X5 4.4 - Sludge in engine and oil filter housing... help!

[JCL]

Originally Posted by sunny5280

This is just a restatement of the post FSETH linked to. There you said you felt the chances of dislodging sediment are slight. I agree with this. There is a possibility but I don't see it being very high. Nor do I see any evidence the dislodged sediment, in the slight case it occurs, results in transmission failure.


I am assuming you're replacing the fluid with the recommended fluid. Which makes this point moot.

It is not just a restatement. The chances of a fluid change causing a transmission to fail are slight, but still very real. You have to weigh that against the benefits of clean fluid. What makes you think that clean fluid will make the transmission last longer? There is no data to support that point of view. I say the chances are slight, because posters regularly change their fluid, don't have a failure, and then conclude that this is proof it was a good idea. It isn't proof, it is simply proof that they dodged the bullet, and good for them in that case. I won't change my own transmission fluid because I see no reason to. The transmission failures we have seen haven't been caused by worn out fluid.

Talk to anyone who has worked in a transmission shop, and they will confirm that they regularly get overhauls caused by unneeded fluid changes. Doesn't happen with every fluid change, but it is a very common failure mode. Sludge that wasn't hurting anything gets flushed into the valve body when you refill it and restart it, on the initial pressurization; that sludge then clogs an orfice, and causes an actuator or sensor to fail.

If you are replacing the fluid, I assume you are using the correct fluid specification. That doesn't make my point moot, however, as fluid changes viscosity over time. That is known to the engineers, and the transmission adapts to the fluid as it ages. There are feedback sensors on things like clutch delays, etc. When you put thinner (correct, but still thinner) fluid in, you can get failures. Again, transmission mechanics are familiar with this. It has been discussed on this site by BMW techs.

All of this said, do whatever makes you happy. If you think you want to change the fluid, just change it. If it causes a transmission failure, you can always tell yourself that it was going to happen anyway, and that you didn't initiate it. If it doesn't fail, you win as well.