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  #1  
Old 05-11-2012, 10:47 AM
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Mixing ATF and Power Steering Fluid in Steering System

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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  #2  
Old 05-11-2012, 11:51 AM
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Quote:
Originally Posted by shertex View Post

My question: is there any problem with mixing the two fluids?
No.
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  #3  
Old 05-11-2012, 11:56 AM
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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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  #4  
Old 05-11-2012, 12:26 PM
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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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  #5  
Old 05-11-2012, 01:14 PM
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Quote:
Originally Posted by shertex View Post
.I'm just not interested in completely flushing the system.
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.
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  #6  
Old 05-11-2012, 01:19 PM
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I know the procedure....no thanks...but to each his own.

Quote:
Originally Posted by Brian Carlton View Post
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.
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06 E320 CDI "Rutherford", Black on Tan, 171k mi, Stage 1 tune, tuned TCU
91 300D "Otis", Smoke Silver, 142k mi, wastegate conversion

19 Honda CR-V EX 61k mi
Fourteen other MB's owned and sold
1961 Very Tolerant Wife
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  #7  
Old 05-11-2012, 01:21 PM
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Quote:
Originally Posted by shertex View Post
I know the procedure....no thanks...but to each his own.
Then just stay with the ATF..........it's clean and it works fine..........
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  #8  
Old 05-11-2012, 02:52 PM
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Quote:
Originally Posted by Brian Carlton View Post
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.
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14 E250 Bluetec "Sinclair", Palladium Silver on Black, 153k miles
06 E320 CDI "Rutherford", Black on Tan, 171k mi, Stage 1 tune, tuned TCU
91 300D "Otis", Smoke Silver, 142k mi, wastegate conversion

19 Honda CR-V EX 61k mi
Fourteen other MB's owned and sold
1961 Very Tolerant Wife
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  #9  
Old 05-11-2012, 02:57 PM
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Quote:
Originally Posted by shertex View Post
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.
Are you going to avoid using ATF in your transmission as well?
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  #10  
Old 05-11-2012, 02:58 PM
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Quote:
Originally Posted by shertex View Post
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.
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.
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  #11  
Old 05-11-2012, 03:00 PM
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Quote:
Originally Posted by tangofox007 View Post
Are you going to avoid using ATF in your transmission as well?
Uh....no. I'm not sure the question makes sense. No one has ever claimed that modern ATF forumations compromise tranny seals. But if your point is that a seal is a seal is a seal, then I guess I see your point.
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06 E320 CDI "Rutherford", Black on Tan, 171k mi, Stage 1 tune, tuned TCU
91 300D "Otis", Smoke Silver, 142k mi, wastegate conversion

19 Honda CR-V EX 61k mi
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1961 Very Tolerant Wife
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  #12  
Old 05-11-2012, 03:36 PM
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Quote:
Originally Posted by shertex View Post
No one has ever claimed that modern ATF forumations compromise tranny seals.
Who claims that "modern" ATF "compromises" power steering seals? Aside from individuals repeating rumors, that is. Do you have reliable data that says that the owner's manual information should be disregarded?

Here are the relevant facts as I see them:
1. MB has never revised its power steering fluid recommendation for vehicles that originally used ATF in the PS systems.
2. The owner of the Dexron brand (GM) has specified each follow-on Dexron formulation is fully backwards compatible.
3. MB isn't exactly uninvolved when it comes to acceptable fluids. http://bevo.mercedes-benz.com/bevolisten/bevo-sheets-sort1.html
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  #13  
Old 05-11-2012, 03:45 PM
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I do wonder when MB switched their recommendation, and why. On my 91, they specify power steering fluid. I assume that the 86 specifies ATF, but I don't have a manual so I'm not sure.
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14 E250 Bluetec "Sinclair", Palladium Silver on Black, 153k miles
06 E320 CDI "Rutherford", Black on Tan, 171k mi, Stage 1 tune, tuned TCU
91 300D "Otis", Smoke Silver, 142k mi, wastegate conversion

19 Honda CR-V EX 61k mi
Fourteen other MB's owned and sold
1961 Very Tolerant Wife
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  #14  
Old 05-11-2012, 04:25 PM
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I think mercedes switched the recommended fluid when they went to the one serpentine belt in the very late 80's. I have been using ATF in my 240D for 30 years with no issues.
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  #15  
Old 05-11-2012, 05:21 PM
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Fluid dynamics

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

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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
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