No Idea...
I've always lived by the rule of. "If you can afford to drive a Mercedes, why should you be concerned with fuel mileage to begin with ?" So I go by this rule with all of mine, as well as my other cars. Someone once asked me what kinda fuel mileage I get, in one of my Lamborghini Countach. My response was simply, " At two hundred miles per hour, or at one hundred miles per hour?" He just shrugged, and walked away... I was amply entertained for the afternoon, and had some laughs about it with my Fiance' while we drove around wasting gas all day, in the car. She heard his question, while she was in the car, and asked me when I got in if the guy seemed to be a bit slow or something..,"There goes Rainman". Kinda cruel we both knew that, but it was too, much to resist at the time, and we were within the sound proof confines of the car.
I know my fuel mileage in my Tractor trailer, is something like 7 miles per gallon. This is only because of taxes, and staring at the fuel gauge, and others all day for so much time. Also, to plan trips, and stops.