Is it true that if you fill your gas tank you'll have better Mileage?

Question

Why is that, first of all is that a Fact or Myth. I think that it just ads extra Weight to your car as is carrying all that extra fuel all over the city.

Answer 1

it all depends on how you look at it.

to answer your question, you get better mileage when you have less fuel in your tank due to having less weight.

but you may save money by actually filling your tank completely and going to the gas station fewer times (depending on how far you drive to fill up)

Answer 2

Extra weight=less economy so only putting half a tank in at a time could theoretically save fuel over the long run. A gallon of gas weighs around 6 pounds so by filling the tank only halfway, you may save 40-60 pounds in weight....not a whole lot to be really significant savings. The purpose of a large tank is for range on trips....not needed for local driving if gas stations are easily available. Better to pump gas in the morning or at night when it's cooler and more dense also.

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Answer 3

To answer your question, it's a myth.  Mileage doesn't vary significantly based on the weight of fuel.  A full tank represents less than 5% of total vehicle weight.  A half tank difference is like leaving your third grade child at home.

Paul H, I agree with everything you said except the morning/evening statement.  I manage fuel inventories across the US and my underground tanks don't vary more than a couple of tenths of a degree on any given day.  You're going to lose far more to evaporation in your car's tank than you're losing to temperature fluctuations at the station.

The temperature underground is remarkably stable.  The fuel takes about 5 seconds to go from the tank, through the pump and into your vehicle.  There is simply not enough time for the temperature to change before it's in your tank.  There are pumps which can adjust for the temperature difference, but the replacement cost is about $5000 per pump.  Who do you think is going to pay that?  You and me, every time we fill up.  That cost will be added to the station's costs and will be passed along to the consumer.

Fuel pumps are calibrated to deliver 60 degree F gasoline.  If the gas is colder, you get more gasoline, because it's more dense.  In the summer, you get less, because it's less dense.  Over the course of a year, what you gain in the winter, you lose in the summer.  I work in the fuel industry and will honestly say, it's not worth my time to "schedule" my fill-ups.  Certainly not enough to make me want to foot the bill for new pumps.

Some media folks have perpetuated this myth without understanding basic chemistry and physics.  The coefficient of change due to temperature on gasoline is so small that over the course of a year, you're likely to save about $25 if you can manage to buy fuel when it's below 60 degrees F.  If over  the course of a year, the tank temps vary between 50 and 70, as they do in most northern climes, you've got a zero sum game.

If you live in a consistently high temp area, where the storage tanks are above 60 year round (Hawaii, Florida, south Texas, southern California), you could argue you're getting screwed over the course of a year.  If your winter temps consistently get into the low 40's, and approach freezing overnight, you're getting good swing on temps and aren't losing anything.  My tanks in Chicago are actually still around 50, so those folks are getting a deal right now.  The temps in San Diego are in the low to mid 60's, so insignificant in terms of volume variation.  

A 15 degree change in temp will result in a 1% change in gasoline volume.  I rarely see my tank temps outside of 45-75, so if you buy 20 gallons at either extreme, you're going to have a variance of .2 gallons, or less than a quart (0.25 ).  This is at the extremes, mind you.  Halfway to either extreme means a difference of . 1 gals, or 1.5 cups (12 ounces).  In my car with a 14 gallon tank, that would get me 2 miles under ideal conditions.  Just not enough to worry about.

Answer 4

no but you'll be better able to keep track of it...

for best mileage, drive with traffic, keep up with the slow lane and don't cause a blockage.  you'll get good mileage following traffic, you let off alot.  the biggest thing you can do is your driving style, you get twice the mileage slowing down and triple going down hill, so the sooner you let off the gas the better you will do. anticipate stop signs and lights, left off the gas as soon as you can..

   Always use your od, if you don't have one, put on 2 size larger tires on the drive wheels and remember to figure a correction for mileage.  you can check it against a gps to find it..

it really helps if you have a car with a mileage computer so you can watch it...

Answer 5

I think it does.   I know when I fill up my tank I seem to get better gas mileage.  don't understand why but it seems t happen.