Hummer H1 (2006+). Manual - part 185

4-20

Cooling System

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LOW COOLANT SENSOR 

The coolant level sensor is a solid-state semi-conductor device. The sensor’s resistance varies as a function of its temperature. As
voltage/current flows through the sensor, sensor temperature increases. In the presence of a liquid, in this case engine coolant, the
temperature of the sensor is controlled by transferring heat to the coolant. Should the coolant level drop below the sensor, the heat
and resistance of the sensor will rise. The “Low Coolant” warning light will then illuminate in response to the increased resistance
at the sensor. 

Removal

1.

Drain and collect the coolant from the surge tank. 

2.

Disconnect the low coolant sensor electrical connector from the engine harness connector. 

3.

Remove the sensor and the O-ring from the surge tank (Figure  4-16).

Figure 4-16:   Low Coolant Sensor

Installation

1.

Position the O-ring on the sensor and thread the sensor into the surge tank (Figure  4-16). 

2.

Plug the low coolant sensor electrical connector into the engine harness connector.

3.

Fill the surge tank with coolant. See cooling system service for proper filling and bleeding procedure.

ELECTRICAL

LOW 

O-RING

 CONNECTOR

COOLANT

SENSOR

 TANK

SURGE

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 Cooling System  4-21

5745804

THERMOSTAT REPLACEMENT

Removal

1.

Disconnect the battery.

2.

Drain the engine coolant below the level of the water crossover.

3.

Disconnect the transmission control harness connector behind the AC compressor and remove the harness mount bracket.

4.

Remove the charge air pipe above the engine harness connector.

5.

Disconnect the engine harness connector and the harness mount bracket.

6.

Release the serpentine belt.

7.

Remove the P clip securing the AC lines.

8.

Remove the AC compressor and set aside with the AC lines still connected.

9.

Remove the water outlet pipe.

10. Remove the thermostat cover (Figure  4-17).

11. Remove both of the thermostats (Figure  4-17).

Installation

1.

Install the thermostats and seals into the water crossover pipe (Figure  4-17).

NOTE: The rear thermostat has 2 vent valves. Install with the vent valves towards the rear of engine (Figure  4-17).

WARNING:  Damage to the thermostats and the housing can occur if the thermostats are not installed properly.

2.

Install the thermostat cover and tighten the cover bolts to15 lb ft (21 N·m).

3.

Fill and bleed the cooling system. See cooling system service for proper filling and bleeding procedure.

4.

Install the water outlet pipe.

5.

Install the AC compressor and secure the AC line with the P clip.

6.

Install the serpentine belt.

7.

Install the engine harness mount bracket and connect the engine harness connector.

8.

Install the charge air pipe.

9.

Install the transmission control harness bracket and connect the transmission control harness connector.

10. Connect the battery.

4-22

Cooling System

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Figure 4-17:   Thermostat and Cover Removal and Installation

WATER PUMP 

Removal

1.

Disconnect the battery.

2.

Drain the engine coolant.

3.

Release and remove the serpentine drive belt.

4.

Remove the large center idler pulley.

5.

Remove the geared fan drive shaft and coupler (Figure  4-18).

6.

Remove the water bypass tube.

7.

Remove the starter.

8.

Remove the crank shaft damper bolt using the flywheel lock J-44643 and remove the crank shaft damper.

9.

Remove the water pump inlet hose at the water pump.

10. Remove the front propshaft from the front axle.

11. Remove the water pump to engine water pipe nuts (Figure  4-19). 

12. Remove the water pump assembly from the engine block (Figure  4-19).

THERMOSTAT

HOUSING

GASKETS

WATER

 CROSSOVER

FRONT THERMOSTAT

REAR THERMOSTAT

VENT VALVES

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 Cooling System  4-23

5745804

Figure 4-18:   Geared fan drive shaft

Installation

1.

Lubricate the water pump O-ring with engine oil.

2.

Install the engine water pipe gasket and water pump O-ring on the water pump.

3.

Install the water pump and the water pump bolts tighten the bolts to 15 lb ft (21 N·m) (Figure  4-19).

NOTE: Make sure the correct length bolt is used in the proper location.

4.

Install the water pump to engine water pipe nuts tighten the nuts to 15 lb ft (21 N·m) (Figure  4-19).

5.

Install the crank shaft damper and bolt tighten to 260 lb ft (353 N·m).

6.

Install the starter tighten the bolts to 58 lb ft (78 N·m).

7.

Install the water pump inlet hose at the water pump.

8.

Install the front propshaft to the front axle.

9.

Install the water bypass tube.

10. Install the geared fan drive shaft and the coupler (Figure  4-18).

GEARED FAN

DRIVE SHAFT

COUPLER