Hyundai Sonata 2006 V6 3.3l Very poor MPG
 

I just bought a 2006 Hyundai sonata, well managed and serviced
the bad thing is the MPG is killing, the car reads 11.7MPG CITY, and 12.2MPG
Highway. Am quite dissatisfied and disappointed. Please What can be
done, Am spending a lot of money on Fuel, please I need help

Is the check engine light on? What are the codes?
Even if there is no check engine light on please have the computer scanned for codes and pending codes.

Is the engine warming up correctly? A bad thermostat could prevent proper warm up. Are you driving mostly short distances with a cold engine?

Check if the brakes are dragging.
Have a look at the spark plugs.
Check the air filter.
Check the tire pressure.
Check the wheel alignment.

With the fuel consumption this high I suspect there is more than one reason for it.

the check lights are not on, I cleaned the air filter, I changed the spark plugs.
 

I took it to a mechanic, he changed all that you suggested, the car still reads 12.1MPG in the city.
Am yet to take the car for full diagnosis.

Are you driving mostly short distances with a cold engine?

If you were driving short distances, lots of starts and stops then I can see this as normal but for me the car is amazing on the freeway. I wouldn’t take the digital MPG or how many MPG you have let on the dashboard as a accurate read. Always seems to fail me but as far as a pretty powerful v6 I really like the car and the gas mileage it puts out.

Just in case there is a problem within the system, have you considered doing your own check of miles traveled and gallons consumed?

At least you would have verified the system is accurate. Can you do this?