AT drain and refill...percentages?

kannibul

I have a Honda Civic, and it has a 12 quart system.

I drained and refilled 3 quarts of ATF today.

I plan on doing another drain and refill next weekend since I over-filled by probably 1/2-1/3qt.


So, here goes:

Since the old fluid and the new fluid will mingle, that means I have 75% old fluid swimming in my transmission.

Now I take another 25% from that, by drain and refill.

So, I could assume that I need to do 12 - 25% - 25%?

If so, then that means I have 6.75:5.25 old:new = 56.25% old fluid?

Then if I does it once again, that'd be 12 -25% -25% -25% = 5.0625:6.9375 old:new = 42.1875% old fluid?

Am I on the right track?


Thanks!

fullmonty

I had an answer in my head for you then I saw all the numbers and I lost it. Since you have 25% new fluid in there and you drain some more out, the amount of new ATF will be relitive to the amount of ATF you just drained. So I guess what I'm trying to say is if you had 10% New ATF and 90% old ATF and you drained half of it, you would have 5% New ATF and 45% Old ATF. I don't think I answered your question though. Why didn't you just drain it all and refill at the same time?

kannibul

You can't. The pan only holds 3 quarts, just as most automatic transmissions.

The only way to get it all out, is to flush it, which is a bad thing with newer transmissions as it forces fluid through the transmission in ways it's not supposed to flow.

schrack150

just overfill it long enough and it will all be fresh
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