Engine Cooling

Coolant thermostat monitoring

The task of the coolant thermostat is to speed up the engine reaching its operating temperature after starting up. The thermostat is closed after an engine start-up in order to restrict the coolant circulation until the thermostat control temperature has been reached. The thermostat opens at this temperature and the restriction of the coolant circulation is terminated.

If the thermostat jams open, the coolant circulation is not restricted after starting up. This leads to an increase in the engine warm-up period and can also increase exhaust emissions. In order to take account of this consequence, a thermostat that jams when open must be detected. Other diagnostic functions could be inhibited by this and/or the refrigerant might not reach its operating temperature window.

If the thermostat jams when closed, there is a danger that the engine will overheat. The driver is informed in that the coolant-temperature warning lamp lights up. A fault memory entry is created.