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Message: [QUOTE="MikeT, post: 1474341, member: 21398"] OK, I know there is some sort of formula for what I am going here but I don't know what it is. I am going this the hard way and I'm sure there is a formula for it. I would like for you to help me and see if you can tell me what the formula is. Here is the problem. My van has 12 quarts of transmission fluid in it but when you drain it, only 3 quarts come out. Then I fill it with 3 new quarts of fluid, I now have 25% new fluid in my transmission. [U]2nd change[/U] If I circulate all the fluid around (mix it) and then do the same 3 quart change each quart I am pulling out has 1/4 new fluid and 3/4 old fluid. When I add the new 3 quarts in I now have 5-1/4 quarts of new fluid in the system and still have 6-3/4 quarts of old fluid in there. That means I have 43.75% new fluid in my system. [U]3rd change[/U] If I mix it again and do the same change, I have 57.75% new fluid in the system. I know doing it this way I will never make 100% but the reason I do it this way is the dealer wants $380 to change it and with 2 changes it only cost me $48 and I have 43.75% new fluid. So lets say I changed it 5 times. What is the formula that would tell me how much new fluid I have in it percentage wise? I know that 5 changes, I've purchased 15 quarts of fluid which is about $120 and with each change I have a diminishing return on my "change investment". Who can figure this out?? [/QUOTE]