Do you get better gas mileage if your tank is close to full, or close to empty?

Question

My mom said that your car gets better gas mileage if the tank to closer to being full. But I thought I remember hearing that you get better gas mileage when the tank is close to empty. Which one is it?

Answer 1

Logic would say that the less weight the better mileage.



There are some bad effects though from running your tank on near empty, like your fuel pump sucking up all the nasty dirt/sludge on the bottom of the tank.



Also gas gauges in the dash are not linear. meaning when you fill up your tank the gas gauge does not drop at the same rate. the gauge will drop at a steady slow pace to about the 1/2 point, then it would drop quickly to the 1/4 point then it would slow down again to the E.

Answer 2

I can't imagine how a car would be more efficient with a full tank. The only variable I can think of (especially with electric gas pumps) is weight. So the car should be more fuel efficient as the tank empties and the car gets lighter.



But, like the other guy said, the difference would be so negligible I doubt you'd ever notice the difference. City vs highway driving, hard or "rabbit" starts and gas mixtures based on the time of year in certain areas of the country would have much more affect on the gas mileage.

Answer 3

Your car will get the same gas mileage if your tank is full or almost empty. The weight of a full tank which a 20 gallon tank it would weight about 100 pounds weight of the full tank doesn't make a differance. Its just like if you have someone riding in the back seat. THE GAS MILEAGE STAYS THE SAME.

Answer 4

I would think it would be better being on the full end rather than the lesser of the two. I believe it depends moreso on the type of car you're driving and how well maintained it is on general maintenance of the vehicle.



For the best gas mileage, car pool with someone else that's going to same destination. Swap out from time to time so, that you both would be benefitting from the carpooling as well as you're saving the environment by allowing less carbons/pollutants into the air. Plus, key note here with gas prices be outrageous as they are carpooling is a good idea!



Hope this helped sorry I couldn't give you a more scientific or more mechanic point of view as the others have done so.



good luck

Answer 5

I believe you will get slightly better gas mileage if you have less gas because less gas = less weight on the vehicle, but its not good to always run your gas on empty, its better for your engine to keep your tank always a quarter tank at least or higher. Especially with Engines with fuel injections when the gas is on empty really bad to the point where you only have about a liter of gas your fuel injection hose gets filled with air instead of gas. So In theory yes less gas makes you lighter and could get you 1 or 2 mpg more but its not worth it. Weight is the reason a 6 cylinder sedan gets 21, 22 mpg and a 6 cylinder SUV gets 14 mpg, the SUV weighs alot more then sedans and takes ample power to move a heavier vehicle.

Answer 6

I would say closer to full for two reasons.

1-More fuel, less evaporation.

2-The more gas you have in the tank, the cooler the temperature, the more vapor you have in the tank, the higher the temp. The cooler the temp the more efficiently the gas burns.

Answer 7

When your tank is full, it is almost always more gas efficient.



However it is difficult to measure because the difference in efficiency when your tank is full vs. empty is so small, its negligible.