Water Pump: Description and Operation

Electric Auxiliary Water Pump

The new Turbo is equipped with an electric auxiliary water pump which is installed on the left under the intake manifold. This pump can be activated as required by the DME control unit (also when the ignition is switched off) for the purpose of coolant circulation and in order to cool the watercooled turbochargers.

There are three conditions for auxiliary water pump activation:
1. Defined pump operation after engine start. 10 seconds after the engine is started, the pump runs for 10 seconds. This guarantees that the pump starts after every engine start, and therefore allows final stage diagnosis to be performed.
2. Support of cooling in an applied range during engine operation. The pump is switched on when the engine speed is less than 2,000 rpm and the water temperature is greater than 208 °F (98 °C). It is switched off as soon as the engine speed exceeds 2,500 rpm or if the water temperature falls to below 203 °F (95 °C). Since both switch-on conditions are linked, it is sufficient if one condition is not satisfied for the pump to be switched off.
3. Cooling during control unit after running after the engine is switched off or stalled. The higher of the two exhaust temperatures is sent through a low pass filter with a filter time constant of 256 seconds. This filtered exhaust temperature value and the water temperature are the input variables which are evaluated in the DME control unit. On the basis of this information, the DME control unit calculates as the output variable the pump after-run time (function of engine temperature and filtered exhaust temperature) in seconds. The pump after-run time may be between 0 to 600 seconds, depending on the engine temperature (185 °F/84.8 °C to 248 °F/120 °C) and exhaust temperature (1,260 °F/700 °C to 1,922 °F/1,050 °C).

The engine oil temperature is routed through a different low-pass filter with a filter time constant of 64 seconds. This filtered engine oil temperature value and the water temperature represent the input variables for a different map. Output variable: Pump after-run time (function of engine water temperature and filtered engine oil temperature) in seconds.

The pump after-run time may be between 0 to 600 seconds, depending on the engine temperature (194 °F/90 °C to 248 °F/120 °C) and engine oil temperature (194 °F/90 °C to 302 °F/150 °C).

Example: The after-run time is 300 seconds for an oil temperature of 248 °F (120 °C) and a water temperature of 194 °F (90 °C). The engine compartment temperature and ambient temperature do not have any effect on these functions.