Pentosin, Oh Pentosin! (long)

[Phil Rose <pjrose@servtech.com>]

I sure would like to better understand the Pentosin "issue". I have no
intention of using ATF, but what about Pentosin 7.1 vs 11S??? I suppose
it's old hat to most of you, so I'm sorry for the WOB in retracing the
trail of green tears.

My '91 200q bears the inevitable label ("use G002 000 mineral oil only") on
the reservoir. It contains hydraulic fluid that appears only very _faintly_
yellowish when viewed in a pipette tube (OK maybe a slight greenish tinge,
if a lot of imagination is used). That's also the color my local Audi parts
guy describes for the sanctified G002 000 fluid they presently dispense. Is
this different than the color of "green" Pentosin 7.1??? I suppose it's
possible that when a much thicker (larger) layer of my car's PS fluid is
viewed, it may merit the unequivocal "green" designation that people on the
qlist apply to Pentosin 7.1. But....anyway, I wonder which fluid  was put
in my car at the factory in late 1990? And what type of fluid was added to
it at later dates?

Results of several recent phone calls---->

(1) AoA Customer Service claims there is only one fluid p/n ever specified
for use in Audi PS pumps, and they conveniently identify that only as G002
000. My understanding is that at one time, G002 000 actually meant
"Pentosin 7.1".

(2) Customer Service claims to have no info available on G002 000
composition (or when it may have changed), but I got the dealer parts dept.
guy to read the label on a can of their G002 000, and the following words
of comfort appear:

 "contains Pentosin 11S" !!!!

[Not to confuse the issue, but Audi also use a p/n G002 012 fluid, which
they claim is merely a 12 oz quantity of the same G002 000.]

So, as we all knew, Audi at some time in the not-so-distant past changed
their hydr. fluid from Pentosin 7.1 (mineral oil) to Pentosin 11S (a
synthetic blend containing mineral oil), but they retained the same p/n.
But starting with what model year? And should anyone care? Some say "Yes!",
while others think it probably matters not at all.

Not matter? But, but, but there's that ominous warning on our non-OEM
Pentosin 11S labels that it "must *not* be mixed with mineral oil or any
other hydraulic fluids". Right? Yet it is clear that Audi is doing exactly
that--considering all the older Pentosin 7.1-containing cars that they
service. Therefore, either Audi is inflicting significant harm to
customers' hydraulic systems (class action suit?), or in fact, there's
really *no harm* done by mixing the two flavors of Pentosin. I'd like to
believe the latter is true, although the high frequency of PS seal leakage
raises the suspicion that admixture of 11S and 7.1 fluids might indeed be
unhealthy. Bet you won't get Audi to admit that...:(

Assuming Audi is not criminally negligent, it must be that Pentosin 11S is
indeed  _backward_ compatible with 7.1 (i.e., that it's OK to replace 7.1
by 11S). But what about that warning, you ask? Well, I don't know. Possibly
it just doesn't apply to Audi components, or it might indicate that the
reverse, i.e., replacing 11S by 7.1, is not advisable. Thus, if 11S tended
to swell rubber seals, then it might not cause seal problems (leakage) when
added to a Pentosin 7.1 system--if the latter is a relatively non-swelling
fluid. But if admixture occured in the opposite sense (7.1 added to an
established 11S system) some _de_swelling of seals might start to occur and
eventually...leakage. Pardon the hand-waving, but it's all I can think of
at the moment. Whether this reasoning would be applicable to steering rack
issues, I don't have a clue.

Based on my present level of ignorance, when I rebuild my PS pump (if
Carlsen ever gets the kit shipped to me :( ) I'm probably going to flush
and refill with Pentosin 11S. And keep my fingers crossed...

Phil R.

P.S. If anyone wonders, there's a simple explanation as to why swollen
seals will often begin to leak after they've been de-swollen--even though
the same seals can seal OK if never swollen to begin with. A similar
phenomenon occurs in woodworking joints, too.




Phil Rose				Rochester, NY
'89 100 (For Sale, 111K, automatic)
'91 200q				mailto:pjrose@servtech.com