Unwashed biodiesel can have residual glycerine in it. This can glogg up in your inline fuel filtre/ water trap. If your gonna run unwashed BD, be sure to carry a spare inline filtre in your glovebox and the tools to change it. If your filtre becomes overly clogged your car will simply stop as fuel cant get through the fuel line to the injectors.
I have run unwashed BD in my Merc. and needed to change the filtre on occasion. I now only run washed BD, and havent bothered with changing filtres outside of normal servicing.