This question is really part of the previous question on the advantages of biodiesel. It would have been easier to discuss the two subjects at once. However... Biodiesel does have some drawbacks. None of these pose any serious impediment to a greatly expanded use of biodiesel, with one possible exception. Biodiesel is burned to produce power and the combustion process will always produce a certain level of noxious emissions. The ideal fuel source would have no harmful emissions. Biodiesel has a lower cloud point than conventional diesel fuels. One problem that all diesel fuels share is a tendency to cloud and gel at low temperatures. This is prevented through the use of fuel additives during the winter in cold climate regions (e.g., Canada). Biodiesel’s lower cloud point makes it somewhat inferior to conventional diesel fuels in this regard, but problems can be avoided by using a lower blend ratio (e.g., B5 instead of B20) and/or fuel additives. This problem affects any fuel stored in a vehicle’s fuel tank, as well as commercial and industrial storage facilities. This has no impact on diesel engines in service in environments where the temperature does not fall below the freezing point. Biodiesel has a higher solvent action than conventional diesel fuels at medium and high blend ratios (B6 to B100). This can have a negative impact on fuel filters and fuel system components, unless they are designed for use with biodiesel. Engines that are not designed to use biodiesel may experience a higher than normal rate of failure in the fuel system, which may not be covered under the vehicle’s warranty. Information on this issue from the manufacturers viewpoint should be available on the Engine Manufacturers Association website at http://www.enginemanufacturers.org/ . These problems can be avoided through changes in the design of and the materials used in fuel systems. Biodiesel’s greatest problem lies in the agricultural limitations of very large-scale use of it as a source of fuel. Although it is a renewable resource, large-scale production of biodiesel will require correspondingly large tracts of land and industrial agricultural methods for maximum efficiency. The use of marginal lands for agriculture has been found harmful to the environment in the long term. Heavy irrigation can easily damage lands through salinization, which reduces its ability to produce foodstuffs. The lands may require heavy applications of fertilizers and other chemicals to offset this damage. The world needs to maintain its existing stock of high-quality agricultural lands and reduce the costly and damaging use of marginal terrain. The loss of quality arable lands to housing and industry needs to be limited. Marginal lands should be used for housing and industrial use, with the agricultural lands placed under protection for food production. Diversion of quality arable land away from food production to vegetable oil production could lead to more severe food shortages, if not properly managed. Since we are unable to manage out land or food distribution at the present, the adoption of biodiesel in a significant way must be carefully controlled.

• Burning B100 (100% biodiesel) may release excess nitrogen oxides. • Certain metals may oxidize in contact with biodiesel, creating sediments and fuel system problems. It can also affect some plastic types and paint. • Currently, overall costs related to biodiesel are prohibitive. http://www.futurecars.com/futurefuels/biodiesel.html

You still have to burn it, produce it, burn it etc.... All electrics are the way to go. Then as electricity is produced in renewable ways and storage becomes more earth friendly the core of the all electric can run with all these improvements without burning anything.