Remove and replace the heater core in a 1966 Chevrolet Corvette, requiring removal of the right-side inner fender panel and extensive disassembly of the heater assembly.

Warnings

Tools required

Parts

• Heater core × 1 — Use OEM specification
• Heater core seal/gasket kit × 1 — Use OEM specification
• Heater hose clamps × 4 — Replace as needed
• Coolant hose sections (if deteriorated) × 1 — 5/8" and 3/4" heater hose

Fluids

• DEX-COOL Extended Life (Orange) — 10 qt

Preparation

1. Park vehicle on level surface and allow engine to cool completely (minimum 2 hours after operation).
2. Disconnect negative battery cable.
3. Place protective covering over right front fender and right side interior carpet/floor.
4. Remove right front wheel for improved access to inner fender panel.
5. Locate drain petcock on radiator and position drain pan underneath.

Procedure

1. 1

   Drain cooling system
   Open radiator drain petcock and drain coolant into appropriate container. Once drained, close petcock. Remove radiator cap to ensure complete drainage. If coolant is contaminated or more than 2 years old, plan to refill with fresh coolant rather than reusing.
2. 2

   Remove right inner fender panel
   From wheel well, remove the 12 screws securing the right inner fender panel to the fender and firewall. Carefully pull panel away and set aside. This provides access to the heater assembly mounting area from the engine bay side.
3. 3

   Disconnect heater hoses at firewall
   Locate the two heater hoses at the firewall on the right side of engine bay. Use hose clamp pliers to release clamps and slide them back on hoses. Twist hoses gently to break seal, then pull off the heater core inlet and outlet tubes. Be prepared for residual coolant spillage. Plug hose ends with rags to prevent further draining.
4. 4

   Remove interior center console and radio (if equipped)
   From inside vehicle, remove center console by removing the 4 screws at the base. If radio is installed, disconnect antenna and power leads, then remove radio mounting hardware and slide radio out. This provides access to the heater distribution plenum.
5. 5

   Disconnect heater control cables and electrical connections
   Locate heater control cables connected to the heater assembly beneath the dash. Use pliers to compress cable retaining clips and disconnect cables from temperature and blower door levers. Disconnect the blower motor electrical connector and any other electrical connections to the heater assembly. Label connections for reassembly.
6. 6

   Remove heater distribution duct
   Remove the 6 screws securing the center heater distribution duct to the heater assembly and dash panel. Carefully work the duct free and remove it from the vehicle. This duct directs heated air to the center vents.
7. 7

   Disconnect defroster ducts
   Locate defroster ducts connected to top of heater assembly. Remove the 2 screws at each duct connection point and disconnect ducts. These flexible ducts run to the windshield defroster vents.
8. 8

   Remove heater assembly mounting hardware
   Remove the 5 nuts securing the heater assembly to the firewall. Three nuts are accessible from engine bay side through the inner fender opening, and 2 nuts are accessible from inside the vehicle beneath the dash. Support the heater assembly as you remove the final fasteners.
9. 9

   Remove heater assembly from vehicle
   With all mounting hardware removed, carefully maneuver the heater assembly out from beneath the dash. You may need to tilt and rotate the assembly to clear the steering column and dash structure. Remove assembly through the passenger side. Place assembly on clean workbench with drain pan underneath.
10. 10

    Disassemble heater case and remove heater core
    Place heater assembly on workbench. Remove the 8 screws holding the heater case halves together. Carefully separate case halves, noting the position of all internal baffles, doors, and linkages. Lift heater core out of case. Be prepared for additional coolant spillage. Inspect case for cracks or damage.
11. 11

    Clean heater case and prepare for new core
    Remove all old gasket material and sealer from heater case halves using a razor blade and wire brush. Clean internal surfaces with damp cloth to remove debris and dried coolant residue. Inspect blower motor operation and door mechanisms, lubricating pivot points with light machine oil. Check that all air doors move freely.
12. 12

    Install new heater core
    Position new seals/gaskets on heater core inlet and outlet tubes. Carefully place new heater core into lower case half, ensuring it seats properly in mounting position. Check that core tubes align with case openings and that all seals are properly positioned.
13. 13

    Reassemble heater case
    Position upper case half onto lower half, ensuring all internal doors and linkages are properly aligned and move freely. Install the 8 case screws and tighten evenly in a cross pattern to prevent case warping. Verify air doors still operate smoothly after case assembly.
14. 14

    Reinstall heater assembly in vehicle
    Maneuver heater assembly back into position beneath dash, carefully routing it past steering column. Align mounting studs with firewall holes. Install the 5 mounting nuts (3 from engine bay, 2 from interior) and tighten securely. Ensure assembly is properly seated against firewall.
15. 15

    Reconnect all connections and reinstall components
    Reconnect defroster ducts and secure with screws. Reinstall center distribution duct with 6 screws. Reconnect heater control cables to temperature and blower door levers, ensuring cables are properly seated in retaining clips. Reconnect blower motor electrical connector. Reinstall radio and center console if removed.
16. 16

    Connect heater hoses and reinstall inner fender panel
    From engine bay, slide new hose clamps onto heater hoses. Push hoses firmly onto heater core inlet and outlet tubes, ensuring full engagement. Position clamps over tube connections and tighten securely. Reinstall right inner fender panel with 12 screws. Reinstall right front wheel.
17. 17

    Refill cooling system and bleed air
    Fill radiator slowly with conventional ethylene glycol (green) coolant mixed 50/50 with distilled water to proper level. With radiator cap off, start engine and allow to idle. Set heater controls to maximum heat and maximum blower speed. As engine warms, coolant level will drop as thermostat opens and air bleeds from system. Add coolant as needed to maintain proper level. Continue running until engine reaches operating temperature and heater blows hot air, indicating air purge is complete.
18. 18

    Final checks and pressure test
    With engine at operating temperature, check all heater hose connections for leaks. Install radiator cap and allow engine to reach full operating pressure. Inspect for any coolant seepage at firewall penetrations or hose connections. Check coolant level in overflow tank and top off if needed. Allow engine to cool, then recheck coolant level when cold.

Reassembly

1. Ensure all heater control cables move smoothly through their full range before buttoning up interior trim.
2. Test all heater functions (heat, defrost, blower speeds) before declaring job complete.
3. Monitor coolant level for the first few days of operation as residual air may continue to purge from system.

Verification

• Start engine and verify heater produces hot air at all blower speeds within 10 minutes of engine reaching operating temperature.
• Check that air flow direction changes properly when switching between heat, defrost, and vent modes.
• Verify no coolant leaks at heater hose connections or at firewall penetrations.
• Confirm coolant level remains stable after initial bleeding and top-off.
• Check that no coolant odor is present inside vehicle during operation.

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