Engine cooling
For the cooling system with electric coolant pump, the possibilities of the conventional cooling system are exploited. The heat management determines the current cooling requirement and regulates the cooling system accordingly.
The following components are influenced by the heat management:
- Electric coolant pump
- Characteristic map thermostat
- Digital engine electronics
The cooling power of the system is adapted by means of a freely variable volumetric flow of the coolant.
| Item | Explanation |
|---|---|
| 1 | Radiator |
| 2 | Coolant temperature sensor at radiator outlet |
| 3 | Gearbox oil cooler (integrated in the radiator) |
| 4 | Gearbox oil cooler with thermostat |
| 5 | Characteristic map thermostat |
| 6 | Electric coolant pump |
| 7 | Exhaust turbocharger |
| 8 | Engine |
| 9 | Heat exchanger for heating system |
| 10 | Coolant temperature sensor on engine |
| 11 | Coolant expansion tank |
| 12 | Electric fan |
The heat management determines the current cooling requirement and regulates the cooling system accordingly. Under certain circumstances, the coolant pump can even be switched off completely, for example to accelerate heating of the coolant in the warm-up phase. If the engine is not running but very hot, the coolant pump will also work while the vehicle is out of use. The cooling power can be requested independent of the engine speed.
The heat management now means that, over and above the map thermostat, various characteristic maps can be used for control of the coolant pump. In this way, the engine control unit can adapt the engine temperature to the driving characteristics. The engine control unit (MSD80) regulates the following temperature ranges:
- 108 °C = Economy mode
- 104 °C = Normal mode
- 95 °C = High mode
- 90 °C = High mode and regulation by the characteristic map thermostat
Example: If the engine control unit detects the economical operating range "Economy" due to the driving characteristics, the DME regulates to a higher temperature (108 °C). In this temperature range, the engine is operated with a relatively fuel requirement. The friction inside the engine is reduced at higher temperature. The temperature increase thus favor the lower fuel consumption in the low load range.
In the mode "High and control by the map thermostat", the driver wants to use the optimized power output development of the engine. To allow this, the temperature in the cylinder head is lowered to 90 °C. This reduction leads to better cylinder filling, which increases the torque of the engine. The engine control unit can now regulate to a certain operating range adapted to each driving situation. This means is it possible to influence consumption and power output by means of the cooling system.
Engine oil thermostat
The engine oil thermostat is located at the oil filter.
| Item | Explanation |
|---|---|
| 1 | Engine oil cooler |
| 2 | Bypass |
| 3 | Engine oil thermostat |
| 4 | Engine |
The engine oil thermostat opens or closes depending on the temperature. However, it never closes completely; it has a minimum flow through to the engine oil cooler. Up to an engine oil temperature of 110 °C, the engine oil thermostat is closed. The supplied engine oil flows via the engine oil thermostat back into the oil reverse through the bypass circuit. This ensures faster warming up of the engine. As of an engine oil temperature of 110 °C, the engine oil thermostat opens and reduces the aperture in the short circuit. This increases the oil flow rate in the line to the engine oil cooler. As of approx. 125 °C, the thermostat is fully opened.