Thermostats The thermostats role in engine management is vital. A thermostat that has failed in the open position will make your heater appear not to work for an extended period of time during winter. If it fails in the closed position it will surely cause your cars engine to overheat leading to costly repairs or ultimately “complete engine failure”. Dayco thermostats are designed to OEM specifications and come with a heat sensing wax filled copper power pill that detects the coolant temperature in the engine. The Dayco thermostats amazing heat sensing power pill controls coolant flow from the radiator when the engine is cold to reach optimum operating temperature quickly. It then allows coolant to circulate through the engine when operating temperature is reached to create the perfect temperature controlled engine environment.