Replace the coolant temperature sensor on a 1970 AMC Rebel Machine 390ci V8 to restore proper temperature gauge operation and engine management.

Warnings

Tools required

Parts

• Coolant temperature sensor × 1 — Use OEM specification or aftermarket equivalent for 1970 AMC 390

Fluids

• 50/50 Antifreeze/coolant mix — 1 qt

Preparation

1. Ensure the engine is completely cold before beginning work
2. Park vehicle on level surface and engage parking brake
3. Place drain pan under the radiator drain petcock or lower radiator hose
4. Drain coolant until the level is below the temperature sensor location on the intake manifold
5. Disconnect the negative battery cable to prevent electrical shorts

Procedure

1. 1

   Locate the coolant temperature sensor
   The coolant temperature sensor is typically threaded into the intake manifold on the driver's side, near the thermostat housing. On the 390ci engine, it may be positioned between the distributor and the cylinder head. Trace the wire from the temperature gauge sending unit to locate it precisely.
2. 2

   Disconnect the electrical connector
   Locate the wire terminal on the coolant temperature sensor. This is typically a single spade connector that slides onto the sensor terminal. Carefully pull the connector straight off the sensor. If corroded, gently work it back and forth while pulling to avoid breaking the wire.
3. 3

   Remove the old sensor
   Using the appropriate deep well socket (typically 13/16" or 1-1/16" depending on sensor type), carefully unscrew the coolant temperature sensor from the intake manifold. Turn counterclockwise. Be prepared for a small amount of coolant to drain from the opening. Have shop towels ready to catch any spillage.
4. 4

   Clean the sensor mounting hole
   Use a wire brush to clean the threads in the intake manifold where the sensor mounts. Remove any old thread sealant, corrosion, or debris. Wipe the area clean with a shop towel to ensure a proper seal when installing the new sensor.
5. 5

   Prepare the new sensor
   Apply a thin coat of thread sealant rated for coolant use to the threads of the new coolant temperature sensor. Do not apply sealant to the tip of the sensor or the first two threads, as excess sealant could contaminate the cooling system or affect sensor readings.
6. 6

   Install the new sensor
   Thread the new coolant temperature sensor into the intake manifold by hand, turning clockwise. Start it carefully to avoid cross-threading. Once hand-tight, use the socket and ratchet to snug the sensor firmly. Tighten until snug but do not overtighten, as the brass sensor body can crack or the threads in the aluminum intake can strip. Typically 10-15 ft-lbs is sufficient, though tighten by feel to a firm snug fit.
7. 7

   Reconnect the electrical connector
   Slide the electrical connector firmly onto the terminal of the new coolant temperature sensor. Ensure it is fully seated and makes good contact. Tug gently to verify it is secure.
8. 8

   Refill the cooling system
   Close the radiator drain petcock or reconnect the lower radiator hose if removed. Refill the cooling system with the appropriate 50/50 antifreeze and water mixture. Fill the radiator to the proper level and add coolant to the overflow reservoir if equipped.
9. 9

   Bleed air from the system
   With the radiator cap off, start the engine and allow it to warm up to operating temperature. Watch for coolant circulation and add coolant as needed to maintain proper level. The thermostat will open and allow air to escape. Squeeze the upper radiator hose gently to help release trapped air bubbles.

Reassembly

1. Reconnect the negative battery cable
2. Install the radiator cap securely once the system is bled and topped off
3. Check for any coolant leaks around the sensor installation

Verification

• Start the engine and observe the temperature gauge. It should begin to rise as the engine warms up, reaching normal operating temperature range
• Check for coolant leaks around the sensor threads while the engine is running and at operating temperature
• Verify the temperature gauge reads accurately by comparing to actual engine temperature (thermostat should open around 180-195°F)
• Recheck coolant level after the engine has cooled and top off if necessary

More procedures for this vehicle