Ford Focus fuel economy?
 

I thought I read threads in here previously about the Ford Focus losing some fuel economy after it gets some age on it. Please refresh my memory on what was discussed, or a link to the archive that ay have this info. Problem is with a 2004 2.3litre focus. Seems to have lost approx 8mpg. Are these common to have things like the coolant temp sensor fail,or thermostat? Those are the first things that come to mind for me. Any help is appreciated.