The problem with biodiesel isn't biodiesel itself.
If you manufacture, refine and filter biodiesel properly, so that there are no fatty residues to accumulate on the inner walls of the hosing (like clogged arteries in your own body - same deal here!) there is little to fear from biodiesel.
Half the problem is the creation of biodiesel from used cooking oil and not filtering it properly. This crap fuel is going to clog up filters, injectors and the pump. It's going to leave residue in your tank, in your fuel lines and in the return lines as well.
If you DO blow your filter/injectors/pump because of fatty deposits in biodiesel, make sure you also replace (or thoroughly clean) all of the fuel lines and the fuel tank as well.
Biodiesel is supposed to meet a certain level of refining, but there's a lot of mobs out there grabbing used cooking oil from the local fish and chip shop, running it through some test tubes in their garage and pumping it out as "biodiesel".
It's something I'd be vary careful about. The fine tolerances in the pump and injectors won't enjoy a nice lining of vegetable (or animal) fat. Remember, fish and chip shops also cook snags in their oil, and they're full of animal fats. This may pass through less sophisticated filtering systems.
As the Nissan service department and the salesman told me:
"If you absolutely HAVE to use biodiesel, use up to 20% mix, but go back to dinosaur as soon as you can".
Amen to that.
