Characteristic map thermostat

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

Fig 1: Identifying Coolant Pump Components

Courtesy of BMW OF NORTH AMERICA, INC.

Index	Explanation
1	Characteristic map thermostat
2	two-pin plug connection
3	Coolant temperature sensor
4	Coolant pump

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: Digital Engine Electronics Characteristic Graph

Courtesy of BMW OF NORTH AMERICA, INC.

Index	Explanation
1	Heater resistor not activated
2	Heater resistor activated
3	Time
4	Coolant temperature