Personally? Because I have the experience to know how to change my coolant, bleed the system, and so on. I can manage the risks, and thereby mitigate them. That is something that I can't do with a transmission fluid change, unless I remove and tear down the transmission as part of the fluid change (which would be silly, since it is purportedly what we are trying to avoid)

The downside I was thinking of was the environmental disposal risk of the old coolant. It is a negative, but manageable.

I agree with you and your points; you can't correlate those fluids, and I am not comparing them. I think you misunderstood my comment. What I was trying to say is that some people speculate that BMW painted themselves into a corner in calling something "lifetime fill" and so to get out of that corner they changed it to "100,000 miles." My point is that I don't that's quite what happened since BMW clearly did just the opposite roughly around the same time, albeit for a different fluid (that actual fluid not being the relevant point of my comment).

IOW, they got themselves out of a corner (lifetime ---> 100,000) but then put themselves right back into a corner (4 years ----> lifetime) !?!?

Hope that makes sense.

I can agree with your logic. The whole point of my first post in this thread was just to let people know that there ARE risks associated with doing so on an un-maintained automatic trans with higher mileage. It seems important for BMW owners because many people do follow the factory maintenance program, which means there are a ton of BMW owners who either haven't changed their fluid or are planning on doing so for the first time at 100k. Unfortunately, these people fall into the catagory Mr. Miller describes where he has seen many fail after the change. That is all I wanted to point out. I didn't realize this myself until a year or two ago. I was under the impression that new fluid would be 100% beneficial with absolutely NO downsides what so ever. Seems that isn't quite true.

If I buy a low mileage car with an automatic transmission , I will consider changing the fluid out regularly, if nothing else than to make mysellf feel good. My X has 112,000 miles, so I am not going to touch it at this point. Might as well put that money into a rebuilt transmission fund instead.

My next car is going to have a manual anyway, so most of this debate will be inconsequential.

I am not going to provide you with data which isn't mine. Sorry.

You are choosing which words to focus on. I said it was slight, which means that it happens sometime. I called that X, earlier. We both seem to agree that X is more than zero. I said it was more compelling than Y. Now, where is your proof for Y, namely the benefit of changing the fluid, being anything greater than zero? Motherhood isn't a reason, just like hope isn't a plan.

I am basing my judgement on my experience. You seem to be basing yours on internet debates.

You use the phrase strawman, but then you provide all these tangental causes that have nothing to do with the debate. Let's stay on point.

Recommend you consider an applied failure analysis course. They taught us to look for root causes, and not be bullied by opinion.

I believe you are right. When I said they changed from "lifetime" as in never to "lifetime" as in 100k miles, I wasn't necessarily saying that they changed the interval for specific models, but rather that the interpretation of "lifetime fill" changed at some point. I think it happened somewhere from the mid 1990's-2002 or so.

Makes perfect sense :thumbup:

In the maintenance procedures checklists going from year to year you can easily see how and when changes were made. i.e. brake fluid 1 year ---> 2 years. Coolant 2 years ---> 3 ----> 4 ---> lifetime. etc.

Here's one example using coolant.. At the top is the maintenance procedure for 2002 X5's. In the middle for 2003. At the bottom for 2004, 2005 X5's. Similar information can be found if you compared details in service booklets from model year to year.

I remember first noticing this sort of thing year ago when they went from yearly brake fluid changes to q2 years. I had always done it yearly, and never thought about deviating from that schedule, but like JCL put it maybe there was something to it that I didn't know. So I got a brake fluid tester (FTE) and measured the brake fluid every few months. At around 14 months although the fluid was noticeably darker, it still measured less than 2% water content which was acceptable and according to the tester, not requiring a change. Nevertheless I still had it done under free maintenance.

So the risk exists and is real. Applying the same logic you use for the transmission fluid you would never change your coolant.

How to put this nicely.....You appear to have a reading comprehension challenge. Look up the word mitigate, and then see if you want to edit your post, above.

What do you mean it's not yours? Didn't you argue, based on your experience, that changing the transmission fluid is likely to result in a transmission failure?

X is greater than zero. And Y is greater than zero if you don't buy into lifetime fluids (do you?). The question is: Is the benefit of Y greater than the risk of X. I believe it is.

Why there is that experience referenced above. If you're going to argue your experience then you're going to have to provide the supporting data behind it. You can't have it both ways.

As for what I'm basing my argument on it's not based on internet debates. It comes from a number of things:

1. My mechanic who has been working on BMW for 25 years and has performed numerous transmission fluid changes without any failures as a result.

2. The fact there is no such thing as a lifetime fluid. We change every other fluid in our cars so why would the transmission fluid be any different? We know fluids become dirty and break down with use and age. This decreases the protection they offer.

3. The service recommendations of other manufacturer transmissions. Automatic transmission essentially all work the same way. Why would BMW transmissions be ommitted from fluid changes whereas other manufacturers would not?

There's nothing tangential about them. Is it your opinion the wrong fluids could not cause failure? Or improperly performed work could not result in failure?


I'm trying to find the root cause but so far you've avoided providing it. The claim is yours therefore the burden of proof is yours.