Six Myths About Improving Gas Mileage

Especially with gas prices rising again, myths and rumors about how you can increase gas mileage are spreading like wildfire, from the ridiculous to the real thing. Snopes and Mythbusters have tackled some of them – like whether it’s better to run your AC or drive with the windows open or if acetone improves mileage – and now CBS MoneyWatch has busted six more.

Check ‘em out:

1. If your owner’s manual says “premium fuel recommended,” you’ll ruin your car by filling it up with regular.

Reality: Unless you’re driving in the Indy 500, using regular gas in a car that says premium fuel is merely “recommended” is perfectly fine. And doing so will save you 25 cents per gallon.

“Unless you have a job that requires regular sessions on a racetrack, there is no legitimate need to ever put premium fuel in your vehicle,” says Susan Winlaw, co-author of the book, Car Advice for Women (and Smart Men). Using regular gas could cost you a few horsepower when you’re driving at higher speeds, but chances are you won’t notice the difference, and it definitely won’t hurt your car. Your engine’s fuel-management system is perfectly prepared to handle lower-octane fuel, says Winlaw.

On the other hand, switching to regular in a car for which premium fuel is “required,” as it is for a few high-performance luxury rides, could cause noticeable knocking. And over time, that could lead to faster engine wear.

Those cases aside, just how much could switching to regular gas save you this weekend? According to the AAA’s Daily Fuel Gauge Report, the national average price per gallon recently was $2.68 for regular gas, versus $2.94 for premium. A longish road trip could account for four fill-ups of about 20 gallons each, meaning you’d save almost $21 by using regular gas over premium.

2. In the summer, you should only buy gas at night or early in the morning when the gas is cold. Because cold gas is more dense, you’ll get more fuel for your money.

Reality: Buying cold gas is a lot harder than it sounds, and the potential savings are scarcely worth it.

Consumer Reports thoroughly tested this theory using their own underground tank, similar to those used by gas stations. They found that it’s surprisingly hard to accurately predict whether a given tankful of gas will be cold or warm. For starters, if gas was a given temperature when it was delivered from the tanker truck, it tended to stay that temperature for a while, even after it had been transferred. Not only that, but the first gas to be pumped in a given day could be warm because a certain amount of gas collects in the aboveground pump. So even if you manage to be the first customer of the day, you might still be buying warm gas.

After all that, even if you’re successful in buying cold gas, the difference in density is so slight — perhaps a maximum of 1 percent per fill-up, according to Consumer Reports —that the savings are marginal. “It’s an urban myth” that you should always buy gas at night or early in the day, says Gabriel Shenhar, senior auto test engineer for Consumer Reports.

Get the next four myths over at CBS MoneyWatch.

Link [CBS MoneyWatch] via [Pumps]

Photo: Flickr user kwc

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