If you don’t already, fill in the morning. The temperature is coldest and you get more gas in your tank. During the day as temperatures rise, the liquid expands three times faster than water and so you actually get less per volume when the temperature goes back down.
Physics professor Michio Kaku demonstrated the concept by heating water in a bottle. As it heated up, it expanded and overflowed. In other words, it took less water to fill the same size container.
“Remember that gasoline expands roughly three times faster than water,” Kaku said. “So magnify this effect inside your gas tank.”
The flipside?
An independent fuel marketers and retailers group argues if any gasoline is lost, the amount is tiny.
“We do not see the information they have gathered as being credible,” Jay McKeeman said. “Basically it’s about a tablespoon in 12 gallons of gasoline.”
The magic number is 60 degrees. In the early mornings during the fall and spring, that could be all the difference when your morning temperature is 50 but daily high is 70.
BTW, later this week, I’ll finally get around to posting something about watered down gas and how wrong I apparently am.
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I’m a mechanical engineer by trade so I’ll have to comment on this:
Assuming that the volumetric CTE (coefficient of thermal expansion) of gasoline is 950 x 10 -6 per Celsius
From 50F to 70F is a 20F rise or 11.1C rise in temperature.
0.000950 * 11.1C = 0.01 (a 1 percent increase in volume based on the temperature rise)
So if the above was mumbo-jumbo, in plain english: purchasing warmer gasoline results in 1% less gas then what you pay for if it was colder.
At $3 a gallon, you are losing 3 cents worth of gas. Big deal. Of course the implication of this for gas companies is huge since they sell thousands of gallons to consumers.
This math all depends on where the gas tanks are located at the station you fill up at. Often they are located deep underground where temperatures hardly fluctuate because of insulation.
Gotta love physics and personal finance.
Great comment Savvy Steward! The tanks are underground and unless the ground temperature changes a lot, I guess it’s safe to buy gas at almost any time of day. I wonder if there is better insulation with double hulled tanks?
Hm… It does make me think hard though. My pop used to get most of his deliveries at night. Trucks would come there after making deliveries at other stations, and then dump whatever they had left into his tanks. Rarely did we take a delivery during daylight hours. (We were a 12 pump station in PA with some serious capacity. IIRC, about 20K gals total.)
I think the only way to save gas is not to drive so often. The other day I read an article about saving money on gas or improving mileage by keeping the windows rolled up if you’re going 55 mph or faster and blah blah blah. But when the weather is nice, what’s the fun in that! I’ll sacrifice a few pennies to feel the wind. If I’m that worried about gas, I’ll walk or stay home.
The metapoint of this is less about the 3 cents and more about planning. I save a lot of money on gas when I *plan* my purchases, know when they’re coming, reduce driving, and yeah, fill up in the morning. The worst is when I am randomly low on gas. Nice post, (and I loved my physics lesson from Savvy Steward up yonder.)