Consumer Reports wants you to know that it’s OK to sleep in, because you’re not going to save money by pumping gas in the early morning. Why not?

The basic facts are correct, but the advice is not. Gasoline does expand and contract a little depending on its temperature. When gasoline rises from 60 to 75 degrees F, for instance, it increases in volume by 1 percent while the energy content remains the same.

But filling stations typically store their gasoline in underground tanks, where the temperature variation during the day is much less than in the air above. The result is that the temperature of the gasoline coming out of the fuel nozzle varies very little, if at all, during any 24-hour stretch at any particular station.

CR did some temperature testing at their auto test facility where they have an underground fuel tank similar to the ones that gas stations use. Here’s what they found:

While the air temperature between filling varied by up to 12 degrees, the fuel in our underground tank stayed at a steady 62 degrees F. As a result, we found that after the first few gallons were pumped, the fuel temperature coming out of the nozzle varied very little between morning and afternoon.

Like a hose sitting in the sun, gasoline that was sitting in a pump and not being dispensed tended to warm up– but those few gallons didn’t make much of a difference. Ultimately, CR found that there was no reason to pump in the morning.

Even with the temperature swings we saw in the first few gallons pumped at our facility, we didn’t see a big penalty for the consumer. A 15-degree difference, for example, would result in a one-percent gain in volume. Or, just a few cents difference on the first gallons pumped—not enough to change your schedule or routine in chasing costs, especially if it might increase your fuel consumption in the pursuit.

You can get the rest of the details of their testing by clicking here.

Save on gas with morning fill-ups? Don’t bet on it [CR]
(Photo: Listener42 )

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