GM Service Manual Online
For 1990-2009 cars only
Makes 🢒 GMC_Truck 🢒 1999 🢒 GMC K Pickup - 4WD 🢒 Engine 🢒 Engine Electrical 🢒 Thermostat Housing Crossover Replacement

Removal Procedure
  1. Drain the coolant from the radiator. Refer to Cooling System Draining and Filling .
  2. Remove the compressor. Refer to Air Conditioning Compressor Replacement or Air Conditioning Compressor Replacement in HVAC.
  3. Remove the crankcase depression regulator valve.
  4. Remove the generator upper bracket.
  5. Disconnect the bypass hose.
  6. Disconnect the upper radiator hose. Refer to Radiator Hose Replacement or Radiator Hose Replacement or Radiator Hose Replacement .
  7. Disconnect the heater hose. Refer to Heater Hoses Replacement in HVAC.

    8. Object Number: 64991 Size: SH
  8. Remove the studs and the bolts.
  9. Remove the coolant crossover housing assembly (4) from the vehicle. The thermostats (2) and the coolant outlet (1) attach to the crossover housing assembly, along with the thermostat bypass nipple (5).
  10. Clean the crossover housing sealing surfaces.

Installation Procedure

    Object Number: 64991 Size: SH
  1. Install the new gaskets (3).
  2. Install the coolant crossover housing assembly (4).

    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.

  3. Install the studs and the bolts.

    4. Tighten
    Tighten the studs and the bolts to 42 N·m (31 lb ft).

  4. Connect the heater hose. Refer to Heater Hoses Replacement in HVAC.
  5. Connect the upper radiator hose. Refer to Radiator Hose Replacement or Radiator Hose Replacement or Radiator Hose Replacement .
  6. Connect the bypass hose.
  7. Install the generator upper bracket.
  8. Install the compressor. Refer to Air Conditioning Compressor Replacement or Air Conditioning Compressor Replacement in HVAC.
  9. Install the crankcase depression regulator valve.
  10. Fill the cooling system with coolant. Refer to Cooling System Draining and Filling .
  11. Start the engine. Run the engine, with the surge tank cap removed, until the upper radiator hose becomes hot. This indicates that the thermostat is open.
  12. Attach the surge tank cap to the surge tank. Make sure that the cap arrows line up with the overflow tube.
  13. Inspect the cooling system for leaks.