Biodiesel at 50% when it is in the 30's will not particularly want to start, and won't run very well until it gets warmed up. I'd drop the % down for the winter.
Does your pump leak? Check for air bubbles in the clear line before the injection pump. Is the fuel filter fairly new?Andrew
I can see how crazy these cars would make people if they didn't know how to work on them and had to take it to a shop each time.