What Causes poor gas mileage in a Ford Fusion?

Answer 1

Many things including: worn spark plugs, ignition coils, burnt wiring, bad tires' worn frontend parts, wheel alignment and tire pressure. I learned this weekend that a faulty engine coolant thermostat, if stuck open, will give you poor mileage. The coolant sensor will indicate the coolant isn't heating properly and will make the computer enrich the air/fuel mixture. The way I found that mine was stuck open was: check engine light on, drop in fuel economy by 2-3 miles per gallon, and the water temp gauge was reaching operating temp slower than normal