I know you are discussing using ATF in the engine to clean it out (and it works very well for that), but be careful as your caution about moving the particles around is pretty applicable to what happens when you change transmission fluid as well ;)

Yes, I know you recommend changing transmission fluid early, before anything collects there, but the humour struck me.

When I spill oil on my garage floor, I don't pour more oil in an effort to break it down and clean it up. I use a degreaser to break it down. Pouring ATF inside of an engine is going to breakdown the sludge that was caused from either improper oil type or servicing intervals. Draining and refilling the transmission w/ new ATF isn't adding a fluid that will cause breakdown of a dissimilar fluid because it's the exact same fluid. The only thing I'm doing is diluting the old fluid and making it stronger by adding new.

I understand where you're coming from in regards to dislodging sediment, sludge, etc...but that's my whole point. In either the engine (like the OP experienced) or the transmission...change the fluid frequently enough before it has the chance to collect and cause buildup issues, then it's a moot point. I've done plenty of transmission fluid and filter changes over the years, both on my own and customers vehicles. The amount of particules taken off the magnets tells me that all that metal floating around is just honing the fluid passages and making them larger, just like the Extrude Hone process people do on intake manifolds, throttle bodies, etc. Opening those passages, wearing away on the checkballs, and eventually clogging the filter as well is what (in my belief) is causing the transmission issues. I change the fluid before the transmission has a change to basically eat itself alive.

This is the way I see it...don't change the oil enough, and you'll be replacing your engine sooner than later due to fluid breakdown, sludge, premature wear due to poor lubrication on metal parts, etc. The same applies to the transmission, and I don't see why people find the transmission an exception to that rule. That's just my logic, but once again...to each their own. Naz24 mentioned that his SA said BMW has revised lifetime to be 100k. For the minor cost of fluid and filter vs an entire transmission and the labor involved to replace it, I still suggest 50k to all my customers.

I'm new here but I've been aware of this urban legend for quite a while.

You're ignoring the flip side. Perhaps there are many transmission failures which have been avoided because the fluid was changed.

Whether changing the fluid has benefit or not is, IMO, a moot point. If there is no downside, and none has yet been provided, why not spend a few bucks doing it?

ATF doesn't break down the sludge and move it around because it is a dissimilar fluid, it is because it has high levels of detergents (to make it last longer). ATF is just a lighweight oil with friction modifiers, detergents, and so on.

I agree that if you do it often enough, you will minimize the risk. You don't necessarily change the value equation, but you do minimize the risk.

I don't understand your point about all the metal particles in the fluid honing out the valve body. The fluid in those passages is essentially static, the fluid isn't coursing through there. Those are activation circuits for lack of a better phrase, or control circuits, not bearing journals.

I think the debate is coming to a close this time though, as Sunny just suggested that any benefit is moot, so one should just spend the money anyway. Not sure I get that logic, but what do I know? :thumbup:

For those that haven't read it, this was one of the better threads on the subject: http://www.xoutpost.com/bmw-sav-foru...intenance.html

I'm not going to argue if there is a benefit or not. Anyone who doesn't believe in lifetime fluids will see a benefit in changing the fluid.

There are two reasons why you would not want to chage the fluid:

1. You see no benefit to doing so.
2. The risk of doing so outweighs the benefit.

I have seen no evidence to support either of the above is true so I recommend replacing the fluid.

Hope that clears up the confusion my statement caused.

The difference between us is that I do think there is a downside to changing the fluid for the first time at higher mileage, so does JCL, who not only has personal experience working on transmissions, but also has extensive knowledge in lubrication and mechanical engineering, etc. Also, don't forget about Weasel (current tech at a BMW dealer as well as prior trans shop work), motordavid (family member is AAmco owner), and others...

I have actually heard of shops/dealers baulking on changing the trans fluid even when the owner was ready and willing to pay for the service. It seems like some of these places don't even want to touch the trans incase something happens after the fluid change. That way the owner can't blame the shop for the failure.

Good link. I missed that one. :thumbup:

That's fine. I do not. And without evidence to the contrary it will remain an urban legend in my mind.

I've spoken to my mechanic, who has 25 years repairing BMWs, about this issue. He doesn't feel there is any risk to changing the fluid. And he has done it many, many times.

Even JCL has qualified the risk as slight.

That is their right. I'm not surprised to hear there are some shops which believe this urban legend.