There's little doubt that biodiesel in general is a good idea, since at some point, fossil fuels are going to be in desperately short supply. And with the breached Deepwater Horizon well still belching thousands of barrels of crude into the Gulf of Mexico daily as of this writing, petroleum is in bad odor at the moment.
Biodiesel is marketed as being the ideal eco-friendly option for any diesel-fueled automobile, since it's made from processed vegetable oil and forms little more than water vapor and carbon dioxide when it's burned. Not so bad, right? Well...
Whatever it's derived from, diesel fuel isn't the best thing ever for the environment. Sure, bio-derived diesel is renewable, unlike the fossil kind...but the problem lies with the combustion products. We're talking carbon dioxide and water vapor here, the top two gases in the greenhouse effect pantheon.
Then there's the fact that it takes a lot of energy to process it into its final form...and some of that energy is derived from dirty-burning fossil fuels. In other words, even clean, eco-friendly biodiesel may contribute to climate change. Talk about your irony!
Did you know that biodiesel can congeal if it gets cold enough? Depending on the purity, it can become a gooey, sticky mess if the temperature drops too far below zero. That's one reason why so-called B100 fuel, 100% biodiesel, isn't often sold in northern tier states.
B20 fuel is a better option; it's composed of 20% biodiesel and 80% petroleum diesel. I'd recommend that you not put anything higher than B20 into your tank -- at least until car manufacturers make it possible. That's not likely to happen, by the way.
Biodiesel is heavier than conventional diesel fuel, which makes it difficult for manufacturers to comply with recent federal emissions mandates. Rather than redesign their engines, auto manufacturers are starting to refuse to honor their engine warranties if you use anything heavier than B20
What's It All Mean, Alfie?
Biofuels are a good thing; let's be clear on that. We'll desperately need the technology before long, and it's best to have it developed right now. But there are caveats that you should be aware of; despite the optimism by environmental groups, it's far from a perfect replacement for fossil fuels.
Bottom line? Don't fall for the hype. At the moment all forms of diesel are more expensive than gasoline, and none are particularly good for the environment. It's a good idea to work your way toward using more biodiesel, but don't go whole-hog quite yet.