I've read various threads in the past as to people's reasons for using either ATF or power steering fluid in the power steering system. We all know that, in some of our cars, it is ATF that's recommended in the manual. But, ATF formulations changed. So a lot of us just use generic power steering fluid....whatever's cheap at Walmart.

My question: is there any problem with mixing the two fluids? If so, why?

My method of renewing the fluid is simply to drain and fill the reservoir periodically....I'm just not interested in completely flushing the system. So, with the SDL I just acquired (PO used ATF) I was just going to start fluid renewals using power steering fluid.

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14 E250 Bluetec 4Matic "Sinclair", Palladium Silver on Black, 158k miles
06 E320 CDI "Rutherford", Black on Tan, 177k mi, Stage 1 tune, tuned TCU
91 300D "Otis", Smoke Silver on Tan, 144k mi, wastegate conversion, ALDA delete

19 Honda CR-V EX 72k mi
Fourteen other MB's owned and sold
1961 Very Tolerant Wife

No.

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When cryptography is outlawed, bayl bhgynjf jvyy unir cevinpl.

I run Dex3 or Prestone Power Steering with "seal re-juvenator" (stop leak that doesn't work by being stupid thick) and I've occasionally used real MB PS fluid. Never had any issues.

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68 280SL - 70 280SL - 70 300SEL 3.5 - 72 350SL - 72 280SEL 4.5 - 72 220 - 72 220D - 73 450SL - 84 230GE - 87 200TD - 90 190E 2.0 - 03 G500

Nissan GTR - Nissan Skyline GTS25T - Toyota GTFour - Rover Mini - Toyota Land Cruiser HJ60 - Cadillac Eldorado - BMW E30 - BMW 135i

Since many MBs go to the junkyard without ever having their PS fluid changed (Mercedes mentions only "checking" the fluid in their service manuals), anything you do has gotta be better than what happens to other cars. If you have concerns, try mixing a little of the two fluids in a glass dish and see what happens.

I've used both the "flush" and the "reservoir change" method. Both work.

Jeremy

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"Buster" in the '95

Our all-Diesel family
1996 E300D (W210) . .338,000 miles Wife's car
2005 E320 CDI . . 113,000 miles My car
Santa Rosa population 176,762 (2022)
Total. . . . . . . . . . . . 627,762
"Oh lord won't you buy me a Mercedes Benz."
-- Janis Joplin, October 1, 1970

Don't be so GD lazy.

Disconnect the return hose from the pump and place it in a pail.

Get another person to sit behind the wheel.

Get one gallon of PS fluid.

Open cap on pump.

Start engine and ask other person to turn wheel from left to right (and repeat several times).

Pour fluid as fast as necessary to prevent reservoir from going dry.

Stop engine after about three quarts have been dumped.

Reconnect return hose.

Fill reservoir to required level.

Install cap.

Toss out old transmission fluid (or burn it in the tank).

Done.


I'm still unsure of why you want to switch it to PS fluid? If the switch was made prior to the pump seals leaking, you might have an argument. But, the pump seals need to be done in any case. The current ATF is pristine clean due to the leak.



FWIW, I do not believe anyone can state, for certainty, that the two fluids are definitely compatible with each other over a long time interval. Personally, I would not mix them.

I know the procedure....no thanks...but to each his own.

__________________
14 E250 Bluetec 4Matic "Sinclair", Palladium Silver on Black, 158k miles
06 E320 CDI "Rutherford", Black on Tan, 177k mi, Stage 1 tune, tuned TCU
91 300D "Otis", Smoke Silver on Tan, 144k mi, wastegate conversion, ALDA delete

19 Honda CR-V EX 72k mi
Fourteen other MB's owned and sold
1961 Very Tolerant Wife

Then just stay with the ATF..........it's clean and it works fine..........

Perhaps....but I'm not convinced ATF is fine. I'm sure you've read the threads over the years. Although ATF is specified in the manual, the argument of some is that the formula is sufficiently different these days that it can compromise the seals. While I doubt anyone can know for sure one way or the other, that's why I've always avoided using ATF in the steering systems.

__________________
14 E250 Bluetec 4Matic "Sinclair", Palladium Silver on Black, 158k miles
06 E320 CDI "Rutherford", Black on Tan, 177k mi, Stage 1 tune, tuned TCU
91 300D "Otis", Smoke Silver on Tan, 144k mi, wastegate conversion, ALDA delete

19 Honda CR-V EX 72k mi
Fourteen other MB's owned and sold
1961 Very Tolerant Wife

Are you going to avoid using ATF in your transmission as well?

__________________
When cryptography is outlawed, bayl bhgynjf jvyy unir cevinpl.

The point is..........the seals are already compromised..........and you're going to change the seals.

With brand new seals, the point is moot. The ATF won't compromise the new seals for quite a long time...........if at all.

And, if you mix ATF with PS fluid, you haven't avoided that compromise of seals if it does exist.

I would like to use Brian's method (and I have used it) but currently have two concerns:
(1) With the engine idling, fluid goes through so fast that it's almost impossible to keep the reservoir filled. I've though of clamping the return hose so that the fluid flow is reduced but that would create higher pressures in the system and I don't want to blow a seal somewhere.
(2) Some cars, like my '95 E300D, so carefully hide the return hose under the intake manifold that it pretty much requires pulling the manifold. This I don't want to do just to change fluid.

As to ATF vs. PS fluid, I suspect that the two are sufficiently similar that it's a moot point. When I drove GM iron, I used ATF in the PS circuit and never had a problem. OTOH, I use PS fluid in my Benzes because two of them have weak pumps (200,000 miles without ever changing the fluid didn't help) and I want to give them every chance I can to last a few more miles.

PS fluid isn't expensive so there's really not much reason not to use it unless ATF is all that's available in your particular situation. The important thing is to get the dirty fluid out and replaced by clean fluid that bears some family resemblance to PS fluid. One thing I have noticed is that it's easier to tell when the PS fluid is getting dirty if you use a colorless fluid (most ATFs are red). You may have to pop a few bottle caps to find a colorless PS fluid but they're out there.

Jeremy

__________________

"Buster" in the '95

Our all-Diesel family
1996 E300D (W210) . .338,000 miles Wife's car
2005 E320 CDI . . 113,000 miles My car
Santa Rosa population 176,762 (2022)
Total. . . . . . . . . . . . 627,762
"Oh lord won't you buy me a Mercedes Benz."
-- Janis Joplin, October 1, 1970