Re: Hydraulic fluid alternatives?

[Robert Myers <rmyers@inetone.net>]

Hi Y'all,

Two reposts from Ted Kublin <kublitv@msfcmail.msfc.nasa.gov>, with
permission.  

Good response, Ted.  Thanks.  Notice the address.  msfc = Marshall Space
Flight Center.  Seals?  Hmmmm.  Maybe....  :-)

Ted has quite a bit more expertise on oil seals than I do.  That's for
sure.  I can tell about the oil composition but the effects they have on
seals is not totally known to me.

________________________________________________________________

Hi Bob,

I read your post with some interest ...since I've owned Audi 5000/100
series cars with the pentosin fluids ....

IMHO, the main problem is finding a fluid that provides the proper amount
of seal swell - all the elastomeric seals in the steering rack & pump are
designed to swell by a controlled amount to provide a tight fit.  The
reason why ATF and other fluids cause leaks is NOT that they attack the
seals; it's that they provide insufficient swelling (or too much swelling)
of these seals.  Most of these mineral based oils are relatively benign and
are not going to degrade an elastomeric material that quickly - this would
evidence itself by leakage after a period of weeks or even months after the
changeover.

In case you were wondering about my address, I work as a propulsion
engineer for NASA in Huntsville, Alabama ...my specialty area is advanced
materials.  I also sell synthetic lubricants on the side, so I'm fairly
well versed in this area -

Sincerely,

Ted Kublin
___________________________________________

I replied to Ted and betrayed my lack of understanding.  So...

________________________________________________________________
Bob,

The point I was trying to make is that if you see leakage right away - say
within a week after putting the new fluid in there - it is probably due to
failure to match the seal swell characteristics of the original fluid.  In
some instances when the system has never been serviced, it's also possible
that the seals are varnished over and when the detergent additives in the
new fluid remove these deposits you get leakage through the dry,hardened
seals.  This is very common when switching neglected, high mileage,
engines/transmissions over to synthetic lubes.  An Audi technical made a
similar comment to me with regards to replacing brake fluid ....

Ted

__________________________________________________


___
   Bob
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