I've been mulling this over in my head for a while, and wondered what you guys would think about this subject.

I've read some comments that using modern ATF in the power steering system of our old Mercedes is not recommended, it doesn't play well with the seals. What about using a mineral oil? I'm stocked up on Pentosin CHF 7.1 and am pondering using this in my SDL's power steering. CHF 7.1 is very similar to (if not the same as?) the old mineral oil SLS fluid. My Audi uses this for the power steering and brake assist, and both of my Jetta ECOdiesels had this from the factory in the steering.

I've also got CHF 11S on hand. This is what virtually every modern German car used in their power steering systems. It's a very fancy synthetic fluid, and thus costs $10 more per liter then the old 7.1 fluid. I think I'll save my stockpile of 11S for my TDI

I've got generic clear "Power Steering" fluid in my SDL now, and am not 100% happy with its performance. It's possible to use up all of the pump's pressure doing quick wheel turns at low engine speeds. I don't recall the car doing this when I initially had it, but flushing out the old ATF in the system was one if the first things I did so I may not be remembering correctly.

-Jason

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1991 350SDL. 230,000 miles (new motor @ 150,000). Blown head gasket

Tesla Model 3. 205,000 miles. Been to 48 states!
Past: A fleet of VW TDIs.... including a V10,a Dieselgate Passat, and 2 ECOdiesels.
2014 Cadillac ELR
2013 Fiat 500E.

I may be dead wrong, but this makes me suspect a weak pump rather than a poor choice of fluid. The nature of hydraulics tends to be that you can put dang near anything you want to in there, and it'll either work or it won't. One of the old farm tractors we're running has power steering, and it leaks so fast it's not worth wasting good fluid on. When we really want it working, we've been known to put waste motor oil in there.

Yes, I know a Mercedes isn't a tractor. No, I wouldn't recommend waste oil in a new, working system. My point is, in most of the power steerings I've encountered (Mercedes included; done the ATF/PSF switch out a few times) it either works or it doesn't regardless of what you pour into it as long as it's working at all. I'd be inclined to suspect a weak pump IF this is a real symptom.

I've never noticed mine getting "overpowered" but then I don't know that I would. I just know I don't have trouble turning the car.

I know this is a basic question, but are you quite certain you have the reservoir full enough? One of mine has leaky hoses and I can tell that it's time to add fluid by the difficulty in turning the wheel as well as the whining/groaning sound that only comes from dry power steering pumps. I'm wondering if yours is only marginally full and if you turn the wheel fast enough, you momentarily drain the reservoir or something.

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~Michael S.~
Past cars:

1986 300SDL
1987 300SDL
1982 240D
1982 300SD


Current:

1987 300SDL

Fluid is at the correct level. Filter is new too. I'm probably just being overly picky. My car did get a new pump put on by the dealer at 50,000 miles, I wouldn't think it is worn out by 150k but I guess you never know.

Not that anyone would ever use bio for a power steering pump (in a car), but ----- I recently used a PS pump to power a centrifuge for cleaning biodiesel. Seals deformed after only a few hours of operation.

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John Schroader
bio burnin' 83 300D, '83 300 SD, '79 240D
"I've never met a man who was good at making excuses who was good at anything else" Ben Franklin
"You cannot permanently help a man by doing for him what he could and should do for himself" Abraham Lincoln