240d Runs Fine On Used Motor Oil

I have been fascinated with the idea of running my diesel on other alternate fuels besides that of Diesel which is now capping out at $1.69 per gallon. I work at an automotive dealership and have more than ample supply of used motor oil. I picked up a nice 240D with 74000 miles and have been increasing the amount of used motor oil to my mixture of diesel. Im currently running about 60% oil to diesel and while I dont really see why, it seems to run with a little more power the more oil i add. There has been no increase in smoke at all. It seems to fire off and go to a smooth idle a lot faster in cold weather. The coldest i have cranked in is 17 degrees. I make a 70 mile round trip daily to and from work is why i bought the car...might as well wear out an older car than a newer car... The $500 price tag wasnt that bad either, so being that I got it cheap, I feel justified in experimenting with it. What I would like to know is there anyone else out there supplementing fuel with used motor oil...if so what kind of ratios have you achieved? This summer I am going to try 100% used motor oil and see what happens. Comments?