This procedure covers removal and replacement of the coolant bypass pipe on the 1966 Chevrolet Corvette 327ci V8 engine, which routes coolant between the water pump and intake manifold.

Warnings

Tools required

Parts

• Coolant bypass pipe × 1 — Use OEM specification
• Bypass pipe gaskets × 2 — Use OEM specification
• Hose clamps (if deteriorated) × 2 — Worm gear type, appropriate size

Fluids

• DEX-COOL Extended Life (Orange) — 3 qt

Preparation

1. Ensure engine is completely cold to the touch
2. Position drain pan under radiator petcock
3. Disconnect negative battery cable to prevent accidental fan engagement
4. Remove air cleaner assembly for better access to upper engine area

Procedure

1. 1

   Drain cooling system
   Open the radiator petcock at the bottom of the radiator and drain coolant into the drain pan. If the petcock is seized, carefully remove the lower radiator hose at the radiator instead. Drain until coolant level is below the height of the bypass pipe on the engine block.
2. 2

   Remove upper radiator hose if necessary
   If the upper radiator hose restricts access to the bypass pipe, loosen the hose clamp at the intake manifold and slide the hose off. This is typically required for easier access on small block Chevys with factory air conditioning.
3. 3

   Disconnect bypass hose
   Locate the short rubber bypass hose connecting the water pump housing to the bypass pipe. Use pliers to squeeze and slide the hose clamps away from the connection points. Twist and pull the hose off both the water pump and the bypass pipe. Inspect the hose for deterioration and replace if cracked or swollen.
4. 4

   Remove bypass pipe mounting bolts
   The bypass pipe is secured to the front of the intake manifold and the engine block with 2 bolts. Remove both bolts using the appropriate socket. The pipe may also have a bracket or support tab. Keep all fasteners organized for reinstallation.
5. 5

   Remove bypass pipe assembly
   Carefully work the bypass pipe away from the intake manifold and block. The pipe may be stuck due to gasket sealing or corrosion. Gently twist and pull to break the seal. Avoid using excessive force that could damage the mating surfaces on the intake manifold or block.
6. 6

   Clean mating surfaces
   Use a gasket scraper and wire brush to remove all old gasket material from both the intake manifold and engine block mating surfaces where the bypass pipe seals. Ensure surfaces are completely clean and free of debris. Wipe clean with shop rags.
7. 7

   Inspect new bypass pipe
   Compare the new bypass pipe to the old unit to verify correct routing and mounting hole alignment. Check that new gaskets are included and match the sealing surfaces. Inspect the pipe for any shipping damage or manufacturing defects.
8. 8

   Install new gaskets
   Position new gaskets on both ends of the bypass pipe. The gaskets should fit snugly over the pipe ends. Some installers prefer to use a small amount of gasket sealer on metal-to-metal surfaces, though this is not required with new gaskets on clean surfaces.
9. 9

   Install bypass pipe assembly
   Carefully position the bypass pipe assembly so both ends align with their respective mounting locations on the intake manifold and engine block. Start both mounting bolts by hand to ensure proper thread engagement before tightening.
10. 10

    Torque mounting bolts
    Tighten both bypass pipe mounting bolts evenly to 15 ft-lbs. Alternate between bolts to ensure even seating of the gaskets. Do not overtighten as this can distort the pipe or crack the gasket.
11. 11

    Reconnect bypass hose
    Slide the bypass hose onto both the water pump connection and the bypass pipe. Ensure the hose is pushed fully onto both connections. Position the hose clamps over the hose ends and tighten securely. The clamps should be positioned approximately 1/2 inch from the hose ends.
12. 12

    Reinstall upper radiator hose
    If the upper radiator hose was removed in step 2, reinstall it now. Push the hose fully onto the intake manifold connection and secure with the hose clamp.
13. 13

    Refill cooling system
    Close the radiator petcock or reinstall the lower radiator hose if it was removed. Fill the radiator with conventional green ethylene glycol (IAT) coolant mixed to appropriate freeze protection (typically 50/50 mix with distilled water). Fill slowly to allow air to escape. Add coolant until the radiator is full.
14. 14

    Bleed cooling system
    With the radiator cap still off, start the engine and allow it to warm up to operating temperature. Watch the coolant level in the radiator and add coolant as the thermostat opens and air purges from the system. Carefully squeeze the upper radiator hose to help release trapped air. Continue until no more air bubbles emerge and the coolant level stabilizes.

Reassembly

1. Reinstall air cleaner assembly
2. Reconnect negative battery cable
3. Double-check all hose clamps are tight and all connections are secure

Verification

• With engine at operating temperature, inspect all connections around the bypass pipe for coolant leaks
• Verify coolant level is correct in the radiator and remains stable after test drive
• Check for proper heater operation, which confirms coolant flow through the bypass circuit
• Monitor temperature gauge during test drive to ensure normal operating temperature is maintained

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