Biodiesel is a fuel that is typically made up of vegetable and animal oils mixed with an alcohol. A 100% mixture of biodiesel is called B100, the 20% blend of biodiesel (and 80% normal diesel) is B20, and the 5% mixture is B5. Most diesel vehicles on the road today have no problems running B5 (similar to how most gasoline powered cars can run E15 mixtures of 15% ethanol and 85% gasoline). With some vehicles however using B20 can cause problems (especially contaminated oil, which can lead to lubrication failure) which aren’t covered by the warranty.
Because of the unique way diesel is taxed in Illinois and the prevalence of higher mixtures of biodiesel there, many cars are certified for running on B20 only if they are licensed in that state. If you do decide to run biodiesel (especially higher percentages) in your vehicle, it’s a good idea to regularly check your oil level. If the level increases, the oil has become contaminated and should be changed.
Here is a list of B20 compatible biodiesel cars in 10 different categories.