Public Service Announcement: Change Your Soft-top Fluid - Mercedes-Benz Forum
 
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post #1 of 7 (permalink) Old 07-11-2019, 05:18 AM Thread Starter
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Public Service Announcement: Change Your Soft-top Fluid

So had a blissful weekend of auto repair as all my immediate family members went on their own vacations with friends and I got to stay home by myself.

In addition to fuel filter and CPS (which solved my occasional hard start and stalling issue) - I flushed my soft-top fluid. When I first bought the car, I did an exchange of some of the liquid with a turkey baster and refill, but that was 3 years ago. So this time I took off the return line and ran it into an empty OJ container, cycled the roll bar and soft-top a handful of times until it was fresh fluid flushing out.

Prior to the fluid refresh, my top opening process would pause after the rear of the soft-top was vertical and before the hatch opened. I'd have to give just a quick flick of the switch (not even let go completely, just a half-move forward and then back) and the process would complete. With the new juice, the process starts and finishes as it should.

This is what came out of the pump, and how it looked after. I'm guessing if you haven't thought about this for a while, you probably should. Easy enough to do annually.
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post #2 of 7 (permalink) Old 07-11-2019, 06:54 AM
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I personally think changing the hydraulic oil is unnecessary and of no benefit. But this is an area where I have no expertise, and my opinion should be discounted accordingly.
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post #3 of 7 (permalink) Old 07-11-2019, 07:10 AM Thread Starter
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Originally Posted by bobterry99 View Post
I personally think changing the hydraulic oil is unnecessary and of no benefit. But this is an area where I have no expertise, and my opinion should be discounted accordingly.
your opinion is valued - and I would agree that changing the fluid may be inessential in many/most cases. In my specific instance, evidence suggests that a pause in the soft-top opening sequence was eliminated between the period of having old fluid in the system and replacing it with new - with no intervention with SDS.
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post #4 of 7 (permalink) Old 07-11-2019, 08:25 AM
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Changing the fluid is always best. It breaks down over years. Same with replacing brake fluid, transmission, engine oil.
Which is the return line you disconnected?

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post #5 of 7 (permalink) Old 07-12-2019, 03:28 AM Thread Starter
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Which is the return line you disconnected?
The one closest to you as you stand looking into the trunk. The one just above that yellow screw. 11mm wrench. I was by myself, so I took out as much fluid as I could with the turkey baster and refilled. Capped the reservoir, and then started the car and cycled the rollbar a few times. Topped off the fluid. Then did the same with the soft-top. Putting the top up or down once pushed out most of the fluid but did not run it dry. So after about 5 (2 up, 3 down maybe) cycles, fluid was clear as you see in the photo.

Mine had been doing that quick pause thing since I had Top Hydraulics put new seals in all 11 of my cylinders (about 3 years ago). I never knew if it was like that before, or even if that was just how MB programmed it - because I bought the car in November with the hardtop on and top cylinders were one of the first repairs I did.

I use my top every chance I get - and the flush was easy enough to do, I could see ordering up a bottle of fluid when I need to get other parts and refreshing every spring. Probably overkill, but keeps me busy and out of trouble.
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post #6 of 7 (permalink) Old 07-13-2019, 12:09 AM
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I'm not sure if this is anything to go by, but my (recently sold) W124 wagon uses the same hydraulic oil for self-leveling rear suspension. Oil has never been changed and system worked for 32 years.

That said, if the fluid in R129 top pump reservoir looks filthy… common sense would suggest… replace it. Cheap and easy enough to do this without debating why and why not.

I replaced mine (via full flush) after cylinders were re-sealed. Once a year is certainly an overkill but… if it makes you happy.
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post #7 of 7 (permalink) Old 07-13-2019, 02:15 AM
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This oil is not like brake fluid and it does not absorb water or break down - the reason it goes black is because of all the seals wearing out.

Don't be surprised to see your cylinders start leaking in the months ahead. But sure there is no harm in changing it but only use the Mercedes fluid.
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