[elhigh]

I've seen lots of mileage claims dip a bit when drivers switch from petrodiesel to bio. Then, as often as not, they state that their mileage "comes back." I think that could be attributed, first, to the lower energy density of biodiesel as a couple of other commentators have noted, but the much higher lubricity of bio frees up some wasted horsepower by slowly dissolving deposits in the engine and keeping all the bits moving more freely.

I don't have a diesel - I wish - but I have read a few pages where the shadetree mechanic would clean parts by soaking them in diesel, and soak the really TOUGH parts, or the seized engine, in biodiesel. Just drop it in and leave it. Come back in October, it'll be loose.