I'm sorry I can't help but laugh at y'all complaining about get 18mpg city. My 540i gets 14 on a good day in Charlotte and 12 in Boone. I suspect fuel filter on my end, but I'm busy with the valley pan right now so it will have to wait. I did put a bottle of techron in and noticed 2-3 mpg improvement in city and highway for about 5k miles. Your fuel filter is like 3 years old it may be worth changing, and give the techron a go.