Since I've had my FX45, the gas gauage has stayed right around 14.1 MPG. I took a 3 hour round trip highway ride and checked but didn't reset the MPG meter after the trip and it rose up to 14.3 MPG. A couple of days later I went to the dealership for my first oil and filter change. I had them put in Mobil 1 synthetic oil. A couple days later after mostly more city driving my MPG reading had reached 14.5. Thought I'd share.