Transmission fluid for BMW

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Dec 4, 2004
Lexington, KY
Just had a rebuilt trany installed in my 95 BMW 525i by my BMW specialist. It is the French made GM trany of dubious quality when new. The rebuilder (wholesale to shops only) filled it Castrol dex/merc and said it should only be filled with the same product when serviced. Do not change brands. Also do not use synthetic. Any opinions on this? They also suggested a drain and fill after 3,000 miles. Not necessary though. Opinion?
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I have added a Magnefine to 2 of my vehicles and a full flow spin on filter onto my Truck. If you shop around you can also add some high temp neodymium magnets to your transmission pan to help catch more materials. I like both magnefine and spin on systems. My opinion is that you should either get a Magnefine and change it out after 5,000 miles, then you can probably go 15,000 to 20,000 on the next. Or take a look into the full flow filter setups and change that out at a similar interval. Your rebuilt transmission will produce something like 90% of its break in materials over the first 30,000 miles. However the vast majority of that will be within the first few 1000. If you do get into aftermarket filters just be sure to check it regularly and change it out occasionally. Damage can result by forgetting about it. Hence why Ford no longer "authorizes" their use. They have to be changed out every 20-30,000 miles and it seems that most people drive a car, even with idiot lights on, until it dies. (However, being a Member of BITOG I seriously doubt anyone here has that issue.) Just realized I didn't answer your question. If they are using a Dex/Merc I think that you are safe to stick with any Dex/Merc fluid. There are many out there that would fit the bill. However, Castrol Dex/Merc is pretty good stuff. I've done research and I haven't ready any complaints on it. I've started researching the fluids currently carried at my Walmart and that is one of the non-Supertech brands they carry.
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i think it is solid advice! i would listen to the rebuilder. i wonder why no synthetic? maybe because they don't want the risk of highly friction modified fluid ending up in their rebuild?
Syn could be because of the elastomers used in the AT. Read about some incompatabilities running Dex VI. 3000 miles is to clean junk out. I would. Id consider running a maxlife D/M fluid, which I hear is good and actually meets (approved perhaps) the MB and BMW specs.
I'm with JHZR2. Also: Syn based ATF is blended with more or less to the same friction properties as to their non-sync ATF of the same specifications in order for A/T trannie to work properly. So, kinda makes you wonder where that idea RE: highly friction modified fluid comes from?? Q.
I don't know if it would work for your app, but Redline D4 ATF has served me well for over 100k combined miles in 3 different BMW's (2 M/T, 1 A/T). I keep it in for no more than 30k miles and often significantly less due to "track (ab)use" wink I think it is a very wise idea to change fluid at 3k post rebuild, as it will clear out a ton of metal shavings that will end up in the fluid after a fresh rebuild.
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