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ATF Fluid Change Idea


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Would it be possible to unplug one of the cooler lines and put one end into a bucket while the other into the fresh ATF? I think this is how the bladder system works, but I haven't ever used/seen it. Could it be a DIY at home bladder? Thanks
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This is almost how I do flushes at home on my 3 cars that allow for it (including the Legacy).

 

Funny timing, I'm almost done tracing the cooler in and cooler out fluid circuits in the valve body. They're more complicated than we originally thought, or so it looks on the surface. Either way, you're going to run into one problem: The ATF pump does not suck through the cooler line. It pushes fluid. So your drawing is half right. Unplug one cooler line, and stick it in a catch bucket. The other portion to your design actually needs to be gravity feeding fluid into the trans dipstick fill tube, or pumping fluid via exterior pump, back into the other trans cooler line.

 

I forgot which hose to pull. The simple answer is to pull one and have your buddy turn the car on. Fluid will immediately come out of one unplugged end. There's your answer. If you're feeling extra excessive, unplug the trans cooler line return under the car near the trans, and attach a temporary hose between the hard line on the frame rail, and your bucket placed aside your open driver door. This will have your trans pumping old fluid out all the way through the cooler line, which will flush out though the radiator heat exchanger, and exterior filter by the battery. Make sense?

 

So, you turn on the engine and watch that bucket being fed by an extra length of hose. When the bucket fills a few quarts, stop the engine and fill up the trans with fresh fluid through fill tube. Repeat. Consider also flipping through PRND, with brake pedal firmly held of course. If you're going through the trouble, might as well do it all the way with a little extra energy.

 

As for how fast to expect fluid to come out,

On my old Avalon, fluid was pumped out at a slow rate which I could match pouring fluid in the dipstick, so I never had to turn off the car!

On my old Lexus LS, the trans is a whole different animal. Pumps fluid so quick you have to watch it carefully. Run engine for a very short time, while it pumps out 2 quarts, then quickly shut it down and refill trans with fresh fluid. Repeat again and again.

Not sure where the Legacy falls. The orifice for oil cooler outlet through the VB is only maybe 1/4", but at high pressure you can get a LOT of fluid through a passage that size. So I don't know.

 

Good luck.

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Would it be possible to unplug one of the cooler lines and put one end into a bucket while the other into the fresh ATF? I think this is how the bladder system works, but I haven't ever used/seen it. Could it be a DIY at home bladder? Thanks

 

No. The trans will not draw fluid back in, you'd have to fill thru the dipstick like Climber stated.

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If you could somehow seal off the bladder such that the trans pump would build pressure in the bladder by pumping in fluid, thus causing separate fresh atf to be pushed back in the return tube, then that could work. Sounds complicated. I like my way better, but would have to reconsider if I had a shop that did 5 flushes a day, every day.
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just principle check not a reality yet, but if i were to guess around 12

 

That would be what I would use. It becomes hard to tell towards the end, new mixes with old.

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Just use a drill-pump to pump fluid into the filler neck as needed. Graduate the buckets you use, and fill as fast as it drains.
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