Quote:
Originally Posted by JCL
My understanding of my last BMW automatic (2003 X5 3.0) was that no change interval was recommended. Having overhauled perfectly good transmissions that were only good up until a customer decided to change his transmission fluid, precipating a costly overhaul due to valve body contamination, I wouldn't touch it. It is very much like the oil change debate, there are people in both camps. Also similar to the oil change debate, I think the fluid life is not really the key issue. Transmissions can fail due to sensors as often as anything else (I think they get them from the same guy who builds the window regulators, and they are the common element between the GM and ZF transmissions). New fluid isn't going to help, and there is a small, but real, chance that a fluid change will cause a failure. Better to avoid it entirely IMO.
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The oft repeated story of 'that fluid change caused the failure' is a powerful one...(and why were you charging for an "overhaul of a perfectly good transmission" when all you needed to do was drop the valve body and clean it?)
So I disagree- fluid life IS THE ENTIRE ISSUE! Wear components within the tranny contaminate the fluid, and wear accelerates as the fluid breaks down.
The argument that 'it's those new-fangled electronic sensors' that causes tranny failure is, IMHO, specious. Again, you do not see perfectly normal trannies with just a bad sensor- you see worn and sludged transmissions. Yes, an occasional bad sensor- but you just replace that part and off you go.
But glad to hear this isn't an issue for your cars.
In the meantime, owners should change (not flush, change) ATF at reasonable intervals...not the irresponsible 100k mile interval that BMW recommends. (And while we are at it, how can BMW recommend it at 100k, and it is "safe" but doing it earlier- say 20 or 25k is, all of a sudden, a 'risk'???)