Quote:
Originally Posted by Weasel
The high mileage fluid changes are always iffy for the simple reason that the clutch packs in the transmission will wear no matter what, and the clutch material gets suspended in the fluid and alters the viscosity and friction profile. When you change the fluid the worn clutch packs are more prone to slippage and it can cause a transmission failure earlier than if left alone.
On the other hand, the fluid will break down slowly over the years and after a certain point it will be less efficient as a lubricant and a hydrolic fluid. It really is a lose lose situation, but the wear on the clutches causing slippage will surface faster after a fluid change than any problems caused by not changing the fluid. (in most cases)
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Yes - I've read that reasoning here before. But I guess my question is what is BMW's official position and what is behind it? When the 03 X5 was made, BMW recommended a 100K fluid change. I am under the impression that US BMW dealers are now telling customers the fluid is lifetime. But that is not what my service booklet says. So are the dealers getting this lifetime fluid recommendation from the actual factory as an official update, or did they come up with it on their own because they ran into some issues with complications from a fluid change causing issues?
And if the fluid change is $500, I am leaning towards keeping that as a downpayment on a rebuild if there is really no data from BMW and the trans mfgr to suggest a fluid change will provide any longer life. Should be somebody around in CA that can rebuild a ZF for $2500 or so.
But I do find it odd that BMW would change their position on this service. And I also find it rather coincidental that other car makers like GM that use the same trans (not to mention GM made the trans) are using the same 100K fluid change interval that BMW used to recommend. That also suggests 100K is not "high mileage", since that is the recommended fluid change interval.