Cummins says 20% but Dodge says 5%. More to it than just the engine. Since we have a 2012 Dodge dually, we hope they come out with a fix for this issue. It will probably mean an addition of another filter and a programming change. Dealers know when you have been using bio diesel, because it can cause a big gel like mess in the engine that is expensive to clean up. Family member is a mechanic at a Dodge dealer in IL and they see this problem all the time because 11% or higher bio diesel is just about all you can find.