I actually read through almost all of this thread.

This is a really good thread, in that, anyone who doesn't have a firm opinion on whether they should or should not change their transmission fluid (especially at a high mileage), ... who ends up finding this thread through a search and reads through this thread.... will most definitely NOT change the transmission fluid, based on the materials presented by both sides AND the manner in which they were presented.

Then they would being doing so against sound advice and favoring an urban legend.

Well, I probably should just drop this, but why is that any more of an "Urban Legend" than the "Urban Legend" that changing your AFT will make your transmission last longer?

I guess I am saying that the term "Urban Legend" is a bit strong and misleading in that context. I would position it more as "debatable and supported only through anecdotal reports, which are not statistically significant."

Which could also be said of the other side of the argument.

P.S. I promise to shut-up about this topic after this post. :D

When this post hits 1,000 I am going to personally call the Castrol dipstick guy to come to each of your homes and whip you on the back of the legs.

Arguments pro "change the ATF":

• BMW recommends it at 100K mile intervals.
• No fluid is lifetime. Lifetime being defined as never change.
• Fluids act as a detergent and become dirty with use.
• The protective qualities of lubricants breaks down over time.
• Every other fluid in the vehicle is subject to change at regular intervals.
• Other vehicle manufacturers recommend ATF changes.

Arguments con "change the ATF":

• In 2002 Mike Miller, head technical editor of BMWCCA, made the recommendation to avoid ATF changes due to his observed increase in subsequent transmission failures.
• Numerous web sites making the same recommendation as Mr. Miller.

So we have facts for pro "change the ATF" (I put this in quotes because my argument has never been to change the ATF but more it doesn't hurt to do it) and opinions on the con "change the ATF".

In 2009 Mr.Miller appears to have reevaluated his 2002 recommendation and no longer has the passion for it he once had (but does continue to say there is a risk). As for the numerous web sites I suspect they picked up on Mr. Millers 2002 recommendation and ran with it. And now discussions on this subject make references to one another (it happened in this one) in a form of circular support (I've seen this happen too many times).

Many disagree with my urban legend label but that's how I view it. An unsupported claim has been made and repeated ad infinitum and taken on a life of its own. So much so that people making it feel threatened when someone dare question it.

Comments included above in red.

I should clarify that I don't necessarily think that ATF should never be changed, or that it should always be changed. I do think that readers should make their minds up after understanding the risks and rewards. There is no conclusive data either way. There are reasons to change the fluid, and reasons not to. Readers making an informed decision after understanding the two sides is far better than blindly changing it because it is somehow supposed to be done.

My responses in blue.

It seems we've been agreement the entire time.

Yet the con "change ATF" people act as if there is. My position is, and always has been, there's no data to show a correlation between changing the ATF fluid and subsequent transmission failures. Therefore it's an urban legend, folklore, wives tale, what-have-you.

Others have noted that your continued use of the phrase 'urban legend' is somewhat misleading. I agree with this observation. It is an urban legend to you because you have never seen it, and are not familiar with the workings of an automatic transmission. If I have seen examples firsthand that persuade me that there is a risk that outweighs the rewards, and at the same time I don't even know who Mr. Miller is but rather rely on my own experiences, it doesn't feel like an urban legend. Anecdotal, perhaps. However, many things in life are based on professional judgement, as opposed to internet heresay.

MD was correct in that this is a little like a high school debate. The purpose of it to me, though, is to show both sides of the argument, so that future readers can make their own minds up and not rely on the old wives tale/urban legend/etc that all fluids are worn out soon after being installed. I think we are probably accomplishing that.

:iagree: As anyone can see from my first post in this thread where all I was trying to do was let people know there are possible risks. I personally think it is worth letting people know. Like I said, I didn't realize this myself until shortly after buying our X in 2007.

Simply put, I will be changing my fluid and filter at the same time I change the friction materials or other components in my transmission.

Regardless of whether you change the fluid every 100,000 60,000 or 3,000 miles the friction material on the plates will inevitably wear, as will the electronic solenoids/valves and the rubber components. The fluid does break down over time, but the nice expensive synthetic fluids used in modern transmissions like in BMWs lasts a really long time before losing its lubricating and hydrolic properties.

If the fluid was overheated by repeatedly towing heavy loads then it can lose it's viscosity and should be changed, or if you have a component fail that spreads metalic debris that suspends in the fluid and clogs the filter. Lots of times the metal particles are tiny enough to flow through the filter and stay suspended in the fluid which is bad for all other moving parts.

The reason transmissions can fail if the fluid is changed at a higher mileage is simply because the worn off friction material is tiny enough to flow through the filter and stays suspended in the filter, adding to the viscosity of the fluid which adds hydrolic pressure, as well as adding to the friction between the plates. When you change all that fluid with fresh new fluid the extra friction/grip in the plates is gone and replaced with fresh slick fluid as well as slightly lower hydrolic pressures pushing against the plates... which all adds up to cause slippage, thus transmission failure needing rebuilding.

There is no proof or solid documentation depicting this because each and every transmission will be an individual case of wear and other variables due to the use and driving styles of different people. If you are considering whether or not to change your transmission fluid I would strongly suggest taking a small sample of about half a pint or so to inspect. You can look at it stirring it under bright light to inspect for presence of worn metal components. (will look like metal flake in a paint job) Same for presence of clutch material. (dull gray material, like graphite powder) as well as smell the fluid to see if it smells like tranny fluid (kind of a gear oil smell in BMW's case with the lifetime fluid) or if it smells burnt from overheating/overworking.

Basically you should look at the fluid in each individual case and get as many facts as possible from the fluid in each particular case to get a better idea, and thus make a judgment call from knowledge, not blind beliefs.

my 0.2c over :D