A buddy of mine who has a new f250 was at the dealership yesterday talking to one of the mechanics and he was saying a lot of the guys there take the old transmission fluid that come out of the vehicles they work on, save it, run it through some sort of screener, and for every 20 gal. of trans. fluid they add 5 gal. of diesel and run it in their old powerstrokes. Sounds kinda crazy to me, anyone ever hear such a thing?!?

It is crazy! That's an old wives tale. They used to do that in the old days, we certainly do not need it with the technology that goes into these modern power plants. I'd never put anything like that in my truck.

A buddy of mine who has a new f250 was at the dealership yesterday talking to one of the mechanics and he was saying a lot of the guys there take the old transmission fluid that come out of the vehicles they work on, save it, run it through some sort of screener, and for every 20 gal. of trans. fluid they add 5 gal. of diesel and run it in their old powerstrokes. Sounds kinda crazy to me, anyone ever hear such a thing?!?

Dexron (not F type or Mercon) or what ever was used for years as a diesel cetane improver/injection cleaner. I can vouch for the fact that it can help. I was strongly cautioned to not use more than 1 qt Dexron per tank and not more than that period. I sure as anything would not use it for anything I cared about especially at the ratio you're referencing.

That's just plane NUTS! using drained trannie fluid in your tank! I work at a major rebuilding center and you wouldn't believe all the stuff in used fluid (even cloudy red fluid) there is, not to mention friction material, copper and steel...DON"T EVEN CONSIDER IT!

Use it for chain lube in your chain saw.

FWIW, my 2006 Duramax Diesel Engine booklet says on p. 5.2, Diesel fuel that has been mixed with engine oil or automatic transmission fluid could damage your engine and emission controls. They'd probably say even worse about used oil or ATF.