Lemme guess--you want to use your gas guage to figure out how many gallons you used in a certain number of miles, right? That's NOT the way to figure out fuel economy. Here we go again with how to calculate mileage:
DON'T assume that the gas guage in ANY car is accurate. For example, if the tank says "1/2", and the tank holds 20 gallons, it's WRONG to assume that the tank has 10 gallons of gas in it. Guages are SO imprecise that the actual amount in the tank may be anywhere from 8 to 12 gallons. The gas guage is a general indicator of tank status, but is NOT a precise measuring instrument. Worse yet, no two vehicles of the same make and model will have gas guages that behave the same, so owning one year and model of car will NOT allow you to apply the behavior to another.
So you want to figure out your mileage? Here is the CORRECT way:
1. Fill your tank up at the gas station all the way to the top. I mean literally ALL the way up to where you can see gas in the tank filler neck.
2. Mark down your odometer mileage of when the tank is filled as described above.
3. Drive around until you have used up a bunch of that tankfull. The closer you are to "E" when you refill, the more accurate the calculations will be.
4. Refill your tank at the gas station, and again try to get the gas level to the SAME as it was the first time: up in the filler neck. Write down the total amount of gas the pump says you put in this time.
5. Mark down your odometer mileage again.
6. Take the odometer reading from the first time you filled the tank, and subtract it from the reading at the second fill. This is the number of miles you drove between fill-ups.
7. Now take the number of miles driven between fill-ups, and divide it by the number of gallons you put in the tank on the SECOND fil-up. The result will be your miles-per-gallon.
