It sounds strange, but I have a friend that has been adding small amounts of transmission oil/fluid to his diesel at most fill-ups. Is this a common practice or perhaps an old practice? Along w/ some Star-Tron his mpg has increased. Any comments on this? He has been suggesting it to me for several months now. Thanks for your responses.

I have done this, I think this is an "old school" practice. It is said to clean the fuel system. Trans oil is high in detergents. I have done this on my older heavy equipment. I usually fill the fuel filters w/ tranny oil when I change them.

how much we talking per tank?

Moved to Fuel Supplements section. This has been discussed several times before. In my opinion, you should stay away from the use of transmission fluids with any Duramax. They can clog your high tech fuel injectors! Stick with the actual fuel supplements that are made for diesel fuel.

I have done this, I think this is an "old school" practice. It is said to clean the fuel system. Trans oil is high in detergents. I have done this on my older heavy equipment. I usually fill the fuel filters w/ tranny oil when I change them.

I've done this too. On my mechanical injection it runs no different with a filter full of it. In the winter it's probably too thick but I don't think I ever tried it in the cold.

This has been done for years and causes no problems on a Duramax. Just add 1 quart to a fillup. Put what you feel is 1/2 tank and stop then pour the quart of transmission fluid down the filler neck and continue to fill the tank until full. It adds lubracation into the system and help keep the injector system clean. I run a quart about every 5 tanks and it does help.

I just started running 2-stroke oil. I added 32 oz at last fill up. I have noticed it seems to run smoother. I have not seen any mileage difference yet, still too soon to tell.

I know someone in oregon who collects used transmission oil from shops and filters it and does a 50/50 mix hes been doing it for years and no problems.