I worked in the dealership SOS lab many years ago. Can't do much with ATF. They can test for water, but you could see that without a lab. They can test viscosity, but that isn't a critical ATF spec. They could run a mass spectrometry analysis, but that is telling you about the component, not the fluid. It only provides valuable info if you run multiple samples over time and compare the wear rates. Not worth doing with this component, IMO, and definitely not worth doing once.

The most critical things about ATFs are the fluid friction modifiers (additives) for the wet clutch packs which differentiate the various fluid specs. But they can't test for those.

Fording creeks??? Is that a euphemism for car wash? :rolleyes:

I suppose during a flash flood we might actually drive through a deep puddle when a storm drain get blocked.

Joking aside, I'm not very impressed by the systems that are supposed to warn service is needed. We've had brake problems and the brake sensor didn't trigger. The type of stop & go traffic, couple with hilly terrain make me a firm believer in changing oil more often than 15K.

But what I was really driving at is why trans fluid is lifetime, but none of the other gear fluids?

Those other components are very different. No pumps with pressure lubrication, no filters, hypoid gears, no valve bodies. Transmissions have a very low lubrication requirement, you aren't changing it to lubricate it better. Old fluid lubricates fine. You are changing it to refresh the friction modifier additive package, deal with fluid oxidation, etc.

I changed the fluid and filter using our signature series ATF and OEM filter and the transmission feels much better. Shifts great, I've definatly abused it a bit slamming the kickdown once in a while to rev the engine (I also use it alot to pass slow motorists). But that's just my experience doing it at 99k miles. As some of the others have mentioned if your not having issues then there's no point in messing with it. If it ain't broke don't fix it. But if you do decide to change it, we are running a sale on our synthetics ;)

I would be very interested in hearing the results of such an analysis.

Two things:

1. I do not believe BMW holds this position any longer.
2. What is the definition of "lifetime"?

The latter is really the crux of the discussion. When I think lifetime I think a really long time. However, as mentioned in a couple of previous posts in this discussion, BMW considers lifetime to be the warranty period (or something along those lines).

You sure lifetime means just within the warranty period?

Well...no :D That's the problem. Lifetime is ambiguous. It's my opinion buyers definition of lifetime is considerably longer than the manufacturers. For example the manufacturer may consider the service life of the transmission fluid to be 100K miles. However we, as buyers, may consider it to be the entire length of time the vehicle remains operational.