This water temperature sensor monitors coolant temperature in the engine cooling system and sends a signal to the instrument cluster or engine control unit. It threads directly into the engine block or thermostat housing using an M18 thread, and its resistance changes with coolant temperature to provide a proportional electrical reading. A failed sensor can cause inaccurate temperature gauges, erratic fan operation, or incorrect fuel metering. The original part matches the housing's thread pitch and seal surface, so no adapter or thread sealant is required beyond the specified O-ring or sealing washer. On reinstallation, tighten the sensor to the torque specification for the housing material.