[s-cars] Oil and Turbos

[Scott Justusson]

It seems no surprise to me, and the advantage Chrysler found in
designing the WC center bearing sections.  I spoke to one of the lead
engineers at Chrysler when the whole WC center bearing design was
introduced back in 1984.  As he explained it to me, you only need to
make enough water circulate thru the system at 15psi, so that a 1600F
bearing housing doesn't vaporize the coolant.  IIRC, in the Audi kkk,
they document something north of 6.5 liters a minute.  WRT coking
present, it's easy to see it at the oil lines, how do you see it at a
piston ring?  I've seen many failures of Audi piston rings that I
attributed to coking causing them to be extremely brittle.  Remember, if
you hose those piston skirts with hot oil, they aren't doing much to
cool pistons and rings.
 
Coking is really a shutdown problem, not a running problem - the SAE
"Severe Turbocharger Bench Test" Paper shows that even on extreme heat
cycling the highest coking risk is a shutdown problem.  Even with WC
center bearings, a good idea to take 2-3 minutes to allow the turbo to
cool while the engine is running.  Chrysler actually had this
instruction in the owners manual of the GLH turbo (no afterrun pump).  
 
I agree with an after-run pump being bypassed, it's a bad idea.  But, I
also think that the after-run circuit in the 5kt and 200t was much more
frequent (like for 5 minutes after every run cycle = pump and low speed
fan) than the S car, which IME, properly functioning rarely turns on in
comparison.
 
WRT comments on oil temps, the SAE tests used in attaining these temps
were pretty extreme, more so than any normal drive cycle.  Remember,
they were evaluating turbo and oil failure, not just observing temps.
Manny, my summary would be this:  Your observed oil temps are too high,
and you should expect engine failure to be the result.  Put in an
aftermarket oil cooler (Summit Racing carries Earls), I found even the
19row is better than a stocker, and if you are routinely
tracking/altitude, a 36 row will make the oil temps a non issue.   With
FMIC applications, the best spot is where the stock IC used to be.  You
will find the 20feet of line to get there and back to be more expensive
than the oil cooler itself, btpt.
 
HTH and my  .02
 
Scott J
 
-----Original Message-----
From: djdawson2 at aol.com [mailto:djdawson2 at aol.com] 
Sent: Tuesday, March 24, 2009 10:15 PM
To: qshipq at aol.com; trgreen at comcast.net
Cc: manuelsanchez at starpower.net; s-car-list at audifans.com
Subject: Re: Oil and Turbos
 
Interesting info...

It seems almost hard to believe that you can get the hot side of a turbo
glowing red, yet the bearing temp only sees 120C.

It still seems to me that the turbo is where oil failure is most likely
to occur, just based on years of history looking at coked/plugged oil
return lines.  I don't dispute the facts you've presented, it just seems
to be a more frequent point of failure... one way or the other.

It's tough to read chat on the list about substituting an elbow in place
of the after-run pump... bad choice of solution for anything other than
getting home. 
 
 
-----Original Message-----
From: Scott Justusson <qshipq at aol.com>
To: 'Tom Green' <trgreen at comcast.net>; djdawson2 at aol.com
Cc: manuelsanchez at starpower.net; s-car-list at audifans.com
Sent: Tue, 24 Mar 2009 8:44 pm
Subject: RE: Oil and Turbos







Audi wrote the book on all this turbo/oil stuff, specifically






co/authored many SAE papers on the subject, before and after watercooled






turbos/synthetic oils. Specific to this topic ---  See 880258 "The






development of a Severe Turbocharger Bench Engine Test" and 860103 "The






third-Generation Turbocharged Engine for the Audi
 5000 CS and 5000CS






Quattro", and 970922 "Development of Modern Engine Lubrication Systems".




















Relevant Info to this thread:













860103 - Running I5 turbo motor, the temps of the piston ring with






watercooling are 190C, temps of the turbo bearing housing 120C.






Shutdown kills engines if the water circulation circuit is not






functioning.  Without water cooling the numbers are 260C PR and 140C






TBH.  On shut down, the non water cooled temps go to 360C PR and 250TBH






within 2 minutes of heat soak.  













Rule:  Make sure your after run pump is working.  Regardless, some






idling before shutdown never hurts.