I filled up my tank all the way, drove 248 miles and then filled it up again, and it took 14 gallons and i have a 17 gallon tank, i did the math and it only added up to 17 mpg, then again i filled it up all the way, drove 40 miles filled it up again and it too 2 gallons adding up to 20 mpg, whats up with my car??? its a 95 accord ex 5 speed....