I think i read somewhere that the pump which pumps fuel into the engine heats up and thus having some fuel in the tank helps cool it off. You already do amazing high mileage with your car, why not just fill it up when when you see the gas prices go down; i mean minimum half (5 or 6 Bars) at least or else you'll just be filling up about 17 litres; but it's up to you.
Be proud of your mileage (MPG) not how far you can go on one tank
