Biodiesel is ok up to 5% (B5)as it is largely indistinguishable from D2. Beyond that you're on your own, as there are no ASTM standards for Biodiesel stability. In fact there's no agreed upon test STANDARD at all in the US for stability with Biodiesel. Caveat Emptor. European Biodiesel comes primarily from rapeseed, while ours is mostly soy based, although there is talk of building a giant refinery in Canada to refine poultry fat into biodiesel. (actually, I think NREL says the animal based Bio is more stable). The rapeseed stuff does have a (European) stability test, but the test doesn't work on the soy based stuff we get.

The B20 stories about it cleaning the gunk from the system and plugging filters are in fact true: The higher the concentration of bio, the more likely that you will have filter problems. Cummins and DCX have ok'd B20 for use in controlled fleets, where the fuel quality is closely controlled. Otherwise B5 is the limit.

Bio fuels like B5 actually have better lubricity than normal D2. The new ULSD D2 comes with a HIGHER minimum lubricity standard than the old D2 LSD. This new standard was driven by the fuel system and engine manufacturers (International, Cummins, GM, Bosch, Siemens, etc)to meet the requirements of the newer high pressure common rail fuel systems. Lubricity with the old LSD was generally ok, but there was very wide variability across the country, depending on the base stock and refinery process used to make Diesel.

Lots of our fuel has been coming from Canada and processed by Hydrocracking, which yields a very low lubricity and leads to subsequent high fuel pump failure rates. The new standards insure that a Higher minimum lubricity, although not as good as Europe, will be out there. Additives to improve lubricity are now added at the refinery and additional mouse milk additions at the pump are unnecessary with ULSD.

Energy content of the new ULSD is around 1% worse than the old LSD. Real world (controlled) fleet tests reported by the industry indicate the 1% is lost in data scatter. The energy content loss is believed to be due to the hydrocracking stripping the long chain HC molecules along with the sulfur removal. The Oil industry is working on this.

As to fuel system leaks, the problem is that the different types of rubbers in the fuel system react to the aeromatics in the fuel. All rubbers take a set or swell with exposure to fuel over time. Dramatic changes in fuel aeromatics cause problems with some seal formulations, The new fuels have different aeromatic content.

Newer engines shouldn't have problems as the seal materials have been upgraded by the manufacturers over the years, but if your engine is old, get ready to replace the seals.

A tank or two of the old LSD won't hurt the particulate filter of an o7 Diesel, but continued use will plug it and shorten the interval between ash removal service. LSD will not be available after this fall when the conversion to ULSD is complete.

Off road (red dyed) high sulfur diesel will be out there for a couple of more years, but eventually that will go away too.

Finn