Trans fluid change update.

[JCL]

Originally Posted by HPIA4v2

No expert but this is the funny thing that to me is illogical:

consensus:
we know that sludge/particulate in high mileage car if disturbed by changing the trans-fluid can clog the passage ways in the valve body, so why is it OK to have the same fluid (with sludge/particulates swimming in it) to be kept until trans fail.
Wouldn't it be better if we change the fluid more often to avoid sludge/particulate to develop?

Transmission fluid has a high concentration of detergents in it. And the sludge isn't in the fluid, it is deposited, either in the pan or the filter. When you put in new fluid, you add fresh detergents, which clean out the passages, and move the sludge that was sitting there not hurting anything. That is the concern of those in the "don't change the fluid" club.

Changing the fluid more often doesn't avoid the particulates developing, they are primarily friction materials from the clutches that accumulate in any case. Changing the fluid simply provides more of an opportunity to move them around. If you change the fluid very frequently, you will keep on top of it. Or you can not change the fluid, and just let them sit there, it is the same difference.

[HPIA4v2]

Originally Posted by JCL

Transmission fluid has a high concentration of detergents in it. And the sludge isn't in the fluid, it is deposited, either in the pan or the filter. When you put in new fluid, you add fresh detergents, which clean out the passages, and move the sludge that was sitting there not hurting anything. That is the concern of those in the "don't change the fluid" club.

Changing the fluid more often doesn't avoid the particulates developing, they are primarily friction materials from the clutches that accumulate in any case. Changing the fluid simply provides more of an opportunity to move them around. If you change the fluid very frequently, you will keep on top of it. Or you can not change the fluid, and just let them sit there, it is the same difference.

So the transmission is really just design with defect built in, like a gene in some human where a blood clot can develop, dislodge and plugs artery killing the man (happens more to man than woman for example).
So any moment any of us can have trasmission failure due to this particulate dislodging and plug the valve body opening and nothing we can do about it, great design by ZF.

[blktoptrvl]

Makes me wonder why manufacturers don't install and require finer external filtering.

[JCL]

Originally Posted by HPIA4v2

So any moment any of us can have transmission failure due to this particulate dislodging and plug the valve body opening and nothing we can do about it, great design by ZF.

A couple of points. The particulate is unlikely to dislodge, there is nothing to make it dislodge. Power flushing it may do so, and occasionally, adding fresh high-detergent transmission fluid can cause it, but it isn't very common. And you can't blame ZF, it isn't unique to their transmission design. You could blame GM, since they invented the automatic transmision 70 years ago or so, and it is common to all automatics, but why bother?

[JCL]

Originally Posted by blktoptrvl

Makes me wonder why manufacturers don't install and require finer external filtering.

From a fluid standpoint, that is absolutely correct. You would get cleaner fluid, a simpler way of changing it, and much better filtration. Win-win.

Now the downsides. First is cost. Second is, transmissions haven't been failing due to fluid quality. They fail for a myriad of reasons, but we don't have burnt fluid as a cause in the ones that have been reported. So yes, we could have better filtering, but to what end? It is a solution in search of a problem, not that BMW haven't gone down that road a few times.

[blktoptrvl]

Originally Posted by JCL

From a fluid standpoint, that is absolutely correct. You would get cleaner fluid, a simpler way of changing it, and much better filtration. Win-win.

Now the downsides. First is cost. Second is, transmissions haven't been failing due to fluid quality. They fail for a myriad of reasons, but we don't have burnt fluid as a cause in the ones that have been reported. So yes, we could have better filtering, but to what end? It is a solution in search of a problem, not that BMW haven't gone down that road a few times.

Why do you mention cost? Is ATF that much more expensive than oil (my first automatic)?

I hear what you are saying about a solution looking for a problem; but if it cost me an extra $150 or so a year to change tranny fluid, that wouldn't stress me at all; especially on a vehicle this expensive.

[c4racer]

BMW used to recommend driveline fluid changes every 30K miles. Probably if you followed that it would still work great. But that only works for the original owner who keeps one for a long time, which is not typical. These days it is more likely for the first owner to be a 3 year lease. The second owner then buys it as a CPO and keeps it 2-3 years. And the 3rd owner is buying a 6 year old car with 80K miles on it and the trans fluid has never been changed. I believe at that point you are better off leaving well enough alone. I suppose if changes had been made every 30-50K that would be another matter. The only car we currently have that we bought new is a 2003 Mazda that is my wifes car. I changed the trans fluid at 50K, 100K and 120K. The last one only because I was replacing the engine at the time so pretty much had to. I will change it again at 170K. I figure 50K is a pretty reasonable AT trans fluid change interval.

But in my X5 and 740i that I got at 90K miles a piece, I am not planning to touch either one. Let it ride and hope for the best. The trans may well fail, but more than likely if it does the reason will not be the fluid. And changing the fluid now could cause trouble. So I feel the odds are better in not changing it once you get that many miles and no changes have been done. I don't buy into the 100K mile service interval. I say you either do it every 30-50K miles from new, or don't do it at all.

[FSETH]

Originally Posted by c4racer

But in my X5 and 740i that I got at 90K miles a piece, I am not planning to touch either one. Let it ride and hope for the best. The trans may well fail, but more than likely if it does the reason will not be the fluid. And changing the fluid now could cause trouble. So I feel the odds are better in not changing it once you get that many miles and no changes have been done. I don't buy into the 100K mile service interval. I say you either do it every 30-50K miles from new, or don't do it at all.

Exactly how I feel.

[JCL]

Originally Posted by blktoptrvl

Why do you mention cost? Is ATF that much more expensive than oil (my first automatic)?

I hear what you are saying about a solution looking for a problem; but if it cost me an extra $150 or so a year to change transmission fluid, that wouldn't stress me at all; especially on a vehicle this expensive.

It would cost BMW more to install finer external filtering, which was your suggestion. And any cost, even a small one, is too much if it doesn't do anything to prolong transmission life. If we saw failed or burnt fluid, and transmissions failing due to that failed fluid, then it would all be justified. But as long as transmissions aren't failing from not changing fluid, even ten years after they came up with the recommendation to leave it in for the lifetime of the transmission, every day that passes it is proving out the theory of the original design team, the ones who said just leave it alone.