Fluid Renewal Question
 

I'll pose this as a generic question:

From a fluid quality perspective, which is better and why (or does it not make a difference)?

Every 30k miles doing three drain and fills of ATF resulting in fluid that is 80% pure (i.e. new).

Every 10k miles doing one drain and fill of ATF resulting in fluid that is 42% pure.

Removing the torque converter drain plug is important to get most fluid out. I would never change tranny fluid every 30,000 mi. Most of my U.S. cars say it never needs changing (unless taxi or police service), though I change it when replacing the filter maybe every 200,000 mi. I doubt M-B trannys are wimpier. You could drive yourself bonkers trying to follow the M-B service requirements.

I've heard that the regular fluid changes are to protect the seals on the transmission. They're all pretty much a PITA to change. Besides, most new cars are built to last 200K miles while a diesel Mercedes is built to last forever. Another consideration is that the seals deteriorate with age more than mileage and you're probably not going to see many 2000 something cars on the road 30 years from now...

Dkr.

It would drive me bonkers if I didn't follow the manufacturer's recommendations. As far as I can tell, doing so has served me well.

My question is simply a generic question comparing two different approaches to fluid renewal....

If you remove the transmission pan more frequently. The chances of it leaking one time may grow. Not because the pan is distorted with proper bolt tightening though. Just average luck of the draw.

There are additives in transmission oil I suspect or certain charactaristics of the fluid may change somewhat over time and miles. So it is probably better to do periodic changes.

Todays transmission fluid may be superior enough or improved enough since these cars where produced to extend it a little as well. Best source of information in that regard may be the companies that manufacture the fluid. It takes little more effort really to do a more total change when you do one anyways.

Certainly if it is not a nice red color something is going on or it needs changed.

For the 722.6 trans the recommended interval is currently 60k Km IIRC. Filled for life disappeared a long time ago.

If you've priced the MB fluid, you probably wouldn't consider either 3 flush version, although there are now off the shelf fluids that meet spec.

Mine typically used 7.5L of fluid with the pan and TC drained overnight.

Not asking about any particular car....again, just a generic question.

As a degreed and licensed (just EIT, no PE here) mechanical engineer who spent a few years involved in automotive durability testing, I can say with confidence that I have no freaking idea. We never got into that. We always just followed the manufacturer's maintenance schedule for the duty cycle we were testing to and documented and corrected the failures on the test article as they occurred.

Since it is a generic question better than ninety percent of cars will not have a torque converter drain I suspect. So if a power flush change is available on a newer lower milage car it might be considered.

I have never had one done myself. Plus I seriously doubt I would have one done on an older automatic transmission.

Really though I think the partial change is well calculated with a new Filter installed by manufacturers. If the fluid looks bad enough perhaps a couple of rapid changes might be considered. If the fluid smells burnt and is really off color perhaps it either was never changed or the transmission has seen better days.

This area will probably have many different opinions by individuals. It is close enough to an oil thread type of thing.

I dont really understand I suppose..

"Every 30k miles doing three drain and fills of ATF resulting in fluid that is 80% pure (i.e. new)."

Does this mean when the 30K interval hits, I drain the transmission, then re-fill it. Then repeat that 2x all in the same sitting?

Yes...but after driving a little bit, of course, between each drain and fill to make sure the fluid mixes.

I would just change it at 30k, once. Drain the torque converter as well. New filter, fresh fluid, and you're on your way.

I have been doing OK changing the fluid every 30-50k in my nonMB cars.

FWIW-Chrystler wants you to change the differential gear oil every 12k with synthetic, which is ridiculous. The unknown age (at least 20k) that came out sitll looked fine during the last refresh.

Fact is, Chrysler does not recommend that universally. Suggesting that they do is ridiculous.

So you'd buy...like what 3 gallons of ATF? That seems like a lot and a waste of money.

I mean how often do you come up on 30K miles? Why not just do 100% of the fluid? I drive a lot, I'll hit 30K once a year. I've decided to just pay my mechanic to change it out. He only charges $150 or so.



For most fluid change intervals I would recommend just sending a sample off to a lab and see what they say.

Example, transmission fluid on my 300D. I did some work on the transmission at 241K. I didn't bother replacing the filter, just the fluid. The filters change interval was up so I had the whole thing done and sent in a sample... here the are results.

http://i.imgur.com/r6gC86T.png