How to save fuel?
Refuel your car early in the morning, when the temperature of the earth is colder.
All gas stations have their tanks buried in the ground. The earth being colder, the density of gasoline or diesel is less. On the other hand, during the day, the ground warms up, so the fuels dilate. If you fill up in the afternoon or evening, your liter does not equate to an exact liter.
In the petroleum industry, specific gravity (density) and temperature play a very important role.