Replace the coolant temperature sensor on a 1966 Chevrolet Corvette 327ci V8 to restore accurate engine temperature readings and proper cooling system operation.

Warnings

Tools required

Parts

• Coolant temperature sensor × 1 — Use OEM specification for 1966 Corvette 327 V8

Fluids

• DEX-COOL Extended Life (Orange) — 1 qt

Preparation

1. Ensure engine is completely cool to the touch (wait at least 2 hours after last operation).
2. Park vehicle on level ground and engage parking brake.
3. Locate coolant temperature sensor on driver's side cylinder head (typically forward of spark plug #1 or #3).
4. Place drain pan beneath sensor location to catch coolant spillage.
5. Disconnect negative battery cable to prevent electrical shorts and erroneous fault codes.

Procedure

1. 1

   Access the coolant temperature sensor
   Locate the coolant temperature sensor on the driver's side cylinder head. On the 1966 327 V8, it is typically positioned in the front section of the head, threaded into a water jacket passage. The sensor has a single wire terminal on top. Trace the wire from the temperature gauge sending unit to confirm correct sensor identification (not to be confused with other thermal switches).
2. 2

   Disconnect sensor electrical connection
   Disconnect the single wire terminal from the top of the coolant temperature sensor. On 1966 models, this is typically a push-on spade connector. Pull the connector straight off the sensor terminal with gentle rocking motion if tight. Inspect connector for corrosion or damage.
3. 3

   Drain coolant to below sensor level
   Remove the radiator cap slowly to relieve any residual pressure. Open the radiator petcock or remove the lower radiator hose to drain coolant until the level drops below the sensor mounting location. You do not need to drain the entire system, only enough to prevent excessive spillage when removing the sensor (approximately 2-3 quarts). Position drain pan to catch coolant.
4. 4

   Remove old coolant temperature sensor
   Using the appropriate deep socket (typically 5/8" or 13/16" depending on sensor hex size), carefully unscrew the coolant temperature sensor from the cylinder head. Turn counterclockwise. Expect some coolant to drain from the opening once the sensor is removed. Have shop rags ready to catch spillage. Remove sensor completely and set aside.
5. 5

   Inspect and clean sensor opening
   Inspect the threaded opening in the cylinder head for debris, corrosion, or damaged threads. Use a wire brush to clean the threads if necessary. Ensure the sealing surface around the opening is clean and free from old sealant or gasket material. Check that coolant passages are not blocked.
6. 6

   Prepare new sensor for installation
   Apply a thin coat of conductive (electrically conductive) sealant to the threads of the new coolant temperature sensor, since this sender grounds through the threads to the head. Do not apply sealant to the first 2 threads to prevent contamination of the cooling system. Avoid getting sealant on the sensor tip, as this can affect temperature readings.
7. 7

   Install new coolant temperature sensor
   Thread the new sensor into the cylinder head by hand to ensure proper thread engagement and prevent cross-threading. Once hand-tight, use the socket and ratchet to snug the sensor firmly into place. Tighten to a snug fit (hand-tight plus approximately 1/4 turn). Do not overtighten, as this can crack the sensor body or damage the cast-iron cylinder head threads.
8. 8

   Reconnect electrical connection
   Push the wire terminal connector firmly onto the new sensor terminal until it seats completely. Ensure the connection is secure and will not vibrate loose during operation. Route the wire away from exhaust manifolds and moving components.
9. 9

   Refill cooling system
   Close the radiator petcock or reinstall the lower radiator hose if it was removed. Refill the cooling system with fresh conventional ethylene glycol (green) coolant mixed 50/50 with distilled water to the proper level. Fill slowly to minimize air pockets. Fill to approximately 1 inch below the radiator filler neck with cap off.
10. 10

    Bleed air from cooling system
    With the radiator cap still off, start the engine and allow it to warm up to operating temperature. Watch the coolant level and add coolant as needed when the thermostat opens and air bleeds from the system. Observe the temperature gauge to ensure it begins reading correctly. Run engine until cooling fan cycles or upper radiator hose becomes hot, indicating full circulation.
11. 11

    Check for leaks and verify operation
    With engine at operating temperature, inspect the area around the new sensor for any coolant leaks. If seepage is observed, shut off engine, allow to cool, and re-tighten sensor slightly. Verify temperature gauge is now reading normally (typically around 180-195°F at operating temperature). Shut off engine, allow to cool slightly, then install radiator cap securely.

Reassembly

1. Reconnect negative battery cable.
2. Check coolant level in radiator when cold and top off if necessary to proper level.
3. Inspect ground beneath vehicle for any coolant drips after first drive cycle.

Verification

• Start engine and verify temperature gauge begins to rise steadily as engine warms up.
• Confirm gauge reads in normal operating range (middle of gauge, approximately 180-195°F).
• Check for any coolant leaks around sensor after engine reaches operating temperature.
• Test drive vehicle and monitor temperature gauge for proper readings under load.
• Recheck coolant level after vehicle has cooled completely and top off if needed.

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