[urq] Water Cooled Turbos

[QSHIPQ at aol.com]

To be honest Kevin, I don't think *experience* has much to do with the 
problem here.  I have no doubt that Phil could have shared his 'experience' 
wrt piston rings, and not "seen any problems" with rings (whatever that 
means).  Rings are funny things, they are either intact or they're not.  As a 
rather anal guy about motor rebuilds, I'd never tear a motor down and not 
replace the rings anyway, being right there is tough to ignore (I have a 
great hope that this is Phil's modus as well).  That said, I kinda smile some 
at teardown "inspections".  Really what gives the indication of pison ring 
damage, is *before* teardown, with a leakdown test.  After teardown, a really 
brittle ring will shatter, one that's not so won't now, but is it better or 
the same as new?  Is heat cycling and it's range a major component of 
premature piston ring failure?  You bet.

The bottom line here is that, regardless of 'experience', an oil cooled turbo 
puts massive heat stresses on the piston rings, during hot runs AND shutdown. 
 Heat cycling metal components causes stress, the higher the heat, the more 
the stress, which leads to failure.  Remember too that oil carbonization 
occurs as well, and that carbon attaches itself to the really hot components, 
turbo bearings, turbo journals, and piston rings.  This causes further stress 
on the components.  A good synthetic oil may decrease the failure rate 
observed, but it really hasn't addressd the inherent problems with oil cooled 
turbos.  

So here, I kinda discount any *experience* regarding piston ring failure, 
only point to the data regarding the temps.  Peak piston ring temps is less 
than 1/2 comparing oil cooled with water cooled turbocharger units, in a 
paper published by audi AG.  Any further SAE research would indicate, audi 
isn't alone in this conclusion.  

I'm all for doing things right based on sound theory and practice.  Here, the 
evolution of the turbocharger would definitively indicate that a watercooled 
turbocharger upgrade to an oil cooled application, has nothing but win-win 
associated with it, in terms of heat and performance.  And further win-win, 
it's an upgrade that can be done with stock audi parts off used WC turbo 
audis, or ordered new from your local dealer.  

All that said, I'm an idiot that just works on 'em, drives em hard, and likes 
to read some of the experiences on these lists.  I'm no longer surprised that 
there aren't true audi experts posting here.  Misinformation and incorrect 
theory and application are tough ways to guild those not so acute to their 
audis.  These audi lists should be a resource of information and btdt.  That 
said Phil's anecdotal experience with engine teardowns, really has nothing to 
do with the inherent flaws of oil cooled turbos in theory or application.  
Presenting personal anecdotes as 'expert' testimony contradicting known 
theory and app, doesn't make any sense to me.  And this isn't the first time.

Go figure.

Scott Justusson
'83 urq w/c k26



 




In a message dated 2/15/01 7:16:11 PM Central Standard Time, 
kevphill at mediaone.net writes:

> Having moved from right to left over the pond I have a theory as to why my 2
>  learned friends have different experience with this problem.
>  
>  England never experiences the extreme temperatures that the USA does for
>  extended periods of time during the summer + AC was not fitted as standard
>  to the urq. It gets bloody hot and humid over here and that will raise 
under
>  hood temperatures by a long way.
>  So is it the enviroment that the car is operating in that is causing the
>  damage that Scott has seen but Phil never has ???
>  
>  Kevin Phillips
>  Western Massachusetts
>  1990 200q
>  1995 900 SET
>  Cell 413 519 9034
>  
>