Can you really put more gas in your fuel tank when it’s cold?
Have you ever heard the advice to fill up your car with gas first thing in the morning? This fuel economy myth posits that because gasoline shrinks in the cold, you’ll get more for your money in the morning. The truth is that gasoline shrinks when it cools, but it’s unlikely to change much in temperature in underground gas station storage tanks.
Gasoline expands and contracts with temperature
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According to Snopes, gasoline expands or contracts 1% for every 15 degrees of temperature change. If a gallon of gasoline cools, it shrinks slightly and takes up less than a gallon of space. Likewise, if that gallon of gas gets hot, it will expand.
Lawmakers know that means not all consumers are shaken equally. Most gas pumps are set to meter gallons of gas at 60 degrees Fahrenheit. But in Hawaii, the pumps are rated at 80 degrees. Without this recalibration, a Hawaiian gallon of gas would shrink to less than a gallon at lower temperatures.
Other lawmakers have proposed switching to gas pumps that use a technology called Automatic Temperature Compensation (ATC). These fuel pumps measure fuel temperature and adjust their volume measurements accordingly.
Is it worth pumping gas early in the morning?
It’s probably not worth pumping your gas very early in the morning to save money. Although gasoline contracts a little when it’s cold, morning gasoline is probably the same temperature as night gasoline, maybe warmer.
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Snopes fact-checkers point out that gasoline is stored in huge underground tanks, deep under gas station parking lots. These tanks, the dirt and concrete around them, and the amount of gasoline they contain, all work together to insulate the gasoline. Gasoline temperature is unlikely to be lower at a certain time of day.
Pumping your gas early in the morning can actually be bad. If the oil company delivers fresh gasoline to your station in the morning, the fuel straight from the refinery may actually be very hot. Obviously, this gasoline in underground tanks will stay hot for quite some time. If you pay for a full tank of this hot gasoline, it will cool and shrink later.
Can cold gasoline save you money?
Some scientists have pointed out that gasoline does not gain more “energy” when it shrinks or expands. Therefore, cold, constricted gasoline will likely increase your MPG. Hot, expanded gasoline will reduce it. Therefore, you will get as many miles/dollar each time you fill up.
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Finally, even if buying cold gas early in the morning allowed you to get 1% more fuel with each fill-up, that 1% in gas savings would not save you a lot of money. That 1% would translate to $31/year for the average US driver. Is it really worth getting up at dawn every time you need fuel?
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