December 6th, 2011, 23:01
Factory Turbotimer ? :)
Continued coolant circulation pump -V51-
The electric continued coolant circulation pump -V51- is fitted underneath the intake manifold. When the engine is switched off, it prevents coolant in the turbochargers (which are still hot) from boiling.
The Motronic current supply relay -J271- is active for 15 minutes above an engine temperature of 60 °C after the engine is switched off, and also powers the continued coolant circulation relay -J151- in addition to the engine control unit. The earth supply to the relay coil comes from terminal 61 of the alternator, which conducts earth only when the engine is stopped.
The object of this circuitry is that the continued coolant circulation relay -J151- operates the electric continued coolant circulation pump -V51- for at least 15 minutes only above an engine temperature of 60 °C when the engine is stopped. When the engine is running circulation is handled by the mechanical coolant pump alone.
December 6th, 2011, 23:27
Audi has been doing something similar since at least the early '90s. On the early S cars (5 cyl turbo) there is an electric pump as well, except in that case it is activated by a relay triggered by a dedicated temperature sensor. That relay also engages the electric radiator fan. It only rarely comes on though.
Thanks for that writeup though, it confirms what I found in the wiring diagrams (and wrote about in my recent afterrun thread). Where is that text from?
In the RS6 there is also a coolant circulation valve, which changes position based on whether the ignition is on or not.
December 7th, 2011, 15:24
This text is from my service manual