If the thermostat is stuck open the engine will be running cold and the
mixture will be way too rich. Do you have good heat out of the heater?

That's about right for combined city/some highway driving. These cars are no
screaming gas misers, especially around town in stop start traffic.

It depends on how you are determining MPG.

Factors effecting fuel efficiency are: how much weight the car is carrying,
weather, altitude, how the car is driven,(driving 65 mph instead 50 mph uses
35% more fuel),  tire pressures, kind of tires etc.
It was just proven that the gas claims on the EPA stickers placed on new
cars are a bunch of hogwash and they do not get close in the real world..
It looks that you have spent a lot of money to replace perfectly OK parts.
Want to save gas? drive slower.

Are there any owners of a 2000 Focus with the SOHC Engine that has
experienced gas mileage that doesn't come close to the original. I believe
the original MPG was 25 city 33 highway. (Correct me if I am wrong).
Mine is only getting about 20 to 22 average. I've had the fuel pump changed
under recall, changed the fuel filter, changed the plugs and wires 3 times
in the last year, changed the O2 sensor twice in the past year, installed a
ford replacement ignition coil and throttle body position sensor, installed
a K & N Air Filter, and still no change in the mileage.

Anyone else having mileage problems or have any suggestions.

Thanks

I'd have to say you have something going on somewhere. I have an 04 ZX3 with
the 2.3L PZEV engine and im getting about 27 combined, mid 30's highway,
your smaller engine should give better results. Some things to look at:

Have you tried some fuel injector cleaner ? If not, try 2 bottles together
now, than 1 more with the next 2 or 3 refills.
Are the tires inflated properly ?
Are your brakes dragging ? This is a common cause of poor milage.
Do some self evaluation...are you a lead foot driver ? Try to purposely
drive smoothly without sudden stomps on the gas pedal or brakes. Try driving
no more that 10mph over the speed limit to keep engine rpm's lower.