Doing a complete ATF drain?

[unDummy]

All ATF that is pumped comes from the pan. But, the cooler does not see all the pumped ATF. Much is used and wasted back to the pan. The cooler gets surplus flow. Also, the ATF pickup isn't touching the bottom of the pan. So, there is even more old ATF in your transmission then you want to believe when doing a stand alone cooler line flush without dropping the pan or pulling the drainplug.

Because the pan has old/new ATF mixing, and because the TC has old/new ATF mixing, it is more beneficial to start with new fluid somewhere, otherwise you'll waste gallons trying to flush out old fluid that is constantly mixing with new fluid in multiple places. This is why the pan drop(or drainplug drain/refill) should be done prior to starting a cooler line exchange.
Its like making coffee and grabbing the cocoa by mistake.
Do you dump out the full cup of cocoa and start over(TC drainplug and pan drop) which is super effective, or do you dump out half the cocoa and constantly overfill the cup with coffee until you are satisfied that the cocoa is gone(effective but you wasted a couple cups of coffee), or do you just overfill that full cup of cocoa with coffee until you are satisfied that enough of the cocoa is gone(not too effective and pots coffee wasted)?

Also, how much ATF did you remove or actually use? If you are not pumping plenty of ATF through the cooler line, you are just wasting time and should just use the drainplug. 9 quarts(typical capacity) of dirty ATF(cocoa) will take plenty of new ATF(coffee) to remove. This is why typical ATF flush machines run 12-20 quarts of ATF.

There is really nothing to understand. You need to waste plenty of fresh ATF to remove old ATF using the cooler line. If you have the means of removing any old ATF without mixing(drainplugs), then do so.

 

[BrianL]

I did use the drainplug, as mentioned more than once. But I don't see how that would make any difference(?). I drained 3 quarts from the drainplug, then filled with 3 quarts. But, and this was part of my whole problem, what I poured back in the dipstick tube went to the pan, and I just flushed a good percentage of that right back out the cooler line.

So then, going by what you've said and what I've seen, using the cooler line is absolutely useless. I wonder how many people that use this method, and who's vehicle's cooler line pumps from the pan, actually know this. Being that, they way I understand it, using the drain plug accomplishes the exact same thing, and is probably safer since you dont have to run it while it's low. Drain pan, fill, run awhile, repeat. Again, I would have done this myself if I'd started many miles ago.

 

[ConfederateTyrant]

Quote:

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As far as your 2nd paragraph, if I pumped 2 quarts, and then only got 1 quart from the pan drain, that would show that I'm pumping from the pan, as I have described. Or is that what you meant? Not sure what you meant by 'we', you/me or you/others.

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No, if the fluid were to have the "reverse" flow, then the pan would fill up from fluid from the transmission internals. So you'd pull 1-2 quarts from the pan, but then that same amount of fluid would flow to the pan and fill it back up. So you'd get 3 quarts via a plug. This is ONLY with the method you are thinking is happening (I'm not saying it is not happening, just not very sure that is)

With the method that I, unDummy, and sky jumper (this is who my "we" remark was referring to) are suggesting, would be that it would pump out 1-2 quarts out of the pan, to the internals, and out the cooler line. Therefore that would remove fluid from the pan, and since there is nothing putting fluid back in the pan, it could not refill to the 3 quart capacity.

 

[BrianL]

Quote:

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With the method that I, unDummy, and sky jumper (this is who my "we" remark was referring to) are suggesting, would be that it would pump out 1-2 quarts out of the pan, to the internals, and out the cooler line. Therefore that would remove fluid from the pan, and since there is nothing putting fluid back in the pan, it could not refill to the 3 quart capacity.

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I see. However that's not what unDummy was saying, at least with mine. I think he said traditionally it would. But from what he's actually saying with mine, the 'reverse flow' theory is actually (at least partially) correct, in that it is pumping fluid from the pan to the cooler, then back to the transmission, in the top, where it's also is probably cooling/lubing "bearings, bushings, planetaries, output shaft" (in unDummy's words), before going to the pan, or wherever and then the pan. So while that's only one of the flow patterns, it is a pattern, and reversed from how most other auto transmission fluid systems work(?), *or* at least from what many people seem to think (going by their posts about how to flush the old fluid out). Then, as he says, there's also another completely separate flow of fluid from the pan up to the VB and TC.

Also, if it does have separate flow patterns, then this would probably happen too (since there would be at least 3 qts in the VB and TC to fill the pan back up):

Quote:

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No, if the fluid were to have the "reverse" flow, then the pan would fill up from fluid from the transmission internals. So you'd pull 1-2 quarts from the pan, but then that same amount of fluid would flow to the pan and fill it back up. So you'd get 3 quarts via a plug. This is ONLY with the method you are thinking is happening (I'm not saying it is not happening, just not very sure that is)

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[BrianL]

If I'm going to just drain and fill the pan a few times, will I get a pretty good mix of the new fluid with the old by just running the engine for a couple minutes in between, shifting through the gears and giving it a little gas? Or do I need to drive it?

 

[sky jumper]

Quote:

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However that's not what unDummy was saying...from what he's actually saying with mine, the 'reverse flow' theory is actually (at least partially) correct, in that it is pumping fluid from the pan to the cooler

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no that's not what unDummy is saying. read his posts carefully. he said:
- all fluid is pumped from the pan (true)
- fluid is hottest coming out of the TC, and typically goes from TC to cooler to pan
-in your case it appears to do some extra lube/cooling at the back of the transmission before returning to the pan
- some ATF does return to the pan without passing through the cooler (that is news to me).

but nowhere did he say the pump draws from the pan straight to the cooler. if you look at how a transmission is constructed you'd see that just can't be the case - there is only one "draw point" dipping into the pan - it is the strainer, and it leads directly into the VB and on to the rest of the internals.

if it makes you feel any better you can look at my used oil analysis for my nissan AT here

the column dated 9/15/05 is 9.6k mi after a single dealer drain fill (which drains about 4.5qts in my transmission)

the column dated 6/10/06 is 8.8k mi after a 5qt pan drop followed by a 5qt cooler line flush (total capacity is 10qts). the fluid I pumped out the cooler line looked cleaner than yours does, but if it had been the fresh pan fluid I just put in there is no way the latest UOA would've been so clean (all that other old fluid still in there would've showed up in the lab report).

if you still don't trust the cooler flush method then just do 4 or 5 drain fills with a few miles of driving in between (go through all gears). it will accomplish the same thing but in my opinion will waste more fluid.

 

[Steelhead]

BrianL,
the main reason your ATF discolors is worn off friction material from the bands and friction discs....this is the darkening that is acceptable and is expected....

ATF darkening and thickening from oxidation/overheating is not good and is death (usually quick) for a transmission

 

[KBFXDLI]

I would drain it with the plug and refill 1/2 and be done with it for 10k then do it again. I have been doing that on my daughters Honda crv. change out 3 qts every 10k. cheaper and the trans will not have a porblem. Plus it doesn't introduce too much new detergent into an old trans. On my new yukon with no drain plug I'll use a oil siphon down the dipstick and add 2-3 qts every 10k and drop the pan and change the filter at 50k like the book says. I have done this for years and never has a trans failure.