In the 4 years I've owned my wagon the best milage I have gotten is 28 mpg. I pretty regularly get between 24-26mpg. I wouldn't expect the 300 sedans to do a whole lot better, maybe a mile or two better. The 240 manuals get the best, followed by the 240 autos. 20 mpg is too low. Some things to check would be:

1. Valve adjustment
2. Air filter
3. Tire pressure
4. Dragging brakes/Dragging e-brake
5. Fuel filters

__________________