Re: ATF in a hydraulic oil car. BTDT?

[Jeff Mruss <rmruss@pangea.ca>]

I can't comment on the later pumps, but the PO of my '84 5KS (Dad) was using ATF in the hydraulic system for at least 10 years, and the pump did not leak.  In fact, the pump only failed shortly after I replaced the leaking rack and changed back to Pentosin, and it still wasn't leaking, just no pressure.

I've never really given this much thought before, since the list consensus is that ATF/PS fluid is bad in Pentosin cars, but does the theory that ATF/PS fluid "rots the seals" make any sense?  I did the pump rebuild, and the EXTREMELY expensive O rings I used didn't look like they were made of special rubber, they just looked like O rings.  Perhaps I'm completely off base here, but doesn't the reason ATF/PS fluid shouldn't be used in a Pentosin car probably have to do with the differing viscosities of the fluids, rather than any seal rotting properties?  I'd bet that the vast majority of cars where ATF/PS "rotted the seals" were already leaking when the extra fluid was added, otherwise, why would you need to add fluid?  

There must be people on this list who have had the seals on their pump go bad even though they were using Pentosin.  After my pump rebuild attempt was unsuccessful (bad pressure relief valve I think) I installed several used pumps.  The first two pumps leaked from the front seals, and both of them arrived with a bit of Pentosin still left in them, so I don't think the wrong fluid was the problem.

Preparing for the e-mail avalanche,

Jeff Mruss