A few months I totaled our 300DT. Like any good Mercedes guy, I take the joke of a settlement the insurance gave me for my car and get another 123 (this time a wagon). Since the price per galloon at the time was pretty close, I started running it on biodiesel. Now, I checked here and the opinions on the biodiesel seemed pretty varied. The car idles better, starts easier, and certainly smells better with the biodiesel. However, when the temp dipped below 25, it turned to soy jelly in my tank. I put in a few gallons of dino-diesel and got it started and has been fine ever since. Replaced the fuel filters and removed the fuel tank sensor and cleaned it (talk about a well designed way to access this thing!), then it's all back to normal. Dino-diesel's price dropped so I started running it on that again. The car smokes more, idles rougher and louder, and takes a few more turns to fire up. I've read and been told bio-fuel is supposed to be lower octane, so why is it running better? I'm back on B100 full time, now.
On a slightly different note, one of the best things about the biodiesel is telling hybrid drivers I'm using less petroleum than them. Sure fuel costs more but I paid $18,000 less than they did for the car, so I got a long way to go before I'm paying more than them to drive.