how does it work when using biodiesel. Can it be mixed with regular diesel? can you go back and forth? Just asking for my dads van, its a 2006 duramax diesel van.. There are only 2 stations here selling bio diesel and both are by usf and he cant go there every time he needs to fill up. Also, with biodiesel is there any difference in fuel economy or the way the engine runs or anything? Anything special need to be done, or not done when running biodiesel vs regular diesel?