Originally posted by AirKnight:
Drain and fill is one of the best way to dump money and not do a good job. It'll take way too much fluid to complete change the fluid in the tranny using the drain and fill method. I opt for a complete machine flush, or at least a ghetto flush. A proper flush can get 99% of the fluid while a drain and fill can only change 70% of it.

AirKnight is correct here ... think about it for 2 minutes and it will all fall into place. Just for easy math, let's assume the car's tranny takes 12 quarts of fluid. To make things round out, let's assume that when you "drain" the transmission, you can only drain and subsiquently refill only 4 quarts at a time. Now, let's assume that your fuild is 100% burnt and definitely in need of a draining/flushing. Using the drain/run/refill/repeat method would work as follows:

100% burnt fluid, 1/3 of which is removed and diluted with 100% pure fluid. This leaves roughly 67% burnt fluid. Now, if all the old fluid stayed sperated from the new, this method would work and you would have 100% new fluid in after 3 drain/refill routines. However, when you run your car, you are turning the Torque Converter, which is doing a pretty good job of mixing the new with the old.

So, second drain and refill result in NOT draining 100% burn fuild, but diluted 67% burnt fluid ... so on and so forth. You will NEVER exchange 100% of the burnt fluid with this method, NEVER. You will merely be diluting the mix. Kind of like how we used to do in high-school with the parents liquor collection

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