Characteristic map thermostat

The characteristic map thermostat is also attached to the housing of the coolant pump.

Fig 1: Coolant Temperature Sensor Components

Courtesy of BMW OF NORTH AMERICA, INC.

The wax element of the characteristic map thermostat contains a heater resistor. The Digital Engine Electronics (DME) supplies the heater resistor with current. This causes the wax element to expand and close the cylinder head inlet against the spring pressure of a spring. The spring has the task of pressing the characteristic map thermostat back into its rest position when the wax element cools down. With the engine cold, the coolant circuit runs via the cylinder head inlet and characteristic map thermostat to the return line towards the coolant pump.

The Digital Engine Electronics (DME) activate the heating element via a characteristic map depending on the current driving situation.

Fig 2: Coolant Temperature Graph

Courtesy of BMW OF NORTH AMERICA, INC.