Turbo Cool down Air cooled vs Water cooled vs Oil

[SuffolkD at aol.com]

Hope I haven't started a torsen thread.
Phil:
I'm not sure about your post RE: the air flow cooling.
Audi plumbs so much around the turbo side of the 1.8/2.7, 3B and 10V (MC & 
MC2) that I just can't see much air flow contributing to turbo cool down.  I do 
agree that any RAM air over the block is helpful for under hood temps, that's 
why we "cool down" the last lap on a track, mostly for brakes but hey for the 
turbo guys too.....

Audi does have the ("water") afterrun pump (AFAIK on at least the MC's & 
3B/AAN I-5's) which handles the circulation of coolant after the motor is shut 
down.

But Phil, the Oil just sits there (albeit dripping into the pan elsewhere by 
gravity) after shut down.  Its the passages around the turbo I'm concerned 
with, those temps will soar due to heat soak around the turbo shaft and those 
bearings.  Its that HIGH ~100,000 RPM shaft which needs to be play free and 
smoothly balanced, is where I see coking to be an issue on a just shut down turbo 
engine.
A little sludge or mineral build up there is detrimental to the longevity of 
the turbo. IMHO

For the truly paranoid popping the hood would be the best transfer of heat 
from that area in a parking of the vehicle situation.
Most "tracked cars" perform this ritual (at least street cars at DE and club 
events.)
Cool air from under the car, by convection, will carry heat from that turbo 
and manifold area into the atmosphere.
However, in daily driving, popping the hood at the mall or in a parking spot 
just isn't practical on several other levels like vandalism or theft.

I guess my point is don't spool up the turbo and work the engine hard just to 
quickly shut it down seconds to two minutes later....
-Scott by BOSTON

> > Steve, good point regarding cooling down the turbo. I generally sit in my
> > driveway for about 45 seconds to a minute (depending on the amount of time
> > I have driven the car) and at least wait for the turbo to spool down (I
> > can hear it doing that if I have been driving for a while and/or driving
> > hard) - then wait a bit longer.
> From: "Phil Payne" <>
> EXACTLY the wrong thing to do.
> 
> Despite all the crap about oil-cooled turbos and water-cooled turbos, all 
> Audi turbos are
> actually air-cooled.  Oil has almost no cooling effect, and serious water 
> flow through the
> later models' water jackets (only around the bearing) doesn't start until 
> some time after the
> ignition has been switched off.
> 
> You need airflow to cool the turbo, and there is no airflow if the car is 
> stationary - except
>