Change automatic transmission fluid?

[MikeM.]

In BMW's case, transmission fluid at say 100k miles has valuable metal shavings in it that changing it out for new fluid would cause failure. That problem is avoided by just leaving the fluid alone or an earlier and then scheduled fluid changes which is what I'm doing.

I still don't have an opinion on changing transmission fluids because I've seen so much conflicting info and I simply don't know enough to have an opinion one way or the other.

But I will say your explanation above makes little sense. If the metal shavings at 100K miles are so "valuable" then wouldn't you want them to build up (and thus avoid changing it at all, even very early)?

[Kedis82ZE8]

I think this happens more often than it should-----> Wrong AT fluid is used during the service

This talks about flushing which I am opposed to but a few thoughts nonetheless

http://www.aa1car.com/library/2004/bf100456.htm

"Automatic Transmission Fluid Flush

Copyright AA1Car
Adapted from an article written by Larry Carley for Brake & Front End magazine

Flushing can prolong the life of a transmission, provided it is done fairly regularly, say every 30,000 to 50,000 miles. But if the transmission on a high mileage vehicle (say over 100,000 miles) has never been flushed, it is probably best to NOT flush the fluid. Here's why: The detergents in new ATF may loosen up accumulated crud inside the transmission, which could cause some problems within a few thousand miles or so after the flush. So if your fluid has never been changed and your vehicle has a lot of miles on it, it is probably best to just leave the fluid alone and top off the fluid level as needed if it is low."

[CX-5um]

I still don't have an opinion on changing transmission fluids because I've seen so much conflicting info and I simply don't know enough to have an opinion one way or the other.

But I will say your explanation above makes little sense. If the metal shavings at 100K miles are so "valuable" then wouldn't you want them to build up (and thus avoid changing it at all, even very early)?

I first came across the "metal shavings" explanation within a BMW forum I used to frequent. I thought that was a bit outrageous statement myself but reminded myself that these guys had much more knowledge than I had of the matter. Then I shopped around calling shops in the San Diego area where I lived at the time. Not one shop, not one BMW dealer was willing to take my money and change my BMW tranny fluid. The #1 question they ask me is what is my mileage. (It was around 90k miles). The #1 explanation they provided was that the metal shavings in the fluid was really important. They countered that had my mileage had been lower (40-60k miles) they would've serviced my BMW. (BMW dealerships do not do it at all).

To answer your question more specifically is a challenge. From my research I recall that an oil analysis of the BMW tranny fluid at 70k miles indicated the oil had a very different composition from new. This may have then accelerated the accumulation of metal shavings. This may explain why it is important to change the fluid prior to reaching this point. The following is from a Bavarian Auto blog. It mirrors the more technical explanation given to me by shops.

The only potential problem would have been with a transmission that was not serviced properly in the first place, which then has its fluid changed at something north of 100,000 miles. There is a possibility that crud that has built up in the valve body may be softened and dislodged …. only to jam another area of the valve body. Additionally, we feel (after seeing some of these transmissions, internally) that in cases where the fluid was never serviced, the old thick fluid that is laden with wear particles, is actually helping keep the worn-out clutch packs operating by sort-of filling in the voided area between the clutch plates (the fluid in these transmissions looks like a non-synthetic oil that would have been drained from a 300,000 mile old engine, after being run in the engine for 20,000 miles …. with sand added to it). Replacing with fresh fluid just makes the transmission act as it normally would with that much wear. If the transmission were in a state of wear that would cause it to start slipping shortly after a fluid change, it would likely not have lasted much longer anyway. Of course, the wear would not be to this point if the fluid had been changed regularly in the first place!

So basically this is what I got.

1. The non-serviced high mileage transmission oil may develop crud.
2. The non-serviced high mileage transmission oil is thicker and laden with wear particles (shavings).
3. The transmission parts have deteriorated and actually rely on said crud and metal shaving laden oil to fill voids and to operate.
4. Changing the metal shaving laden fluid and removing crud allows the transmission to operate as it should WITH wear. No matter what that wear is present.
5. The transmission now with new fluid will simply act like a transmission with wear would. Depending on the level of wear, the transmission will either operate poorly or possibly fail despite having new fluid.

Options: A. Leave transmission oil alone and run till it stops working. It may last you another 1k miles or may last you another 100k miles. Who knows? Chances are you'll sell the car and it would be the next guy's problem. B. Get a new transmission. Those shops were right in telling me option A. Option B was a last resort well unless selling the car. There's option Z which is to service the tranny fluid on a set schedule and avoid this whole mess.

[Unobtanium]

I still don't have an opinion on changing transmission fluids because I've seen so much conflicting info and I simply don't know enough to have an opinion one way or the other.

But I will say your explanation above makes little sense. If the metal shavings at 100K miles are so "valuable" then wouldn't you want them to build up (and thus avoid changing it at all, even very early)?

Whatever his explanation, it's legit in cause--->effect. You change fluid at 100K miles, and you would have saved time and money just dropping the trans and replacing it. Because now you're going to be doing that, AS WELL, shortly.

[MikeM.]

So basically this is what I got.

1. The non-serviced high mileage transmission oil may develop crud.
2. The non-serviced high mileage transmission oil is thicker and laden with wear particles (shavings).
3. The transmission parts have deteriorated and actually rely on said crud and metal shaving laden oil to fill voids and to operate.
4. Changing the metal shaving laden fluid and removing crud allows the transmission to operate as it should WITH wear. No matter what that wear is present.
5. The transmission now with new fluid will simply act like a transmission with wear would. Depending on the level of wear, the transmission will either operate poorly or possibly fail despite having new fluid.

Interesting explanation. By this line of reasoning, it would be beneficial to change the fluid often early in the transmissions life but, at some unknown point, stop changing the fluid so the old fluid can extend the life of the nearly worn out transmission.

[CX-5um]

Interesting explanation. By this line of reasoning, it would be beneficial to change the fluid often early in the transmissions life but, at some unknown point, stop changing the fluid so the old fluid can extend the life of the nearly worn out transmission.

The theory is a scheduled transmission service helps minimize transmission wear depending on the lifespan of the actual fluid's integrity. Wear will always occur so the goal is to minimize that wear by changing the fluid. Something like an every 40k schedule. You don't have to stop and should be able to extend it to like 200k miles+ because the amount of protection provided by periodic fluid changes allows for less wear as compared to 100k miles with no fluid change at all which at that point is a crap shoot depending on the existing wear. If the wear isn't too bad then the 100k initial fluid change is good....but if there was significant wear then don't be surprised if the transmission fails shortly thereafter. I think a good (and serviced) transmission should last into 200k miles. We here folks all the time with 200k miles on original non-serviced transmissions. But then what type of transmission is it? Is it a real simple design? The Skyactiv transmission from what I read is complex and has multi-plates that act like a dual clutch transmission . More complex transmissions from what I read require servicing.

[yrwei52]

This:

I think this happens more often than it should-----> Wrong AT fluid is used during the service

plus these:

1. The non-serviced high mileage transmission oil may develop crud.
2. The non-serviced high mileage transmission oil is thicker and laden with wear particles (shavings).
3. The transmission parts have deteriorated and actually rely on said crud and metal shaving laden oil to fill voids and to operate.
4. Changing the metal shaving laden fluid and removing crud allows the transmission to operate as it should WITH wear. No matter what that wear is present.
5. The transmission now with new fluid will simply act like a transmission with wear would. Depending on the level of wear, the transmission will either operate poorly or possibly fail despite having new fluid.

should be the proper guidelines for automatic transmission fluid change. But calling "transmission oil" is something I don't get used to...

BTW, I was totally surprised to find out the 5-speed Steptronic automatic transmission in our 2000 BMW 528i was actually made by GM.

The other funny thing I'd found out was VW's OEM automatic transmission fluid has 2 years of shelf life stamped on the bottle. In the mean time they claimed their auto tranny has life-time fluid and fluid change is not needed!

[CX-5um]

This:
plus these:
should be the proper guidelines for automatic transmission fluid change. But calling "transmission oil" is something I don't get used to...

BTW, I was totally surprised to find out the 5-speed Steptronic automatic transmission in our 2000 BMW 528i was actually made by GM.

The other funny thing I'd found out was VW's OEM automatic transmission fluid has 2 years of shelf life stamped on the bottle. In the mean time they claimed their auto tranny has life-time fluid and fluid change is not needed!

Yeah BMW at that time used 2 or 3 different transmission suppliers. GM and I think ZF. Can't recall the third.

VW had a recall on their DSG transmission a few years ago. They offered 100k warranties on repaired ones with the condition that owners have transmission fluids changed every 40k miles otherwise warranty won't be honored. This is not your typical DIY job nor cheap. $400-$500 at dealer, about $250 in DIY parts/tools. Mazda's transmission fluid drain/fill or heck even flush is much much cheaper. A drain/fill is an easier DIY job.

[yrwei52]

Mazda's transmission fluid drain/fill or heck even flush is much much cheaper. A drain/fill is an easier DIY job.

I thought Mazda OEM ATF is pretty expensive too?

[Kedis82ZE8]

I thought Mazda OEM ATF is pretty expensive too?

I think around $15/quart and a drain/fill is around 5-6 quarts.

[4G63T]

Doesn't make sense how metal shavings is good for the transmission on those BMWs . I'm thinking something else is a culprit of changing the oil at high mileage causing the transmission to fail .

Hypothesis :
Maybe as time and repeated heat cycles and changing weather and wear particles the oil viscosity gets thicker ? As mileage gets higher with the oil, the gears begin to wear more then they should and the tolerance is not as tight as it was , requiring thicker oil . And when people put in the "correct" oil viscosity , at that high mileage the required viscosity is too thin for it now .

But when changing the oil early consistently , the gears don't wear as fast or as much . So the recommended oil viscosity is sufficient for the still "tight" gear tolerances .


Oil over time, changing weather cycles, normal friction heat cycles, water condensation mixing etc... loses it's properties to lubricate and protect etc... Gear Oil does not get better over time and usage.

What you guys think ?

[Unobtanium]

I think around $15/quart and a drain/fill is around 5-6 quarts.

$15 a quart, and 12 quarts. This is what the Mazda dealership quoted me. $312, IIRC. I'm going to have it done here in a few weeks because it's still under warranty, and "why not?" If it doesn't kill it, it will help it. If it kills it, I get a new one for free, soo....

[Unobtanium]

Doesn't make sense how metal shavings is good for the transmission on those BMWs . I'm thinking something else is a culprit of changing the oil at high mileage causing the transmission to fail .

Hypothesis :
Maybe as time and repeated heat cycles and changing weather and wear particles the oil viscosity gets thicker ? As mileage gets higher with the oil, the gears begin to wear more then they should and the tolerance is not as tight as it was , requiring thicker oil . And when people put in the "correct" oil viscosity , at that high mileage the required viscosity is too thin for it now .

But when changing the oil early consistently , the gears don't wear as fast or as much . So the recommended oil viscosity is sufficient for the still "tight" gear tolerances .


Oil over time, changing weather cycles, normal friction heat cycles, water condensation mixing etc... loses it's properties to lubricate and protect etc... Gear Oil does not get better over time and usage.

What you guys think ?

The cause doesn't much matter, IMO. The results do. The results are a dead tranny, and I don't mean Jenner.

However, I do think it's more about friction coefficients and clutch bands and fluid viscosity and detergents and valve-body passages and sludge...

[Kedis82ZE8]

$15 a quart, and 12 quarts. This is what the Mazda dealership quoted me. $312, IIRC. I'm going to have it done here in a few weeks because it's still under warranty, and "why not?" If it doesn't kill it, it will help it. If it kills it, I get a new one for free, soo....

If one was doing a flush but not for a drain/refill. IIRC Chris mentioned only about 5-6 quarts comes out on a drain.

[Unobtanium]

If one was doing a flush but not for a drain/refill. IIRC Chris mentioned only about 5-6 quarts comes out on a drain.

The dealership that is doing it has a machine by BG (*?) and they remove the trans lines, hook it up, and it pulls out 12 quarts, and puts in 12 quarts. Whether the 12 it pulls out is 6 of the new it put in, I have no idea. That just is what it is.