Originally Posted by Kaitain
Ok, the intercooler, the fans, and everything else you guys are talking about has 0 to do with why modern turbo's no longer need a turbo timer to let the oil cool, so as to not cook it within the bearing.
Modern turbos now use water cooling, along with oil cooling to keep the bearings and turbine cool. When you turn the engine off, the water continues to flow throughout to cool off the bearings which in turn keeps the oil from scorching and sticking, since it is no longer flowing. Old turbo's were mianly oil cooled, so letting it run a little while after a hard run, was to let the oil continue to do its job since it was the only way it cooled off.
So, there is no reason to use a turbo timer with a modern oil/water cooled turbine. Enjoy!
The turbo on the N20 is oil-cooled (only), not water-cooled. Google "BMW N20 technical specification" and you can find the very detailed BMW documentation on this engine. The N20 does have an oil cooler (oil-to-coolant heat exchanger) that's separate from the turbo, so I suppose you could say that the turbo is *indirectly* water-cooled, but to call it "water cooled" is miss-leading. I don't know if the N55 turbo is oil-cooled, water-cooled, or both.
To the OP: same as others have suggested, my advice (and practice) is, if you have been driving aggressively (generous use of WOT), drive moderately for the last couple minutes before you park (and shut down).