Thermostat Monitoring

Thermostat Monitoring

General Description Of Thermostat Monitoring
Task of the coolant thermostat is to effect a quick engine warm up after start. The thermostat is closed after engine start to limit the cooling-liquid circulation until the thermostat regulating temperature is reached. The thermostat opens at this temperature and the limitation of the cooling-liquid circulation is finished. If an opened stuck thermostat occurs, the cooling-liquid circulation will not be limited after start. That means an increase of the engine warm up time and can cause emission increase as well.

To monitor the thermostat function, a modelled value for coolant temperature is used. This monitoring is only used for diagnosing a thermostat stuck in the open position. The actual coolant temperature is compared to the modelled coolant temperature, When the modelled temperature has reached normal operating temperature it is then compared to the actual coolant temperature. If there is a large discrepancy the thermostat is declared stuck open.