GM Service Manual Online
For 1990-2009 cars only

Thermostat Housing Crossover Replacement 6.6L (LB7) Engine

Removal Procedure

  1. Disconnect the battery negative cable. Refer to Battery Negative Cable Disconnection and Connection in Engine Electrical.
  2. Drain the engine coolant. Refer to Cooling System Draining and Filling .
  3. Remove the upper fan shroud. Refer to Fan Shroud Replacement .
  4. Remove the drive belt. Refer to Drive Belt Replacement in Engine Mechanical - 6.6L.

  5. Object Number: 652573  Size: SH
  6. Disconnect the A/C compressor clutch electrical connector.
  7. Disconnect the A/C cut out switch electrical connector.
  8. Remove the A/C compressor mounting bolts.
  9. Move the A/C compressor with the hoses attached to the right side of the engine compartment.

  10. Object Number: 666693  Size: SH
  11. Remove the nut retaining the generator positive cable to the generator.
  12. Remove the positive cable from the generator.
  13. Remove the clip holding the positive cable to the engine front cover.
  14. Remove the bolt retaining the battery positive cable junction block to the power steering pump.
  15. Move the generator positive cable and the junction block bracket aside.
  16. Disconnect the generator electrical connector.
  17. Disconnect the engine coolant temperature (ECT) sensor electrical connector.

  18. Object Number: 669241  Size: SH
  19. Remove the power steering pump mounting bracket and secure to the side. Refer to Air Conditioning (A/C) Compressor and Power Steering Pump Bracket Replacement .
  20. • Do not remove the power steering pump from the bracket.
    • The hoses and battery cables can remain on the power steering pump.

    Object Number: 698198  Size: SH
  21. Remove the bolts retaining the fuel bleed valve and PCV oil separator bracket from the generator mounting bracket.

  22. Object Number: 669244  Size: SH
  23. Remove the heater outlet hose bracket bolt from the generator bracket.
  24. Remove the ribbed idler pulley.
  25. Remove the generator mounting bracket and secure to the side.
  26. • The generator does not require removal.
    • The drive belt tensioner does not require removal.
  27. Remove the oil fill tube. Refer to Oil Filler Tube Replacement in Engine Mechanical - 6.6L.
  28. Remove the water outlet tube. Refer to Water Outlet Tube Replacement .

  29. Object Number: 699325  Size: SH
  30. Remove the bolt retaining the heater pipe to the fuel filter assembly.
  31. Remove the bolt retaining the heater pipe to the thermostat housing crossover.
  32. Remove the heater pipe with O-ring seal from the crossover.

  33. Object Number: 699335  Size: SH
  34. Remove the hose and clamp from the turbocharger outlet coolant pipe to thermostat bypass pipe.
  35. Remove the fuel line bracket from the thermostat housing crossover.
  36. Remove the cooling fan pulley. Refer to Cooling Fan Pulley Replacement .

  37. Object Number: 654526  Size: SH
  38. Remove the 2  thermostat housing crossover bolts and 2 nuts from the left cylinder head.
  39. Remove the 2 thermostat housing crossover bolts and 2 nuts from the right cylinder head.
  40. Remove the bypass pipe to water pump bolts.
  41. Remove the thermostat housing crossover with the bypass pipe.
  42. Remove the bypass pipe to water pump O-ring.

  43. Object Number: 660428  Size: SH
  44. Remove the bypass pipe from the thermostat housing crossover.
  45. Remove the O-ring from the bypass pipe.

Inspection and Repair Procedure


    Object Number: 660424  Size: SH
  1. If required, remove the thermostat cover bolts.
  2. Remove the thermostat cover.
  3. Remove the thermostats with seals.
  4. Remove the thermostat seals.
  5. Remove the ECT sensor if replacing the thermostat housing crossover.

  6. Object Number: 663758  Size: SH
  7. Clean the water crossover.
  8. Clean the thermostat housing crossover mating surfaces.
  9. Inspect the thermostat housing crossover for cracks.
  10. Inspect the thermostat housing crossover mating surfaces for damage.
  11. Replace the thermostat housing crossover if any damage is found.

  12. Object Number: 660424  Size: SH
  13. Install the thermostats with the seals.
  14. The thermostat with the vent valves goes toward the rear of the engine. Install with the vent valves towards the rear of the engine.

  15. Install the thermostat cover and gasket.
  16. 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.

  17. Install the thermostat cover bolts.
  18. Tighten
    Tighten the thermostat cover bolts to 21 N·m (15 lb ft).

  19. If removed, install the ECT sensor.
  20. Tighten
    Tighten the ECT sensor to 33 N·m (24 lb ft).

Installation Procedure


    Object Number: 660428  Size: SH
  1. Install a new O-ring to the bypass pipe. Lubricate the O-ring with coolant.
  2. Install the bypass pipe to the thermostat housing crossover.

  3. Object Number: 654526  Size: SH
  4. Install new thermostat crossover gaskets.
  5. Install a new O-ring for the bypass pipe to the water pump.
  6. Install the thermostat crossover with the bypass pipe.
  7. 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.

  8. Install the bypass pipe to water pump bolts.
  9. Tighten
    Tighten the bypass pipe to water pump bolts to 21 N·m (15 lb ft).

  10. Install the thermostat crossover bolts and nuts.
  11. Tighten
    Tighten the thermostat crossover bolts and nuts to 21 N·m (15 lb ft).

  12. Install the fuel line bracket and bolt.
  13. Tighten
    Tighten the fuel line bracket bolt to 21 N·m (15 lb ft).


    Object Number: 699335  Size: SH
  14. Install the hose and clamp from the turbocharger outlet coolant pipe to thermostat bypass pipe.
  15. Install the cooling fan pulley. Refer to Cooling Fan Pulley Replacement .

  16. Object Number: 699325  Size: SH
  17. Install a new O-ring seal to the heater pipe.
  18. Install the heater pipe to the thermostat housing crossover.
  19. Install the bolt retaining the heater pipe to the thermostat housing crossover.
  20. Tighten
    Tighten the heater pipe bolt to 21 N·m (15 lb ft).

  21. Install the bolt retaining the heater pipe to the fuel filter assembly.
  22. Tighten
    Tighten the heater pipe bracket bolt to 21 N·m (15 lb ft).


    Object Number: 669244  Size: SH
  23. Install the generator mounting bracket and bolts.
  24. Tighten
    Tighten the generator mounting bracket bolts to 50 N·m (37 lb ft).

  25. Install the ribbed idler pulley and the bolt.
  26. Tighten
    Tighten the idler puller bolt to 43 N·m (32 lb ft).

  27. Install the heater outlet hose bracket bolt.
  28. Tighten
    Tighten the bracket bolt to 21 N·m (15 lb ft).


    Object Number: 698198  Size: SH
  29. Install the nuts retaining the fuel bleed valve and PCV oil separator bracket from the generator mounting bracket.
  30. Tighten
    Tighten the bracket nuts to 25 N·m (18 lb ft).


    Object Number: 669241  Size: SH
  31. Install the power steering pump mounting bracket and bolts. Refer to Air Conditioning (A/C) Compressor and Power Steering Pump Bracket Replacement .
  32. Tighten
    Tighten the power steering pump mounting bracket bolts to 46 N·m (34 lb ft).

  33. Install the water outlet tube. Refer to Water Outlet Tube Replacement .

  34. Object Number: 666693  Size: SH
  35. Position the generator positive cable.
  36. Install the generator positive cable in the clip on the engine front cover.
  37. Install the generator positive cable and the retaining nut to the generator.
  38. Tighten
    Tighten the generator positive cable nut to 9 N·m (80 lb in).

  39. Install the battery positive cable junction block bracket and bolt to the power steering pump.
  40. Tighten
    Tighten the junction block bracket bolt to 9 N·m (80 lb in).

  41. Connect the generator electrical connector.

  42. Object Number: 652573  Size: SH
  43. Position the A/C compressor.
  44. Install the A/C compressor mounting bolts.
  45. Tighten
    Tighten the A/C compressor mounting bolts to 50 N·m (37 lb ft).

  46. Connect the A/C cut out switch electrical connector.
  47. Connect the A/C clutch electrical connector.
  48. Install the drive belt. Refer to Drive Belt Replacement in Engine Mechanical - 6.6L.
  49. Install the upper fan shroud. Refer to Fan Shroud Replacement .
  50. Fill the engine coolant. Refer to Cooling System Draining and Filling .
  51. Connect the battery negative cable. Refer to Battery Negative Cable Disconnection and Connection in Engine Electrical.

Thermostat Housing Crossover Replacement 6.6L LLY

Removal Procedure

  1. Remove the air cleaner. Refer to Air Cleaner Replacement for the 6.6L ( LLY) engine .
  2. Drain the cooling system. Refer to Cooling System Draining and Filling .
  3. Disconnect the negative battery cables. Refer to Battery Negative Cable Disconnection and Connection .
  4. Remove the charge air pipe from the charge air cooler and the air intake tube. Refer to Charged Air Cooler Hoses/Pipes Replacement for the 6.6L (LLY) engine.
  5. Remove the upper fan shroud. Refer to Fan Shroud Replacement .
  6. Remove the drive belt. Refer to Drive Belt Replacement for the 6.6L (LLY) engine.
  7. Disconnect the air conditioning (A/C) compressor clutch electrical connector.
  8. Disconnect the A/C cut out switch electrical connector.

  9. Object Number: 769156  Size: SH
  10. Remove the A/C compressor bolts (1).
  11. Reposition the A/C compressor (3), with the hoses attached, to the right side of the engine compartment.

  12. Object Number: 1395836  Size: SH
  13. Remove the generator positive cable to generator nut.
  14. Remove the positive cable from the generator.
  15. Unclip the engine wiring harness retainer and remove the engine wiring harness from the retainer.
  16. Remove the engine wiring harness clamp nut at the air intake pipe.
  17. Remove the nut, bolt and the 2 wiring harness brackets and reposition the engine wiring harness.

  18. Object Number: 1335413  Size: SH
  19. Disconnect the engine coolant temperature (ECT) sensor electrical connector.

  20. Object Number: 798057  Size: SH
  21. Without disconnecting the power steering hoses, remove the power steering pump bolts and the power steering pump. Reposition the power steering pump and secure to the side. Refer to Power Steering Pump Replacement .
  22. Remove the power steering pump bracket. Refer to Air Conditioning (A/C) Compressor and Power Steering Pump Bracket Replacement for the 6.6L (LLY) engine.

  23. Object Number: 669244  Size: SH
  24. Remove the heater outlet hose bracket bolt from the generator bracket.
  25. Remove the ribbed idler pulley.
  26. Remove the generator bracket bolts.
  27. Remove the generator bracket and position to the side.
  28. • The generator does not require removal.
    • The drive belt tensioner does not require removal.
  29. Remove the front oil fill tube. Refer to Oil Filler Tube Replacement for the 6.6L (LLY) engine.
  30. Remove the water outlet. Refer to Water Outlet Tube Replacement .

  31. Object Number: 1335419  Size: SH
  32. Reposition the exhaust gas recirculation (EGR) hose clamp at the EGR coolant pipe.
  33. Remove the EGR coolant pipe bolt.
  34. Remove the EGR coolant pipe with O-ring seal from the crossover.

  35. Object Number: 1335429  Size: SH
  36. Reposition the turbocharger coolant return pipe hose clamp.
  37. Remove the turbocharger coolant return pipe hose.

  38. Object Number: 1335434  Size: SH
  39. Remove the fuel line bracket bolt at the thermostat housing crossover.
  40. Remove the cooling fan pulley. Refer to Cooling Fan Pulley Replacement .

  41. Object Number: 1335424  Size: SH
  42. Remove the water pump inlet pipe bolts.

  43. Object Number: 1335441  Size: SH
  44. Remove the thermostat housing crossover bolts and nuts.
  45. Remove the thermostat housing crossover, with the bypass pipe.
  46. Remove and discard the thermostat bypass pipe to water pump O-ring seal.
  47. Remove and discard the thermostat housing crossover gaskets.

  48. Object Number: 660424  Size: SH
  49. If necessary, perform the following:
  50. 37.1. Remove the thermostat bypass pipe from the thermostat housing crossover.
    37.2. Remove and discard the thermostat bypass pipe O-ring seal.
    37.3. Remove the thermostat cover bolts and cover.
    37.4. Remove the thermostats.
    37.5. Remove and discard the thermostat seals.
  51. If required, clean and inspect the thermostat housing. Refer to Engine Coolant Thermostat Housing Cleaning and Inspection for the 6.6L (LLY) engine.

Installation Procedure

    Notice: Refer to Fastener Notice in the Preface section.


    Object Number: 660424  Size: SH
  1. If necessary, perform the following:
  2. 1.1. Install NEW seals to the thermostats.
    1.2. Install the thermostats.
    1.3. Install the thermostat cover and bolts.

    Tighten
    Tighten the bolts to 21 N·m (15 lb ft).

    1.4. Install a NEW O-ring seal to the thermostat bypass pipe.
    1.5. Install the thermostat bypass pipe to the thermostat housing.

    Object Number: 1335441  Size: SH
  3. Install a NEW thermostat bypass pipe to water pump O-ring seal.
  4. Install the thermostat housing crossover using NEW gaskets.
  5. Install the thermostat housing crossover bolts and nuts.
  6. Tighten
    Tighten the bolts/nuts to 21 N·m (15 lb ft).


    Object Number: 1335424  Size: SH
  7. Install the water pump inlet pipe bolts.
  8. Tighten
    Tighten the bolts to 21 N·m (15 lb ft).

  9. Install the cooling fan pulley. Refer to Cooling Fan Pulley Replacement .

  10. Object Number: 1335434  Size: SH
  11. Install the fuel line bracket bolt at the thermostat housing crossover.
  12. Tighten
    Tighten the bolt to 21 N·m (15 lb ft).


    Object Number: 1335429  Size: SH
  13. Install the turbocharger coolant return pipe hose.
  14. Position the turbocharger coolant return pipe hose clamp.

  15. Object Number: 1335419  Size: SH
  16. Install the EGR coolant pipe with O-ring seal to the crossover.
  17. Install the EGR coolant pipe bolt.
  18. Tighten
    Tighten the bolt to 25 N·m (18 lb ft).

  19. Position the EGR hose clamp at the EGR coolant pipe.
  20. Install the water outlet. Refer to Water Outlet Tube Replacement .
  21. Install the front oil fill tube. Refer to Oil Filler Tube Replacement for the 6.6L (LLY) engine.

  22. Object Number: 669244  Size: SH
  23. Position the generator bracket.
  24. Install the generator bracket bolts.
  25. Tighten
    Tighten the bolt to 50 N·m (37 lb ft).

  26. Install the ribbed idler pulley.
  27. Tighten
    Tighten the bolt to 43 N·m (32 lb ft).

  28. Install the heater outlet hose bracket bolt to the generator bracket.
  29. Tighten
    Tighten the bolt to 21 N·m (15 lb ft).

  30. Install the power steering pump bracket to the engine. Refer to Air Conditioning (A/C) Compressor and Power Steering Pump Bracket Replacement for the 6.6L (LLY) engine.
  31. Install the power steering pump. Refer to Power Steering Pump Replacement .

  32. Object Number: 1395836  Size: SH
  33. Install the positive cable to the generator.
  34. Install the generator positive cable to generator nut.
  35. Tighten
    Tighten the nut to 9 N·m (80 lb in).


    Object Number: 1335413  Size: SH
  36. Connect the ECT sensor electrical connector.
  37. Connect the generator electrical connector.

  38. Object Number: 769156  Size: SH
  39. Position the A/C compressor (3), with the hoses attached.
  40. Install the A/C compressor bolts (1).
  41. Tighten
    Tighten the bolts to 50 N·m (37 lb ft).

  42. Connect the A/C cut out switch electrical connector.
  43. Connect the A/C compressor clutch electrical connector.
  44. Position the engine wiring harness to the retainer and secure the retainer.
  45. Install the engine wiring harness brackets and clamps to the thermostat housing and the air intake pipe with nut and bolt.
  46. Tighten
    Tighten the nut and bolt to 25 N·m (18 lb ft).

  47. Install the drive belt. Refer to Drive Belt Replacement for the 6.6L (LLY) engine.
  48. Install the upper fan shroud. Refer to Fan Shroud Replacement .
  49. Connect the negative battery cables. Refer to Battery Negative Cable Disconnection and Connection .
  50. Install the air cleaner. Refer to Air Cleaner Replacement for the 6.6L (LLY) engine.
  51. Fill the cooling system. Refer to Cooling System Draining and Filling .