AT drain and refill...percentages?
 

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!

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?

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.

just overfill it long enough and it will all be fresh
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