On the temperature part... the volumetric coefficient of thermal expansion for gasoline is about 1 part per thousand per degree Celsius (950*10^-6 for the nerds among us).
So... a 20 degree Fahrenheit change in ground temperature is about 11 degrees Celsius. And 11 parts per thousand on $3 gasoline saves you about 3.3 cents per gallon. That’s not a major savings but its not zero either.
3 * (989 / 1 000) = 2.96700
I would like to know where in the USA there is going to be a 20 degree change in underground fuel storage tanks from morning to afternoon!!! BOGUS!!! Or even from month to month!
Ground temperatures at the average burial depth of a gasoline tank doesn't vary 20° in many parts of the country from summer to winter. Not at all from morning to afternoon.