At 315K in Santa Cruz, CA my wonderful 240D was pulling 22-25mpg around town and 28-33 highway. When I added 1 part clean canola oil to each 4 parts diesel into the fuel tank, mileage went down a tiny bit, and behind me smelled like a heavenly Hawaiian barbeque, 'cause that's where the oil was from. Ran clean, a little less power on steep hills...needed the tank cleaned out after about 20,000 miles, tho...
Car was totalled in 2008 when a teen pulled out right in front of me...but engine was still running w/radiator wrapped around front of engine. What a beast!