Are you buying phantom gas, each time you fill up?

Dear Car Talk

Dear Car Talk | Dec 01, 2007


I recently saw an article on a Web site claiming that car owners should pump their gas in the morning, when it's cool out, instead of in the afternoon, when it's hot. The alleged reasoning is that gasoline expands at higher temperatures and contracts at lower temperatures, allowing more "dense" gas to be pumped when it's cold. I personally think this is nonsense, since a car's gas tank also will expand and contract, and because gas stored in an underground 500-gallon tank probably doesn't warm by more than a few degrees. So, what is the truth to this? -- Richard

RAY: Well, the expansion story is true, Richard. When gas pumps are calibrated, they're set to measure a gallon of gasoline that's 60 degrees Fahrenheit.

TOM: But when gasoline gets hotter than that, it expands. So you get less than a gallon's worth of energy for every gallon you pump. How much less? Well, the most recent congressional study we've seen found that the average temperature of gasoline sold in the United States is almost 65 degrees F. That means the average Joe is paying an extra 3 cents a gallon for phantom gasoline.

RAY: What can be done about it? Well, you can fill up in the middle of the night. But a better solution would be to use pumps that compensate for temperature fluctuations. In Canada, where gasoline usually is COLDER than the standard -- which is to the consumer's advantage -- it was the gas stations that voluntarily backed a program to use those pumps. Quelle surprise, as they say in Quebec!

TOM: But here, where the gas stations are getting the extra money, they argue that retrofitting their pumps is too expensive. They say it would cost $1,500-$3,000 per pump.

RAY: But with the value of the phantom gasoline sold adding up to more than $2 billion a year now, the pressure on the gas stations will probably continue to heat up. Now, if they'd agree to put that 3 cents a gallon toward clean bathrooms, maybe a compromise could be worked out here.

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