[s-cars] Oil and Turbos

[Scott Justusson]

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.

Manny, leakdown of </=10% is good, =/>20% is bad.  Do compression check
first.  IME, the 25 row oil cooler is a good match for the I5 20vt.  At
90+F track day running an S car hard with a 25 row cooler, I observed a
peak of 120C, and by the time we got to back into the pits the temp was
at or under 100C.  For a dedicated track car a 36 row is better, but
overkill (read tough to get up to 100C) for daily driving.  Altitude and
an FMIC, might be better with the 36 row, but that's a big dog to stuff
under the hood of the dog house.

Specific to the concerns on oil temps in other cars, the rule of thumb
is you want the oil temp to reach 100C to burn off the moisture in the
oil.  Since all Audi turbo cars come with 100C oil cooler thermostats
from the factory, this should be a non issue on the AAN.

HTH and my .02

Scott J


-----Original Message-----
From: s-car-list-bounces at audifans.com
[mailto:s-car-list-bounces at audifans.com] On Behalf Of Tom Green
Sent: Tuesday, March 24, 2009 7:15 PM
To: djdawson2 at aol.com
Cc: manuelsanchez at starpower.net; s-car-list at audifans.com
Subject: Re: [s-cars] Oil Temperature

I just know better than to touch any of this stuff when it's hot.    
But, I am sure that the oil temps are high enough to coke conventional
oil at 150ºC, and at that inlet temperature, it would be hotter in the  
turbo.  What was engineered to work just fine for 50K miles is
not necessarily just fine at 150K miles.  The advantages of synthetic  
are proven for the turbo applications, which is what I wanted to
convey.

I think Manny's OEM cooler can keep up with the RS2 if it is in good  
condition.  Most I see have coils almost filled with oily dirt on the
outside.  Insides can be nasty also, so I would check the present oil  
cooler out before opting to buy an aftermarket system.  Perhaps
he needs a bigger cooler.  I certainly don't want to suggest that  
Manny needs to "back off" on any of his sessions.  : > )

Tom

On Mar 24, 2009, at 6:44 PM, djdawson2 at aol.com wrote:

> I think the bearing section of the turbo is, without question, the  
> place where oil temps are highest... hence the after-cooling pump.
>
>
> -----Original Message-----
> From: Brett Dikeman <brett.dikeman at gmail.com>
> To: Tom Green <trgreen at comcast.net>
> Cc: Manuel Sanchez <manuelsanchez at starpower.net>; Scarlist
<s-car-list at audifans.com 
> >
> Sent: Tue, 24 Mar 2009 2:29 pm
> Subject: Re: [s-cars] Oil Temperature
>
> On Tue, Mar 24, 2009 at 3:36 PM, Tom Green <trgreen at comcast.net>  
> wrote:
>
>
>
> > At the turbo, the oil probably reaches the flash point, so that  
> can't be good.
>
>
>
> I'm not sure what the relevance of flash points are, but the flash
>
> point of 15w50 Mobil1 is 235C; 455F.  The coke point of most
>
> synthetics is even higher.  In a water-cooled-center-section k24, you
>
> think the oil is heated by a differential of more than 100C from the
>
> coolant?  These cars were designed to work just fine on dino oil...
>
>
>
> One would think oil sees the hottest surfaces around the
>
> pistons/rings/cylinder wall.
>
>
>
> Brett