Lazy man's tranny fluid maintenance

[Weasel]

Originally Posted by JCL

In very general terms, what has improved over the past decade is programming that provides firmer shifts (less resulting heat and clutch wear), better transmission cooling, and more experience on the part of BMW as to fluid breakdown over time. However, that is all a side issue. It isn't about whether the fluid is better if it is new, it is about whether new fluid will extend the life of the transmission. I don't think it will. Transmissions will fail for many reasons, but old fluid hasn't been shown to be one of them. You would probably be better served by replacing all the sensors inside the transmission than the fluid. Even better would be to take the money spent on fluid replacements, and put it in a future transmission replacement fund.

Couldn't have said it better myself. Automatic transmissions will fail inevitably just by nature... clutch packs will wear no matter how new the fluid stays. What seems that it would make the most difference is the driving profile as it would be more directly related to clutch wear.

And on a side note, when the clutch discs do wear the clutch material gets suspended in the fluid which thickens the fluid and adds some hydrolic pressure. My last job before BMW was at a trans shop (R&I guy). You'd be amazed of the number or failed transmissions that came in shortly after doing a fluid change simply because the viscosity was lowered, the lubricity was higher, and the clutches just started slipping bad to the point of no return.

I can tell you that on my own personal vehicle, I will not be changing the fluid.