The coolant temperature sensor is a thermistor where as the coolant temperature increases or decreases, the resistance inside the sensor unit changes accordingly. The coolant sensors' resistance changes inversely as the temperature of the coolant changes. The resistance in the sender unit increases as the fluid temperature decreases and vice versa. When the engine is cold, the resistance of the sender unit is approximately 130 ohms. As the engine warms up to operating temperature, the resistance inside the sender gradually and smoothly decreases to a minimum resistance of 26.7 ohms. At 180° the resistance level is approximately 48.5 ohms.
Depending on the production year, model and trim level, the coolant information gathered by the sensor is relayed to either an idiot light'' or gauge in the instrument cluster or a gauge in the center of the dash panel.
- Remove the coolant temperature sensor from the engine block.
- Clean any residue from the sensor probe.
Attach an ohmmeter to the sensor unit as follows:
- Attach one lead to the metal body of the sensor unit (near the sender unit's threads).
- Attach the other lead to the sensor unit's wiring harness connector terminal.
- With the leads still attached, place the sensor unit in a pot of ice water, such that none of the leads are immersed in the water. The probe section of the sensor unit which normally makes contact with the engine coolant should be submerged.
- Measure the resistance. The resistance should be 98-130 ohms.
- Slowly heat the pot up (on the stove) and observe the resistance. The resistance should evenly and steadily decrease as the water temperature increases. The resistance should not jump decrease erratically.
- When the water reaches 190-210° F (88-99° C) the resistance of the sensor unit should be on, or near, 39-26.7 ohms.
- If the sensor unit did not function as described, replace the sensor.
REMOVAL & INSTALLATION
See Figures 1 and 2
- Disconnect the wire at the sending unit.
- Drain the cooling system to a level below the sending unit.
- Unscrew the sender.
- Coat the threads of the new sender with sealer and screw it into place. Tighten the sender to 15 ft. lbs. (20 Nm).
- Connect the wire.
- Fill the cooling system.