It ’s true that petrol is more dense when it ’s cold , which means typically it ’s most dense in the early morning 60 minutes when it tends to be coolest outside . Thus , there ’s solid logical thinking behind the theory ( or urban legend , if you prefer ) that it make the most financial mother wit to fill up your car at the heart in the sunrise . However , unfortunately , reality does n’t diddle out that way .
First off , assuming it weigh when you bought your gas , what difference does it make ? Well , gasoline is sold by the gal in the United States . ( Even in other parts of the earthly concern , it ’s sell based on book , even though the measurement differ , so the same principles lend oneself . ) However , the denseness of petrol changes based on its temperature . Colder gas is more obtuse than warmer gas , so another means to look at it is that a cold Imperial gallon of natural gas contains more energy than a warm gallon of gas , even though they might cost the same . And that ’s why this hypothesis appeals to the budget - witting among us .
Even though the science is sound , the actual compactness alteration of petrol is so small that it ’s airy to exchange schedule just to obtain fuel super early in the morning . For one affair , most gas place lay in their fuel underground , in to a great extent insulated tanks . accord to a subject field byConsumer Reports , the modest amount of throttle that sit above background in the lines might warm up if it sit there long enough . But if the gaseous state is flowing swimmingly on a interfering sidereal day , it wo n’t matter . And even if there is a lull between customers , those few slightly - warmer Imperial gallon wo n’t sham the economic value of a whole tank .
The said Consumer Reports investigation also found that gasoline that rises in temperature from 60 degrees to 75 degrees Fahrenheit only increase in volume by 1 percent [ source : severely ] . When gas pedal prices are reasonably low , that wo n’t touch on the per - gallon price much , probably just a few cent averaged out over a full filling - up . So someone who was drive out of the direction to fill up in the former morning would probably burn off up more fuel die off course than they ’d be likely to keep open . Even though gasoline should be the most dense in the morning ( or whenever air temperatures are the coolest ) there are several other factors at work preventing this from being an efficient , cost - saving fill - up strategy .
