Design And Function: Thermostat
On engines B4204T9/T10/T11/T12/T15 the thermostat is installed as a complete unit together with the thermostat housing. The thermostat consists of a traditional wax thermostat and an electrically heated heating element. In the wax thermostat's core (in the wax) there is a heating element that is demand controlled by the ECM. This causes the engine temperature to be regulated as required. The thermostat opens in two different ways:
- Traditional opening via the wax element.
- Demand controlled opening via addition of extra heat in the wax element by the electrically heated wax element.
During normal driving, outdoor temperature below approx. 30 °C and with non-activated sport mode, the thermostat opens in the traditional manner at 105 °C. At higher opening temperatures this results in cleaner exhaust gases and lower fuel consumption.
At higher loads, outdoor temperatures above about 30 °C or sport mode selected, the thermostat opens at 90 °C using the heating element. At higher loads, more cooling is required.