I have run a few gallons of BioDiesel, both straight and as a mix with PetroDiesel. Seems to work fine except it solidifies in the winter. 20% biodiesel seems to be OK at 20 deg F so far. 40% is marginal and 60% & 80% are also frozen solid. (I have some sample mixtures in bottles on the back porch to check it out.)
I'm sure the technology exists, with additives and/or processes, to render biodiesel which works as well or better than fossil diesel in the cold.... we'll work it out!