1999 S70 steering rack, 2004-2012 S40 electric steering pump. Which hydraulic fluid to use?

[ThaddeusTheBold]

Hi,

I am converting my 1999 Volvo S70 T5 to full electric. The engine is out. Now stuff is finally going in.

One of the things I have to put in is an electric steering pump. I got one off eBay, a Volvo unit from a 2004-2012 S40/V50/C30.

The manual in my S70 said to use ATF in the original power steering system. The online references I see for the electric power steering pump seem to call for Pentosin.

Detective work: The fluid that's left over in the steering rack seems to be neither. To be honest, it looks like motor oil. I wouldn't put it past the prior owner to have dumped regular oil in there out of laziness, cheapness, or ignorance. I am praying it's not the case though, maybe it's some sort of synthetic ATF. I can't tell what was originally in the PS pump. It's grey, TBH. But I think that, held up under just the right intense light, it may have a green tint: Pentosin.

Here's my dilemma: which fluid should I use? Assuming the rack used ATF, and the pump used Pentosin, which should I use now? Will Pentosin hurt the rack? Will ATF hurt the pump?

Help me, oh my Volvo brethren. I need the best compromise, for reliable function: ATF or Pentosin.

Thanks!

[abscate]

As we say in mathematics , the first problem will be to establish the existence of a compatible fluid between the electric pump and the hydraulic rack

After that is known, uniqueness will hopefully not be a problem.

[ThaddeusTheBold]

Well, I'm going to go with the Pentosin. Here's why:

Pentosin is spec'd for some V70's of the same year. V70's appear to use the same PS rack as the S70. So it's possible the rack in my car is fine wih the stuff.

I also thought about failure modes. Pentosin is thinner than ATF. If the pump likes Pentosin, it might damage it to put a heavier fluid in there and expect it to pump. The thinner Pentosin MIGHT sneak past the seals on the ps rack, but again it might not. In the parade of horribles, a leaky PS rack (which may need replacement soon anyway) seems like a less horrific issue than a PS pump that seizes up.

I'll resurrect this thread as needed to let y'all know how it turned out.

[V50M66]

Pentosin CHF11S (and later CHF202, which are compatible with each other) is the recommended fluid for all '99 and up Volvos. The fluid is dictated by the pump, not the rack

[Shift727]

Did you ever finish this project? Is the powersteering electric now?