[Biturbos4] Turbo failure and after run pumps

[Charles Wurts]

Thanks for the great post Keman, its great to have you as an active 
contributor to this list.  I am a quiet lurker for the most part;  I am 
more active on the V8 list as I seem to spend more time working on my 
older 1990 beast.  I must admit that I am enjoying this list more as 
the signal to noise ratio is increasing with the age of our cars.  I am 
hoping that this trend will continue as the knowledge base builds for 
these great cars and they become less fashionable;  like you I am 
planning to be in this S4 for the long haul.  I am not going to make 
the same mistake with this car that  I did with a 95 UrS4 Avant; sadly 
I sold that one at 100k.


>> would a turbo timer help? does the motronic have one
>> built in?
>
> There isn't a "turbo timer" built-in (one that keeps the engine
> running for a period of time after you turn the ignition key off).
> Car manufacturers don't put this sort of devices in for obvious
> liability reasons.  However, the 2.7T does have an electric
> after-run pump that runs coolant through the engine and turbos
> if the temperature exceeds a certain value.  That sensor has a
> really high trigger point, though; I've never heard mine run.
>
> -Ti
> -- 

I have never heard mine run either Ti.  I thought I would share the 
info that my curiosity on this matter has revealed so far.  Like you 
Ti, I am a long time Audi, and more specifically quattro junky.  For 
those of us who have owned five cylinder turbos from Audi, we all know 
about the after run pumps and fans.  In the eighties and early 
nineties, Audi had incredible success with turbo longevity compared to 
other manufacturers;  I find it hard to believe that they would 
jettison their track record and experience.  As you identified Ti, the 
after run pumps don't kick in until much higher temperatures now in the 
newer Audis with turbos.  I found this a little bit disconcerting and 
pursued the question with a senior member of AWE.  He replied to the 
question by saying that the heat issue with the turbochargers is 
different today than in the earlier years; both oil chemistry and 
metallurgy have come a long way.  More specifically the issue lies in 
the alloys in the turbos ability to retain shape when very hot.  Turbo 
cool down today is less about the coking of the oil in the turbocharger 
and more about the sagging of red hot metal at stand still ( like an 
olympic lifter's barbell.)  He said that as long as you aren't shutting 
the car down quickly after the turbos have been exercising, that there 
should not be any problems.  I was hoping to lower the temperature 
threshold of the after run system to promote longevity rather than 
explore a "turbo timer" as this list knows it.  To date, I have done 
nothing to modify my 01 Avant, and don't really have any plans to do so 
unless it will add to the durability of the car.