What are the drawbacks of using biodiesel?

Price (often higher), location, and cold weather. Biodiesel is a commodity and the price fluctuates compared to diesel. Finding a good reliable B100 retailer can sometimes be difficult. Biodiesel gels (or freezes) at a higher temperature than diesel. So in a cold climate you may find running B100 is not possible. Even in Houston we recommend biodiesel users blend with diesel October through April. In colder climates you must blend B100 with diesel to lower the overall gel point. If you burn biodiesel in an older vehicle you'll possibly produce higher Nox emissions. Biodiesel is corrosive to rubber, however modern vehicles have no rubber touching the fuel. Both diesel and biodiesel are corrosive to rubber. Biodiesel more so.