hey guys, i've never had my CEL or SES light go on, and I am getting TERRIBLE gas mileage. I can barely get 200 miles out of a tank, and I fill around 16 to 16.5 gallons each time. I know if O2 sensors go bad it can cause that, but I have no lights on my dash to signify this. What else can cause poor gas mileage? my oil is overdue, but it was like this even before that. What can i do to improve it? i'm a college student filling premium spending $65 a week on gas because of this. This is mostly highway miles also, with some, very little, spirited driving.