Rep Power: 0

Hello
I get that there's lots of posts regarding this. But none are quite what is happening to me.
So I bought a 2003 dx civic. Sedan, automatic. 131k miles. I needed better mileage. Mileage and reliability are the only reasons this car was purchased. When I bought the car it had a code p1753. I replaced the ttc solenoid and cleared the code. Now it shifts great. All 4 gears go smooth.
​​​​​​I now have no check engine lights, the car ran and drove smooth. No smoke or noises. I drove to work this morning, about 30 miles, and it took a quarter tank. Based on a 13 gallon tank that's like 10mpg.
My drive to work is all highway. Granted I drive 75-80, but I aughta get better than that.
I do have new oil and plugs for it and I read about cleaning the ocv and maybe replacing the primary o2 sensor.
I could also subscribe to my gas gauge being wrong, but that seems unlikely since I watched it move down while I drove.
I have read about others mileage dropping to mid twenties. But 10mpg concerns me. And since there's no cel or noises idk what to do about it

 
Rep Power: 222

Check for dragging brakes, drive a couple full tanks and see what the mileage is. That fuel gauge moves quick in some spots compared to others

 
Rep Power: 0

Really? Huh. Well OK. Will do then
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Rep Power: 366

i would replace o2 sensor next if it is unknown how long.
air filter? You might find a rat's nest there (no joke)

 
Rep Power: 223

Using the actual fuel gauge to calculate mpg is not accurate. Next time you fill up let the pump click off when it's full, then reset the trip A/B. Next time you refill let the pump click off again. Take your trip A/B and divide by the amount of fuel you just put in.

 
Rep Power: 125

Almost no fuel gauges are linear so that’s not a good measure - especially these cars. You drive 100 miles and it wouldn’t move at all then suddenly you’re at almost half a tank. Didn’t stop me from getting 300+ miles per tank.

 
Rep Power: 222

this is the correct way to do it