GM Service Manual Online
For 1990-2009 cars only
Makes 🢒 GMC_Truck 🢒 2004 🢒 TopKick C-Series (Conventional) C4/C5 🢒 HVAC 🢒 HVAC Systems - Manual 🢒 Heater Core Replacement

Tools Required

J 38185 Hose Clamp Pliers

Removal Procedure
  1. Drain the engine coolant. Refer to Cooling System Draining and Filling in Engine Cooling.
  2. Remove the right wheel house panel. Refer to Wheelhouse Panel Replacement in Body Front End.
  3. Remove the air cleaner layer. Refer to the appropriate procedure:
    4. •  Air Cleaner Replacement in Engine Controls-6.6L.
    •  Air Cleaner Replacement in Engine Controls-8.1L.
    •  Air Cleaner Replacement in Engine Controls-7.8L.
    •  Air Cleaner Replacement Caterpillar® 3126 Unit Repair Manual
  4. Remove the hose clamps using the J 38185 .
  5. Remove the inlet and outlet heater hoses from the heater core.

    6. Object Number: 301592 Size: SH
  6. Remove the screws from the heater assembly.
  7. CAREFULLY open the heater core access door in order to cut the heater core access door.
  8. Cut the marked section of the heater core access door.

    9. Object Number: 301590 Size: SH
  9. Remove the retainers from the heater core.
  10. Remove the heater core.

Installation Procedure

    Object Number: 301590 Size: SH
  1. Install the heater core.

    2. 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.

  2. Install the heater core retainers.

    3. Tighten
    Tighten the screws to 1.9 N·m (17 lb in).


    Object Number: 301592 Size: SH
  3. Install the heater core access door.
  4. Install the heater core access door retaining screws.

    5. Tighten
    Tighten the screws to 1.9 N·m (17 lb in).

  5. Install the inlet and outlet heater hoses to the heater core.
  6. Install the heater hose clamps using the J 38185 .
  7. Install the right wheel house panel. Refer to Wheelhouse Panel Replacement in Body Front End.
  8. Install the air cleaner layer. Refer to the appropriate procedure:
    9. •  Air Cleaner Replacement in Engine Controls-6.6L.
    •  Air Cleaner Replacement in Engine Controls-8.1L.
    •  Air Cleaner Replacement in Engine Controls-7.8L.
    •  Air Cleaner Replacement Caterpillar® 3126 Unit Repair Manual
  9. Fill the engine coolant. Refer to Cooling System Draining and Filling in Engine Cooling.