Do you get better mpg when you fill your gas tank rather than a partial fill?

Answer 1

No, it goes the other way, but very slightly. If you carry 10 gallons less, the car will carry 60 pounds less weight. Decreasing weight does nothing to aerodynamic drag but rolling friction is exactly proportional to vehicle weight and it effects the power needed to accelerate. So it makes more difference around town than on the highway.

Our Toyota Prius displays current and average mpg and graphs it for you. 5 people (inc two kids, total = 600 pounds) versus one 180 pounder goes from 46 mpg to 49 mpg or so for the same conditions, speed, terrain.

So a 6% increase in mpg by decreasing vehicle weight by 10% has been my observation.

Leaving 60 pounds behind for a 4000 pound car should up mileage from, for instance, 20.0 mpg to 20.2 mpg. Real, but hard to measure - 0.1 gallons over 200 miles. Making twice as many stops for gas will definitely use a bit of gas - about 0.05 gallons by my estimate. Half your potential savings. Plus wasted time.

Better option: Clean out the trunk and back seat of anything you don't need.

Better yet: Leave off any roof racks when not in use, that makes a bigger difference (and it will be quieter)

-David

Answer 2

While you would save a small percentage on your mpg by having less weight from a full tank, I would have to guess that the extra stops to get gas would negate any savings.

I notice no difference in my mpg whether or not I have a 180# passenger. Five to eight gallons of fuel certainly doesn't weigh enough that you'll notice any fuel savings by running a partial tank.

Answer 3

only fill up your gas in the morning cause then the fuel is cooler which makes the volume denser, so you get more gas

Answer 4

Less because you have to carry the weight of fuel

Answer 5

No. The difference in weight would not be noticeable in most cases.

Answer 6

I really doubt you could measure the difference !