Engine cooling

The map thermostat opens and closes, regulated by a characteristic map. This regulating operation can be split into 3 operating ranges:

• Engine cold, map thermostat closed:

  The coolant only flows in the engine (short circuit). The coolant circuit is closed. The thermostat is not activated.

• Engine hot, map thermostat open:

  The entire volume of coolant flows via the radiator. This results in maximum use of the available cooling power. The characteristic map thermostat is not activated.

• Control range of the map thermostat:

  Part of the coolant flows through the radiator. The map thermostat opens as of 105 °C and maintains a constant coolant temperature. In this operating range, the map thermostat can now be used to influence the coolant temperature specifically.

  • Economy mode: 108 °C
  • Normal mode: 104 °C
  • High mode: 95 °C
  • High mode and control operation by characteristic map thermostat: 90 °C.
• This enables the setting of a higher coolant temperature in the partial load range of the engine. At higher operating temperatures in the part-load range, friction is reduced. This in turn leads to reduced consumption and pollutant emissions. During full load operation, certain disadvantages are associated with higher operating temperatures (ignition advance reduction due to knocking combustion). A lower coolant temperature is therefore specifically set during full load operation with the assistance of the characteristic map thermostat.

The following illustration shows the operating principle of the engine cooling.

Fig 1: Engine Cooling System Diagram

Courtesy of BMW OF NORTH AMERICA, INC.