Wait until you have a quarter tank but don't push this any further. Doing this can extend your gas because you are hauling a lighter fuel load. It also gives you the opportunity to buy more gas if you run across a bargain. However, in cold weather, you run an increased risk of condensation in the fuel tank. Running a car with less than a quarter tank can shorten the life of the electric fuel pump and running on empty will often destroy the pump.
Fill up your car or truck in the morning
Morning is when the temperature is still cool. Remember that all service stations have their storage tanks buried below ground; and the colder the ground, the denser the gasoline. When it gets warmer gasoline expands, so if you’re filling up in the afternoon or in the evening, what should be a gallon is not exactly a gallon. In the petroleum business, the specific gravity and temperature of the fuel (gasoline, diesel, jet fuel, ethanol and other petroleum products) are significant. Every truckload that we load is temperature-compensated so that the indicated gallonage is actually the amount pumped. A one-degree rise in temperature is a big deal for businesses, but service stations don’t have temperature compensation at their pumps.