[BiturboS4] After run pump - Todd are you here?

j y jimnetpa at yahoo.com
Thu Jul 10 19:42:03 EDT 2003

[ Picked text/plain from multipart/alternative ]
Thanks for the 411 (info). I found it interesting. My Porsche 951 is a 1986. Your points make sense because the guys on the 951 board @ Rennlist are always worried about 'coking'.

cwurts12 <cwurts12 at mindspring.com> wrote:
On Thursday, July 10, 2003, at 12:00 PM, biturbos4-request at audifans.com

> Yes, I am familair with the "after-run pump" because I also own a
> Porsche 9=
> 51 (944 turbo) and the "after-run pump" operation is very evident
> (from the=
> fan noise).
> I did not experience this after-run fan noise with my S4 prior to
> blowing a=
> turbo and having them replaced by AoA. Since AoA replaced the
> originals tu=
> rbos with upgraded K03s the fan noise from the after-run pump is VERY
> evide=
> nt.
> Personally, I don't believe that the temperature setting for the
> after-run =
> pump was set correctly when my car originally left the factory. Again,
> the =
> fan noise from my S4 after-run pump is very evident now (just like my
> Porsc=
> he) where it was non-existent (IMO) be4.
> Stays on VERY long after hard runs and is VERY loud (can hear it from
> insid=
> e my house (windows open) when the car is parked at the curb outside -
> just=
> like my Porsche).
> jy

I find this to be an interesting subject as well. In my previous
experience with several 5ktqs and a UrS6, the after run pump and fan
would run after almost any normal driving other than winter. I always
found this to be very comforting. I tried very hard (with me ears) to
detect any evidence of after run activity, but never could, even on the
hottest of days. I dropped by AWE one day and asked Todd about this
question. I also asked if I could change a tstat to bring the after
run pump on at lower temps. His response was interesting, and I invite
him to chime in if he is here.

He said the issues surrounding the old days of after run pumps were
different 10 years ago. The concern then was primarily coking, where
today he said the the issue surrounds metallurgy. If I understand this
correctly, the temps that coking occurs is much higher today (because
of chemistry and synthetics) and the after run tstat is set higher than
it used to be, and is higher than the normal operating temp of the
engine. So apparently coking isn't as big a concern. Now the concerns
are with regard to the metal shaft through the center of the turbo;
when very hot it can sag and cool out of round leading to failure. So
the best line of defense is to leave the engine idling long enough for
the spindle to cool.

I wonder if Audi has made the change to the after run tstat? This
would be valuable information for all of us.

01 S4 Avant
90 V8

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