Why does my honda civic give me bad gas mielage?

Ok I won't hide anything. Hopefully someone solves the problem. I bought my 2009 honda civic ex salvage. Was hit on the left side. Cosmetically looks good. Checked the engine and it's good. Anyways there's a sound on the right. A lot of people are telling me it's the motor mount. Common in civic this year. I had another civic and it had the same problem. Anyways the most I get is 180. I don't drive on the freeway. I work close by. But these cars are 25 mpg city with a 10 gallon. Anyways would changing the motor mount give me better gas mielage. I already changed the oil. Haven't changed the spark plugs but if anyone suggests checking anything let me know.

Mileage figures from makers are with:
Closed track, not stopping or starting.
Really hard tires.
Not over 35 mph ever.
Dry smooth pavement.
No high winds, fresh wax job.
Tuned up like you would not believe.
Minimum amount of gas in tank, no extra fluids under the hood.
No extra weight inside, skinny woman driver, some say they remove all but one seat, empty trunk and glove compartment, but have not verified those.
That is for highway miles. Not sure about the city driving standards, but not any more realistic compared to actual conditions.
You might not have filled up the tank to 10 gallons.

Bad motor mounts have no effect on fuel economy. You could do a lot; have the tires at the right pressure, put in new spark plugs, have the wheels aligned pull the OBD2 codes and give attention to issues related to any trouble codes that come up, drive more conservatively.

It is a older car and it is only rated at 26 city and 34 highway. So if your getting 25 mpg in the city that is actually pretty decent.

you can make sure the air filter is clean and put in new spark plugs. You might also get the fuel injectors cleaned by a professional shop. But i do not think it will make a huge difference as it is an older car with a 5 speed torque converted automatic.

Also, make sure you have good quality tires and make sure they are properly inflated. Motor mounts should not affect gas mileage.

Ex salvage

That alone is probably 90% of the issue.