Is gasoline usually more dense in the morning?
According to HowStuffworks, it’s true that gasoline is denser when it’s cold , especially early in the morning when ambient temperatures are low. So there’s a solid reason behind the theory that you’ll save extra money if you refuel early in the morning. Unfortunately, however, that is not the case.
The change in the actual density of gasoline is very small and insignificant.
First of all, assuming it matters when you buy gas so does this make any difference? Yes, gasoline is sold in gallons in the United States. (Even in other parts of the world, it is sold based on volume, although the measurements are different, the same principles apply.) However, the density of gasoline changes based on its temperature. Cold liquid gasoline has a much higher density than when it is at high temperature. Thus, there is a view that a gallon of cold gasoline contains more energy than a gallon of hot gasoline.
The theories above are not wrong, but the change in the actual density of gasoline is so small that you don’t need to think about changing your schedule to fill up in the morning. Another thing is that most gas stations store fuel underground, in insulated containers. According to a study by Consumer Reports, small amounts of gas lying on the ground in pipes can warm up if given enough time. If gas circulates on a busy day at a gas station, this effect is almost negligible.
A study also by Consumer Reports found that gasoline increases in temperature from 60 degrees to 75 degrees Fahrenheit (15-21 degrees Celsius) only increased volume by 1 percent. When gas prices are reasonably low, choosing when to fill up just because gas density increases or decreases can only save you a few cents at a time. Therefore, you should not waste time thinking about when to refuel is the most economical.