This water temperature sensor monitors coolant temperature in the engine cooling circuit and sends a signal to the instrument cluster or engine control unit. It threads into the cylinder head or thermostat housing, where it is directly exposed to coolant flow. A faulty sensor produces an incorrect gauge reading or triggers a warning light, which can mask an actual overheating condition. The sensor uses a 5/8 UNF thread, matching the port in the original housing. On reinstallation, apply thread sealant to the tapered threads and tighten to the specified torque.