We’re keen on some of the new clean diesel technology that’s making its way into the United States: great performance, great fuel efficiency, and the cleanest diesel emissions ever. What we’re not keen on is what is happening with new diesels and biodiesel compatibility. More accurately, biodiesel incompatibility.

Volkswagen TDIs used to be the best choice for those wanting to cut their emissions with biodiesel. After VW took a break with diesels for the 2007 due to changing EPA rules, they came back with a shocker: biodiesel beyond B5 is a no-go.

Sure, the new “Clean Diesel” Volkswagens have much cleaner diesel emissions than their previous generation counterparts. But why would Volkswagen shy away from cutting emissions even more by keeping their TDIs as biodiesel-compatible as possible?

One of our experts, Tony Cutler, here at the Green Car Company pointed out that, “The newer 2008+ diesels use a process called late post-injection. This process involves injecting a small amount of fuel into the engine post-combustion. With regular petrol diesel this isn’t an issue, because it has a lower flashpoint than Biodiesel. A higher flashpoint however, means a little bit of Biodiesel may still be left leading to oil dilution.” There is an in-depth technological explanation why biodiesel above B5 is not good for the new TDI engine, but it’s shocking that VW would settle on a technology that limits the consumer’s ability to be as Green as possible.

Tony added, “If Volkswagen implemented a process called “exhaust stream” injection, rather than using late post-injection it would accomplish the same goal (reducing emissions) but would also allow for the use of Biodiesel without the damaging effects.”

Back on the Volkswagen website, they have a fancy page with a carbon offset counter on it. If they had the foresight to keep biodiesel running in their engines, then perhaps their offset counter wouldn’t seem like a bad joke.

Ultimately, if you want to run biodiesel, don’t buy a new VW TDI. In fact, don’t buy any of the new diesels that are out now, which all seem to rely on the same technology. Find yourself a 2006 or older TDI because the “2009 Green Car of the Year” doesn’t seem to be as green as it should be.

Most importantly, take a few moments to visit www.SaveBiodiesel.org to learn more about the issue and to sign their petition.

Auto manufacturers are gearing up to get more diesels on American roads, but if they’re going to restrict our ability to use the biodiesel we want, then perhaps they shouldn’t waste our time.