[urq] Re: Water Cooled Turbos - should be water jacketed turbos

[QSHIPQ at aol.com]

In a message dated 2/14/01 12:54:45 PM Central Standard Time, 
erickson at teleport.com writes:

Ned Ritchie quote:
>  NR> About 4 years ago I was embarrassed when talking to some
>  NR> folks who work building our Audi turbos at KKK.  I made
>  NR> mention of the oiled cooled turbos on the ur quattro.
>  NR> 
>  NR> Their response was,  "ALL our turbos are LUBRICATED by oil.
>  NR> Some are air cooled and some are water cooled."
>  NR> 
>  NR> I had to readjust my thinking.  Now when I order turbos
>  NR> they are specified as either water cooled or air cooled.
>  NR> 
>  NR> Ned Ritchie
>  
>  Not trying to bust you here; it just didn't jive with a memory fragment
>  floating around in my poor abused noggin.

BUST away!  Memory fragments in my head have been known to get lodged and 
mutated quite frequently.  The comment to Ned from kkk would really depend on 
which generation of NWJ turbo.  Here's why I say that, and this should make 
Ned feel a bit better:

SAE880258
Design Changes and Their effects on Deposits
"Following early failures turbocharger manufacturers have made several design 
changes mainly to the turbocharger center housing in attempts to overcome the 
heat soak problem before finally going to the water coooled designs.  In 
early designs there was no oil spray *cooling* and a very short heat path 
from the face of the casing adjacent to the hot turbine to the critical 
turbine bearing and the oil holes that feed it with oil.  
  In the next design stage the heat path was similar but the oil gallery was 
shortened. An oil spray hole was drilled, concentric with the oil gallery, to 
spray oil onto the hot casing wall to *cool* this area.  In the final 
*non-water cooled* version, the heat path from the hot area to the turbine 
bearing bush has been considerably increased and the oil spray hole has been 
re-directed to spray onto the rotating shaft to *cool* the hot wall by heat 
conduction and reduce heat transfer down the shaft to the bearing. " 

So, Ned's question was legitimate and properly phrased, the 'response' taken 
in current (at the time) manufacturing design.  Now he can feel vindicated, 
and I challenge the arrest ;).

That said, the comment would indicate that the procedure of "coasting" vs 
idling really has little merit in the context of water vs air/oil/convection. 
 Let the car idle before shutdown, the longer the better.  When I had my old 
GLH turbo, the boys in the engineering department indicated that 2 fan cycles 
was a good guildline (since the heat is drawn into the engine and coolant 
system rather quickly, the off mode is key to knowing that the turbo is in 
the cool down phase).

>  
>  FWIW, I do agree that the afterrun pump is not necessary with a proper
>  cool down.  I've been running my '89 200q without an afterrun pump for
>  six months prior to tearing down the head and swapping the
>  turbocharger.  (When it started leaking prodigiously on my honeymoon, it
>  got bypassed with a deepwell socket clamped into the hoses in it's
>  place.)
>  
>  I've seen no change in cool down characteristics in that time, nor did I
>  see any signs of oil coking in the turbo or feed/drain lines when I
>  removed them.  This may be due to the fact that I've run Mobil-1 since I
>  bought the car 60K ago.

A good synthetic is key.  The only way you really would see signs of coking 
is if you ran a chipped car really hot, then shut it off.  But even then the 
coolant tends to vaporize before coke buildup would occur

>  
>  Which may be a sign that afterrun pumps may have been a necessary evil
>  in the days pre-synthetic oils, but may be successfully ignored today
>  with the careful choice of lubricants during routine maintenance.

Agreed, not really sure why we still see it, but warrantee claims on audi 
turbos has always seemed rather high to me vs the norm.  Darn those 
tweeksters 

HTH
;)

SJ