Engine cooling

The engine cooling system utilizes an electric coolant pump. The heat management determines the current cooling requirement and controls the cooling system accordingly. Under certain circumstances, the coolant pump can be completely switched off, e.g. to rapidly heat up the coolant during the warm-up phase. The coolant pump continues to operate when the hot engine is shut down. The coolant capacity can therefore be varied regardless of the engine speed. In addition to the characteristic map thermostat, the heat management makes it possible to use various characteristic maps for controlling the coolant pump. In this way the engine control unit can adapt the engine temperature to the driving conditions.

The engine control unit regulates the following temperature ranges:

• 108°C/226°F = Economy mode
• 104°C/219°F = Normal mode
• 95°C/203°F = High mode
• 90°C/194°F = High mode and control with characteristic map thermostat

The engine management sets a higher temperature (108°C) when, based on vehicle operation, the engine control unit detects "Economy" mode. The engine is operated with relatively low fuel requirements in this temperature range. The internal engine friction is reduced at higher temperatures. The increase in temperature therefore results in low fuel consumption in the low load range. The driver wishes to utilize the optimum power developed by the engine in "High and control with characteristic map thermostat" mode. For this purpose, the temperature in the cylinder head is reduced to 90°C. This temperature reduction promotes improved volumetric efficiency, thus resulting in an increased engine torque. Adapted to the relevant driving situation, the engine control unit can now regulate a defined operating range. In this way it is possible to influence the fuel consumption and power output through the cooling system.