The thermostat limits the flow of coolant through the engine, helping the engine to reach operating temperature quicker. After thousands of heat cycles, the plastic in these units will disintegrate, leading to cracked and leaking housings. The thermostat itself can also often become stuck in one position, resulting in engine overheating or running too cool. This relatively inexpensive item should be on everyone’s list of items to replace every few years, so as to maintain optimum performance. This thermostat from Wahler can be sold at a fraction of the dealership cost without compromising on the quality.