Today I flushed the auto trans in the brick. Hats off to the info contained in the FAQS here on how to do it, the job set me back a hair over 20 bucks including a case of dexIII and hose and clamp from Home Depot. Now my question/thought- I flushed it today with 12 quarts and to be real anal I plan on doing it again after next engine oil change(in 1500 miles or so). My plan is to flush thru another case of dino oil and then add synthetic into the system. So as I'm doing this, pumping two quarts out and then adding two quarts of synthetic and repeating etc. Are I not just mixing the synthetic with the dino oil? I guess what I am asking is will I ever have truly synthetic oil in there or will it always be mixed using this method? My thoughts are to use one case of dino and 8 quarts of synthetic at the end. Questions like this keep me up at night, God help me..Happy New Year everyone..

Yep, I think you are being a bit anal.

Really no need to use any more non-synthetic.

If you suck up as much as you can from the pan before you start pumping, and replace it with synthetic, you will approach a 90% change. That's just fine.

And I'd probably just run a about 10 qts of AMSOIL through it.

When I get a new "used (of course)" 240, I always switch to synthetic right away (as soon as I know there's no tranny leak).

Eight qts. doesn't seem enough of a flush, to me. I run through 20 quarts (I buy two cases at a time, and keep 4 as spares) to be sure; and after about 12 quarts run through, I can see that the old fluid's color changes to the bright cherry of the new stuff.

My preference is AmsOil ATF, by the way -- but any synthetic with a reputable brand will be an improvement.

Happy New Years.

I agree, not really necessary to change it that soon, but in my opinion when you are ready to do it, flush it all out at once and go with 100% synthetic. (Mobil 1 products are my choice). Hope this lets you get some sleep.
- Bill

Correct - some intermixing will occur, and it will never be truly 100% synthetic. Such said, since you did a complete flush, it's really not necessary to switch on over in such a short period. Changing over even at 15k can be considered early, though it wouldn't hurt anything either.

-- Kane
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Blossom II -'91 745Ti/M46 ... Bubbles -'74 144GL/BW35 ... Buttercup -'86 245GL/AW70
The Wayback Machine -'64 P220/M40 ... The ParaBox -'90 745GL/AW70