Reply #11: Another note about #1 [View All]

In general, any piping or other equipment buried below ground must be below the "freeze line", i.e., a depth where the freezing point of water is never reached. For one, this prevents water from freezing inside pipes, which very easily can blow them out; you can make an "ice grenade" using this principle. Two, once below the freeze line, the temperature tends to stay fairly constant, which reduces stress on metal components constantly expanding and contracting. Above-ground piping is usually insulated or heat-traced to avoid this very problem.

In short, there should not be a significant difference in density because of temperature differences in underground tanks. There will, however, be fewer vapors when you fuel up at lower temperatures, since vapor pressure (how much evaporates) decreases with temperature.