARNING:  Do not release surge tank cap when engine is hot. Steam and/or coolant may cause serious injury.

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 Cooling System  4-5

5745804

Fan Runs Continuously (Noisy)

1.

Check that all the fan bolts are present and tightened to 45 lb-ft (61 N•m).

2.

Perform steps 7a and 7b above.

3.

Check for fan cut off (disengagement).

4.

Observe the fan drive disengagement after 1 to 1-1/2 minutes. If fan speed does not drop and coolant temperature remains
below 190° F (88° C), replace the fan drive.

RADIATOR AND FAN SHROUD ASSEMBLY SERVICE

Removal

1.

Remove the hood (Section 10).

2.

Drain the cooling system.

3.

Remove the driver side splash shield.

4.

Remove the battery tray, and the left splash shield. (Sections 10 and 12).

5.

Remove the fuel cooler (Section 3).

6.

If equipped with air conditioning, discharge the system and remove the condenser (Section 11).

7.

Remove the oil cooler (Section 1).

8.

Disconnect the upper hose from the radiator (Figure  4-4).

9.

Disconnect the ambient temperature switch, if equipped (Section 11). 

10. Remove the surge tank.

11. Disconnect the lower radiator hose from the radiator.

12. Remove the lower mount from the radiator and the frame bracket (Figure  4-5).

13. Detach the rear support brackets from the airlift brackets (Figure  4-4). 

14. Remove the radiator and the charge air cooler from the vehicle (Figure  4-5).

15. Remove the charge air cooler from the radiator.

16. Remove the fan shroud from the radiator.

17. Remove the rear support brackets and insulators from the radiator. 

Cleaning and Inspection 

NOTE: Clean all the components, examine for wear or damage, and replace if necessary.

1.

Remove any debris embedded in the radiator fins using water and compressed air (Figure  4-5).

2.

Inspect the radiator for breaks, punctures, cracks, or splits.

3.

Inspect the adapters and the fan shroud.

Installation

1.

Secure the fan shroud to the radiator.

2.

Secure the charge air cooler to the radiator.

3.

Secure the rear support brackets and the insulators to the radiator with the washers and the locknuts. Tighten the locknuts to 26
lb-ft (35 N•m).

4.

Align the radiator with the frame bracket, and the rear support brackets with the airlift brackets (Figures 4-5 ).

5.

Fasten rear support brackets to air lift brackets with bolts, washers, and locknuts. Do not tighten locknuts (Figure  4-4).

4-6

Cooling System

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Figure 4-4:   Radiator and Fan Shroud Assembly Mounting

6.

Attach the lower mount and the radiator to the frame bracket with the washers, and the locknut. Do not tighten (Figure  4-5).

7.

Tighten the rear support bracket locknuts to 26 lb-ft (35 N•m). Tighten the frame bracket bolt to 30 lb-ft (41 N•m)
(Figures 4-4 and 4-5).

8.

Install the strap on the radiator and the shroud (Figure  4-4).

9.

Connect the upper and lower radiator hoses to the radiator.

10. Connect the ambient temperature switch. (Section 11).

11. Install the oil cooler (Section 1).

12. Install the fuel cooler.

13. Install the AC condenser and charge the system (Section 11).

14. Install the surge tank.

15. Connect the surge tank-to-radiator vent hose to the adapter.

16. Fill the cooling system (Section 4).

17. Check all other fluids and fill as necessary.

18. Install the splash shields and battery tray (Section 12).

19. Start the engine and check the cooling system for leaks.

20. Install the hood (Section 10). 

RADIATOR

UPPER RADIATOR HOSE

REAR SUPPORT BRACKET

LOWER RADIATOR HOSE

AIRLIFT BRACKET

ADAPTER

SURGE TANK-TO-RADIATOR VENT HOSE 

FAN SHROUD

STRAP

HOSE FITTING WITH BLEED VALVE

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 Cooling System  4-7

5745804

Figure 4-5:   Radiator and Fan Shroud Assembly Breakdown

RADIATOR

LOWER

MOUNT

FRAME

BRACKET

FAN SHROUD

REAR SUPPORT BRACKET

OIL COOLER

CONDENSER

RIGHT SIDE

AIR LIFT BRACKET

CHARGE AIR

COOLER

FUEL COOLER

T-CASE COOLER

TRANSMISSION

COOLER