A good friend is traveling the US in a diesel RV with a Mercedes engine.  He says his manual states he is not supposed to use bio diesel. 

I've never heard of that before.  I know lots of people like to blame ethanol for their failure to properly build vehicles, yard tools and mechanics that can't figure out what's wrong.  But I thought bio diesel was an improvement over regular diesel.

Do any of you have vehicles that state you're not to use bio diesel?  (we all know not to use any kind of diesel in flex fuel vehicles)