david,

I use my used engine oil for fuel in concentrations up to ~10% with no noticable smoke. At the price of Diesel fuel, the used engine oil is worth $2.50 a gallon.

If you take it to a waste oil collection center, its probably burned in a ship Diesel or power plant so any toxins go into the air anyway.

With the sulphur content of Diesel fuel getting lower and lower, the used engine oil in the fuel helps lubricate the IP.

P E H