Originally Posted by ncsucarjock

I"m sorry you don't have the V8. One, I can't drive a manual, due to knee issues. 5 speed isn't an issue, so if you want to compare apples to apples, you have to do an automatic 3.0...

And then...lets put 6000# behind it, and head for the mountains. I think you'll find the 3.0 becomes very labored with that, manual or automatic. As I tow between 3000-7000 miles a year with that load... That's a pretty crucial measurement for me.

Back to the original posters question about changing fluid, this is all I can say. I've been through mechanics school...

No fluid lasts forever. They *all* break down. We know that transmissions are one of the most expensive items in a car, and yet, we dont' want to perform basic fluid changes because manufacturers have trained the public that "maintenance" is bad, and should be avoided - a perfect car would run perfectly forever, with zero maintenance. After coming back down to earth from the space dream, let's realize that all fluids - cooling, oil, transmission, differential, transfer case, power steering fluid, *all* degrade. There are recommended intervals for most of these. In my opinion (and this is *just* my opinion) regular fluid changes of all fluids are crucial to longevity. This does not mean I advocate 3000 mile oil changes, but I do recommend using some common sense.

I use this rule when it comes to automatic transmissions:
1) fluid breaks down, more in heavy use situations. Changing every 30,000 - 50,000 miles with a good quality compatible synthetic is a must do, regardless of what any manufacturer says.

2) fluid "flushes" are BAD juju. This is when they use a machine to pump your old fluid out, and new fluid in. The power for doing this is provided by the pump on the machine. I've heard of many instances where this procedure has damaged transmissions, probably due to excessive pump pressure.

3) If you disconnect the transmission line at the cooler, and start the engine, using the transmission pump to pump out fluid, this is an acceptable means of "pumping" the fluid out. This will allow a more complete fluid change, but it takes a lot longer, because you need to stop every 1/2 gallon (two quarts) and refill the transmission pan. On the BMW X5, at least on my V8, this is not easy to do. I prefer to just drop the entire pan, remove the filter, check for any excessive metal or sediment (and at 50k, I found none), replace the fluid, and call it good.

I will change again at 100k miles, and probably 150 and 200. For the record, for those that have changed fluid every 30-50k religiously, I've not heard of a transmission dying. If there's is one that has failed, I'd be pretty surprised, and willing to blame it on an improperly made part or assembly.

By and large though, transmissions are pretty simple devices. Sure, they have more gears, and electronic controls, but the basics have not changed since the first automatics came out more than 50 years ago. And regular fluid changes were required for decades before this whole "non-maintenance" scheme started appearing in the 90's.

For the record, I also change my engine oil every 10k miles, and the differential fluid every 50k, and the transfer case fluid every 50k as well. All of these are synthetic fluids, if they were conventional, I'd change more frequently, but I don't like conventional fluids, and dont' run them in any of my vehicles.

Also worth noting, changing your brake fluid every 2-3 years is part of required maintenance, and so is changing your antifreeze about the same time.

Do all this, along with plugs, filters, keeping it clean, attending to any leaks, and you'll be shocked how long a well maintained vehicle will run.