As gas prices soar, tips on how to save money are mostly myths
Luke Daughtery, 9, fills up the car Thursday at Chills gas station on South Fourth Street in Danville. His mother, Sondra, was waiting in the car. (Clay Jackson Photo)
Rumors about ways to fill your gas tank without draining your wallet are as ubiquitous as ever as local prices rise above $3.50 a gallon for regular unleaded gasoline.
“They’re really sticking it to us,” Danville resident Betty Keeton said at Chills Quick Stop on Hustonville Road. “I’m trying to do the best I can.”
Unfortunately, gas prices don’t seem likely to fall anytime soon. So mass e-mails about tips on pumping gas are appearing in inboxes across the county once again.
But, when Jeff Fieberg, an associate professor of chemistry at Centre College, took time to sort the myths from the money savers, he found little scientific evidence to support the most popular rumors.
First on the list: It’s best to fill up when the tank is half full because the less air in the tank, the smaller the opportunity for gas to evaporate.
Fieberg said this explanation holds some scientific weight, but won’t do much to keep pocketbooks heavy.
Letting air occupy the majority of space in the gas tank does increase the potential for gas to vaporize. But keeping the tank half full would only increase the amount of useable liquid gasoline by about one milliliter, which is equal to 20 drops from a pharmacy dropper, per fill up.
“It’s basically a negligible amount,” Fieberg said. “It wouldn’t be something you’d want to do if you’re trying to save money.”
A second common tip advises drivers to fill up their tanks in the morning because gas expands as it heats, causing hoses to deliver a less dense gallon of gasoline.
True, vapors do expand as gas becomes hotter.
In fact, if the temperature of liquid gasoline increased from 70 degrees to 110 degrees Fahrenheit, it would turn to a gaseous state about five times as fast, Fieberg said.
However, the tanks storing gasoline are kept underground where temperatures in Kentucky are unlikely to change 40 degrees from morning to night.
The temperature variance that does occur probably isn’t enough to substantially effect the density of the gasoline we buy, Fieberg said.
A third, and not so charmed, trick explains that drivers should fill up their gas tanks slowly, otherwise more gas will vaporize and get sucked back into the hose.
This myth seems to operate under a misconception about temperature, which is the main factor causing a liquid to become a gas, Fieberg said.
Temperature describes the speed that molecules in a substance are traveling, not how fast the actual substance is moving.
So even if a customer pumped gas as quickly as the hose would allow, it’s unlikely that the temperature would rise enough for gas to vaporize, he said.
“I don’t think you’d save any more for the amount of time you’d sit there going slowly,” Fieberg said. “I personally wouldn’t do any of these to save money.”