I have been tracking my mileage precisely from Dec 2012-June 2013. My driving is a mix of street and highway and I burn about a tank a month (2696 miles over 6 months). Over the past 6 months my average mileage has been 21.5 mpg (stdev 0.9) running B20 from Pearson fuels (New Leaf brand biodiesel) in San Diego. My Mercedez-Benz is a 1983 300CD with everything original (I have all service records the car was purchased new) and just over 300,000 milies on the odometer. Any ideas on how to improve my gas mileage would be appreciated! The first thing I will try is a Lubri Moly purge and see if I see a difference!