|
Agree completely that we don't have enough information to do a precise payback calculation. But if it can be shown that the cost and benefit lines diverge, ie that they never meet in practice and so there is never a payback, then it doesn't need to be precise in order to have some value in guiding our choices.
Nobody said the fluid was going to last the lifetime of the X5. It never referred to the vehicle's lifetime. We are talking about the transmission's lifetime. And the reason BMW said not to change it is that statistically, the transmissions failed before the fluid wore out. That is the essence of the argument that there is never a payback. That you can change it all you want, but it is more likely to fail for non-fluid related causes, so unless changes are free, doing them as PMs is a questionable proposition.
Again, the fluid doesn't get better as it ages. But it can be argued that the lubricating qualities of the fluid, being just one of its key characteristics, do get better.
If you refer back to the maintenance philosophy document I attached, it points out that in complex systems, failures often aren't more likely with age. That isn't intuitive either, but it is more and more true these days. So the maintenance practices based on older paradigms often don't make economic sense. All that said, if I was putting significant shots of nitrous into my X5 and thus operating its transmission beyond the design parameters, I would probably be changing the fluid regularly too.
__________________
2007 X3 3.0si, 6 MT, Premium, White
Retired:
2008 535i, 6 MT, M Sport, Premium, Space Grey
2003 X5 3.0 Steptronic, Premium, Titanium Silver
2002 325xi 5 MT, Steel Grey
2004 Z4 3.0 Premium, Sport, SMG, Maldives Blue
|