IMHO, flush the old out and replace with new. Wont hurt regardless of mileage or age. There wont be gunk in the transmission large enough to clog passages. If so, the trans is already done for.

I'm also pondering this as I'm nearing 74k miles and only a bit over 2k are mine. On other vehicles I have not been lucky with flushes but the X5's ZF is an entirely different transmission. I'm definitely going to change the fluid and filter.

Let's not confuse flush with change. No flushing machine should ever be connected to these transmissions. Changing the fluid requires dropping the pan which has the filter built into it. So a new pan/filter is part of the process. Get it hot, drain and refill taking care to follow OEM's recommendations regarding proper level at specific temperature. These transmissions should not be flushed period.

Where is this information coming from? Official ZF transmission service (i.e. in Germany and a few other places) will flush all the old fluid out. Included will be a filter change. Why would replacing ALL the fluid be a bad thing?

Lubehead has spoken a wise words.The information comes from experience,not manuals.Everyone is free to experiment on his car.

I would not touch it.But if you want keep digging or ask more competent mechanics.

This subject has been pounded to death since the inception of this site
and the conclusion of the matter after all things considered is to make
up your own mind but beware of the choice you make. The are lots
of results if you search the site but here's one that might help.
http://www.xoutpost.com/bmw-sav-foru...-lifetime.html

The reason this is a constant succession is that there is NO common definition of "flush".

You can have a reservoir of ZF fluid, and passively permit the trans to pull in new fluid and expel old fluid...OR you can attached a machine that forces non-ZF fluid through the trans. Both may be called 'a flush', but are vastly different.

Then you have mechanics that have made up their mind on 'who knows what definition of 'flush'... perhaps based on experience from tranny shops using powered machines or what not... the 'flush horror stories usually involve some level of 'not doing it right'... people wait until there are shift issues, then get a flush...or a shop does it wrong..or it is the famous Acura/Honda POS trans that the manufacturer blamed everything but themselves for the issues.

So like OE versus OEM versus aftermarket...nobody is using the same definition- it is impossible to have a rational discussion

IMO

That does seem to be a problem doesn't it. Round and round we go.
Where we stop no one knows….:rofl:

Agreed, "flushing" the trans properly is important. But, "replacing" all fluid is better than just replacing what comes out of the pan.

As for OE and OEM, they are two different things: Original Equipment (OE) means you get a manufacturers part (i.e. from BMW with BMW logo on it, or similar). Original Equipment Manufacturer (OEM) simply means the manufacturer that made a part for BMW made the part being sold. It may be different (slightly) than the part sold by BMW. Everyone probably knows that aftermarket is simply a part made by a different manufacturer than that sold by BMW.

So, a little transmission story (my experience). I have an E38 (5HP24, I think) with 228k miles on it now. The transmission is original to the car, but fully rebuilt by me once at about 202k miles. I changed the fluid at about 101k miles with (I think) Royal Purple full synthetic ATF. That fluid remained in the trans until about 171k miles until I had to pull trans to replace rear main engine oil seal. I replaced the trans fluid at the time with a fluid that escapes me at the moment (full compatible synthetic ATF). The transmission failure was due to the first gear drum lip failure. This is a mechanical part failure due to fatigue and a common issue with the 5HP24 transmissions. Upon disassembly of the transmission, all other parts were in excellent condition, including the steals that still showed original machining marks. The friction material was in good condition as well. I replaced the friction, but not the steels (talking clutch packs here). The other common failure mode is broken O-rings which allow fluid pressure to bleed off and resultant low fluid pressure cause shifting problems. And finally there is the reverse drum piston failure. These last two common problems were not evident in my transmission. So, after full rebuild, I filled with Valvoline Maxlife (full synthetic) and great shifting ever since. As an aside, the internals of my transmission had the usual grey coating/sludge on all parts, but nothing that bit of new fluid would dislodge to the point of plugging some of the orifices in the VB. Yes, I thoroughly cleaned off the grey "sludge" prior to reassembly.

It is my opinion (or otherwise) that the ZF Lifetime fluid is not required for the transmission to work properly or last properly. Yes, the ZF fluids are excellent in that it is a highly refined mineral oil that thus has high heat resistant properties (i.e. it does not break down due to heat as soon as other ATF fluids). This is why ZF states it is a lifetime oil (resistant to heat caused breakdown). The other conventional ATF oils probably do not have the longevity from heat breakdown as the ZF oil and thus should be changed more often (i.e. 60k miles). Also, IIRC, ZF oil was manufactured by Esso (or was/is it Shell). And, I think any highly refined mineral oil can be legally classified as synthetic. I am sure others will disagree, but my personal experience with owning BMW automatics for well over 3 decades (I currently have 5 on hand with ZF automatics) and nary and ZF failure attributable to oil changes (I change them all regularly) adds confidence in my methods (for me anyway). The only fluid related failure I have had was to a GM unit in my sons 323i. I think we cooked it during a day long autocross abuse session. The fluid was definitely burned and not ZF fluid. I pulled the GM unit and replaced it with a ZF unit (5HP19).

Sorry for being so long winded.