Above ground tanks, thermal expansion, and how it costs you money
If you are like me and are always looking for ways to save money, you may have heard that thermal expansion in above ground tanks at gas stations might be costing you money. Is it enough to worry about? Maybe. They also might be saving you money. In this article we look at what above ground tanks are, how they work, and you can calculate whether they are saving you money or costing you money.
When you go to a gas station, look around and see if you see any big tanks that look like they are full of gasoline like the picture above. Most gas stations keep their tanks underground, where you can’t see them. Occasionally though, you will see gas stations that keep their tanks above ground. They keep them above ground to save themselves the cost of digging a big enough hole to bury them and to prevent the types of environmental problems that a tank underground can cause if it leaks.
Why above ground tanks could save or cost you money?
The difference between underground tanks and above ground tanks is their temperature. Underground tanks will be the temperature of the ground they are buried in. At the latitude I live in, that is about 55 degrees Fahrenheit throughout the year. However, if tanks are above ground the gas inside them is likely to be the same temperature as the air around them. Where I live this could be below zero in the winter, or 110 degrees on the hottest day of summer.
Do you know how water expands as it rises in temperature? Well, gasoline does the same thing. The degree to which a liquid expands as it’s temperature rises is called the volumetric coefficient of thermal expansion, and gasoline has a very high coefficient of thermal expansion of .00056. You can compare this to water which has a much lower volumetric coefficient of thermal expansion of .00012. This means that gasoline expands almost 5 times more than water when the temperature rises.
This can cost you money in the summer when it is hot. If you buy 55 degree gas and then it heats up while sitting in your gas tank then you have gotten your moneys worth. If however, you buy 110 degree gas that has already expanded then you are effectively buying less than you would have if you had gone to a gas station with a tank underground.
During the winter, everything is reversed. If you buy 55 degree gas from an underground tank, your gas then shrinks in your tank as it cools down. If you buy gas that is already cold because it is stored above ground, you don’t have to pay for this shrinkage.
Is the exapnsion or shrinkage enough to make it worth your time to drive to the next station? Just how much does this effect cost or save you? Use this calculator to find out:
Maybe your tank is way bigger than mine, but when I used this calculator I found that even on the hottest or coldest day, this effect wouldn’t make more than $1.50 per tank difference to me. That isn’t enough to make a real difference, but if you are the kind of person who will drive out of thier way to save $0.02 per gallon (like me!) then you should keep this in mind.