GM Service Manual Online
For 1990-2009 cars only

Engine Coolant Thermostat Replacement 8.1L Engine

Removal Procedure


    Object Number: 751425  Size: SH
  1. Drain the cooling system. Refer to Cooling System Draining and Filling .
  2. Reposition the inlet hose clamp at the water outlet.
  3. Remove the inlet hose from the water outlet.

  4. Object Number: 635643  Size: SH
  5. Remove the water outlet bolts (2).
  6. Remove the water outlet (1).
  7. Remove the thermostat (3).

Installation Procedure


    Object Number: 635643  Size: SH
  1. Install the thermostat (3).
  2. Install the water outlet (1).
  3. Notice: Use the correct fastener in the correct location. Replacement fasteners must be the correct part number for that application. Fasteners requiring replacement or fasteners requiring the use of thread locking compound or sealant are identified in the service procedure. Do not use paints, lubricants, or corrosion inhibitors on fasteners or fastener joint surfaces unless specified. These coatings affect fastener torque and joint clamping force and may damage the fastener. Use the correct tightening sequence and specifications when installing fasteners in order to avoid damage to parts and systems.

  4. Install the water outlet bolts (2).
  5. Tighten
    Tighten the water outlet bolts to 30 N·m (22 lb ft).


    Object Number: 751425  Size: SH
  6. Install the inlet hose to the water outlet.
  7. Position the inlet hose clamp at the water outlet.
  8. Fill the cooling system. Refer to Cooling System Draining and Filling .

Engine Coolant Thermostat Replacement 4.3 L Engine

Removal Procedure


    Object Number: 360851  Size: SH
  1. Drain the cooling system. Refer to Cooling System Draining and Filling .
  2. Loosen the air cleaner outlet duct clamp at the mass airflow/intake air temperature (MAF/IAT) sensor.

  3. Object Number: 701705  Size: SH
  4. Remove the positive crankcase ventilation (PCV) hose.

  5. Object Number: 489179  Size: SH
  6. Remove the air cleaner adapter nut.

  7. Object Number: 489176  Size: SH
  8. In order to remove the air cleaner outlet duct, pivot the duct upward until the hinge clip releases from the lip on the throttle body.

  9. Object Number: 367002  Size: SH
  10. Reposition the inlet hose clamp at the water outlet.
  11. Remove the inlet hose from the water outlet.

  12. Object Number: 42901  Size: SH
  13. Remove the water outlet studs.

  14. Object Number: 42895  Size: SH
  15. Remove the water outlet.

  16. Object Number: 42903  Size: SH
  17. Remove the thermostat.
  18. Clean the sealing surface of the water outlet.
  19. Clean the sealing surface of the intake manifold.
  20. Remove and discard the O-ring seal.

Installation Procedure


    Object Number: 42903  Size: SH
  1. Install a NEW O-ring seal to the thermostat.
  2. Install the thermostat.

  3. Object Number: 42895  Size: SH
  4. Install the water outlet.

  5. Object Number: 42901  Size: SH

    Notice: Use the correct fastener in the correct location. Replacement fasteners must be the correct part number for that application. Fasteners requiring replacement or fasteners requiring the use of thread locking compound or sealant are identified in the service procedure. Do not use paints, lubricants, or corrosion inhibitors on fasteners or fastener joint surfaces unless specified. These coatings affect fastener torque and joint clamping force and may damage the fastener. Use the correct tightening sequence and specifications when installing fasteners in order to avoid damage to parts and systems.

  6. Install the water outlet studs.
  7. Tighten
    Tighten the water outlet studs to 25 N·m (18 lb ft).


    Object Number: 367002  Size: SH
  8. Install the inlet hose to the water outlet.
  9. Position the inlet hose clamp at the water outlet.

  10. Object Number: 489176  Size: SH
  11. Align the hinge clip with the lip on the throttle body.
  12. In order to install the air cleaner outlet duct, pivot the air cleaner outlet duct downward until the mounting stud is through the hole.


    Object Number: 489179  Size: SH
  13. Install the air cleaner adapter nut.

  14. Object Number: 701705  Size: SH
  15. Install the PCV hose.

  16. Object Number: 373468  Size: SH
  17. Tighten the air cleaner outlet duct clamp at the MAF/IAT sensor.
  18. Fill the cooling system. Refer to Cooling System Draining and Filling .
  19. Inspect the cooling system for leaks.

Engine Coolant Thermostat Replacement 6.6L Engine

Removal Procedure


    Object Number: 660424  Size: SH
  1. Drain the engine coolant. Refer to Cooling System Draining and Filling .
  2. Remove the water outlet tube. Refer to Water Outlet Tube Replacement .
  3. Remove the bolt for the fuel line bracket.
  4. Remove the 4 bolts retaining the thermostat housing cover.
  5. Remove the 2 thermostats with the seals.

Inspection and Repair Procedure

  1. Inspect the thermostats for sticking, cracks, and leakage of wax.
  2. Replace the thermostats if damage is found.
  3. Clean the thermostat housing and thermostat housing cover sealing surfaces.

Installation Procedure


    Object Number: 654534  Size: SH
  1. Install the 2 thermostats with the seals to the thermostat housing.
  2. The rear thermostat (4) has 2 vent valves. Install with the vent valves towards the rear of engine.


    Object Number: 660424  Size: SH

    Notice: Use the correct fastener in the correct location. Replacement fasteners must be the correct part number for that application. Fasteners requiring replacement or fasteners requiring the use of thread locking compound or sealant are identified in the service procedure. Do not use paints, lubricants, or corrosion inhibitors on fasteners or fastener joint surfaces unless specified. These coatings affect fastener torque and joint clamping force and may damage the fastener. Use the correct tightening sequence and specifications when installing fasteners in order to avoid damage to parts and systems.

  3. Install the thermostat housing cover.
  4. Tighten
    Tighten the thermostat housing cover bolts to 21 N·m (15 lb ft).

  5. Install the fuel line bracket bolt.
  6. Tighten
    Tighten the fuel line bracket and bolt to 21 N·m (1 lb ft).

  7. Install the water outlet tube. Refer to Water Outlet Tube Replacement .
  8. Fill the engine coolant. Refer to Cooling System Draining and Filling .