Automatic Transmission Fluid Changing Strategy -- Opinions Please

[Tiger]

All transmission fluid will have particulates... it is from the friction materials in the transmission. Mine was super dark brown with tons of particulates. No burn smell.

When you do the tranmission filter job, you will understand why it is pointless to be 'conservative'... there is just too much work and effort to do that little thing. Get under your car and see how much work you have to do to implement your plan.

[Victor]

Here's a reply from the NJ BMW club tech contact. Not sure, but think he's had pro repair shop experience:

Victor,

I get asked this question quite often. Fooling around with a 16-year-old auto trans with 139k and no service history is, to me, a crapshoot. I think I would leave it be.

There are other knowledgable BMW folks who disagree and who would tell you to try servicing the trans. Some recommend replacing one quart of fluid at a time. If you decide to fool with it that is what I suggest.

[BMW4LIFE]

Some may tell you to never touch it...but I have had GREAT luck changing mine!

Just make sure you do not FLUSH it!

I went to costco and bought a case of the Chevron Dex III and ordered a new filter.

I did an initial drain of the old fluid, closed it, poured new fluid in, closed it, and drove about 100 miles

Then I drained it, closed it, filled it, closed it, and drove another 100 miles

Finally I drained it, DROPPED THE PAN (both small and large), cleaned them out including the magnet, changed the filter, got a new gasket for small and large, filled it and Loved every second of the change!

Mind you that I did this when the car had 180k or so on it and I assume that it had never been changed before...now it shifts smoother than ever!

[whiskychaser]

Here's a reply from the NJ BMW club tech contact. Not sure, but think he's had pro repair shop experience:

There are other knowledgable BMW folks who disagree and who would tell you to try servicing the trans. Some recommend replacing one quart of fluid at a time. If you decide to fool with it that is what I suggest.

IMHO this is an urban myth and Bill R hits the nail on the head: if it fails after an ATF change it was going to fail anyway. Is the dirty ATF or swarf supposed to be holding it together?

[genphreak]

Remember BMW techs opinions come from working in a dealership, where they should do no wrong (else suffer their manager's wrath), and where more than 50% of the cars coming in are new, and most of the balance are there as they have a problem already.

I don't feel that such opinions are statistically accurate for our cars- they are not the same demographic (i.e. how many 20yo Bimmers get serviced/fixed at BMW now?).

[Bill R.]

Its definitely not a myth, i've run into it too many times on older fords. Speculation is that you get gunk buildup behind the old orings and pistons that help it to seal, when flushing the the trans fluid the detergent action of the new fluid cleans and removes this buildup and the old orings no longer seal , fluid pressure goes around them etc.... or the detergent action flushes buildup out of areas that are past the filter and the gunk moves into the valve body and plugs up pistons and solendoids that have very tight tolerances..... take your pick. Either way i've seen really gunked up transmisssions fail after the fluid change.... Odds are they would have failed anyway but the customer still tries to blame the shop/mechanic for the failure... In my mind if the customer suddenly decides to change the fluid at 150k when he never bothered to have it changed ever before then he or she has noticed some kind of symptoms that may have already signaled impending doom for the trans.

[Russell]

Remember BMW techs opinions come from working in a dealership, where they should do no wrong (else suffer their manager's wrath), and where more than 50% of the cars coming in are new, and most of the balance are there as they have a problem already.

I don't feel that such opinions are statistically accurate for our cars- they are not the same demographic (i.e. how many 20yo Bimmers get serviced/fixed at BMW now?).

That said, I trust Bill R's opinion.

[Victor]

With respect to both Russell and Bill's comments, the original question regarded developing a strategy for NOT screwing-up the trans when history is unknown. The concept of incremental fluid changes has been given sufficient pro / con discussion, but the trans fluid color / condition question less so. Red, black, particulate, metallic ... Each has some meaning.

In my case my indy said my fluid "didn't look too bad." I don't have records, but assume if it's not too bad that a change will extend its life. The plan as it stands is:

1. Remove a small sample of fluid. Note condition (which I'll report here). If not really scary looking, replace a quart. (I bought a pump for the purpose). Otherwise, the glop goes back in. (I wish I could properly check the level, but without a lift it's impossible as the trans will be crooked).

2. Assuming I've made a small replacement of some fluid, off I go on my test. Next replacement may be the same, or larger, depending on original fluid color and driving results.

3. After confidence builds, replace filter, gasket, and all fluid from the pan.

If the fluid is not awful, but not great either, I suppose there's the possibility of dislodging gunk once the new fluid's concentration reaches a certain point. Of course I could stop if I feel I've pressed my luck.

[BMW4LIFE]

I want to say that I get where your paranoia comes from but at the same time it still blows my mind how people will consider keeping 20 year old beaten fluid in the trans rather than pouring in clean fluid.

I hear what you are saying about it failing after the change, but like people have said before, if the NEW fluid RUINED your tranny, that ish was on its way out! Its like saying...My engine run...why should I change the oil? I mean, what happens if when i change it the engine blows up? Idk....I was very paranoid as well but after A LOT of research I noticed that the fluid changing wasn't the culparte here...rather the FLUSHING that is done under pressure. If you want to be REALLY REALLY cautious, I would do my procedure but one quart at a time...might take you longer than anyone would have patience for but the progression would be sooo slow that you wouldn't notice a difference.

Furthermore, if your tranny is held together by GUNK...well, better it fails on you when you expect it than when you are climbing the road 300 miles away from you house...

p.s. that is not suppose to scare you...

Change it and be done with it!

[Victor]

BMW4LIFE,

You got away with a full fluid change on a 180k trans! Quite impressive, flying in the face of conventional wisdom which holds that if you don't think it's been changed, as you assumed, don't change it (due to internal build ups which can become dislodged). Interesting that you say flushing can be the culprit. Why wouldn't the same logic hold, that flushing could only be good?

Again, in my case I don't know if it's every been changed, but I'll take a sample soon and see if I learn anything. The better it is, the more confidently I'll change the fluid.

Best, Vic