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No, filling up in morning or at night won’t save much money on gas

Fuel experts agree filling up in the coolest part of the day doesn’t make a difference, since most pumps temperature-correct.

GREENSBORO, N.C. — The cost of gas is guzzling away at hard-earned paychecks.

Despite a brief reprieve from record-high prices this week, fuel analysts warn of a very expensive summer. 

With everyone looking for ways to save, 'helpful hacks' are pumping through social media, claiming to pump the brakes on excess spending.

THE QUESTION

Viewer Janice Sumner shared some 'tips from the 'experts'" on Facebook. The top tip is to 'fill your tank late in the evening, in the coolest part of the day.'

Is it true filling up in the evening or morning saves significant money on gas?

Credit: WFMY

THE SOURCES

THE ANSWER

No, filling up in the coolest part of the day -- morning or evening -- won't save a driver much money on gas. It likely isn't worth chasing costs to fill up in the morning or at night, especially if the driver is making an extra trip to the gas station.

WHAT WE FOUND

It's basic physics -- gas expands when heated. Gas is denser when it is cooler, so theoretically, a car gets more energy per gallon if filled up in the coolest part of the day. That is accurate, but De Haan explained the change is minuscule.

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"A lot of stations temperature correct on both sides, meaning when the temperature is above or below a certain threshold, the pumps are calibrated to take into consideration the temperature differentials. By the way, we're talking about basically the equivalent of very small drips. This isn't going to be a noticeable thing," De Haan said.

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The same is true for morning fill-ups. Consumer Reports tested the theory, pumping in the cool early morning and warm afternoon. At both fill-ups, the first few gallons were notably warmer than the latter gallons, because the gas had sat in the pump dispenser.

However, the temperature-controlled gas in the underground tank quickly compensated for those initial gallons. Consumer Reports also concluded a 15-degree difference in air temperature between fill-ups caused only a one percent difference in gas volume.

"These pumps are always calibrated by departments of agriculture in weights and measures, so this is not the way to save more than 10 cents. This is just small peanuts," De Haan concluded.

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