Separating gas-saving facts from fiction


Doing the right thing can increase your gas mileage as much as 33 percent. But doing the wrong thing can both reduce your gas mileage and cost you money.

As the price of gas remains high, there are a number of myths about saving gas. Perhaps the most popular has to do with your air conditioner.

"I don't turn the AC on, I roll the windows down," said Fred Nickel from San Francisco.

That's good advice if you're on city streets. But trying that on the freeway actually decreases your gas mileage.

"If you are in the freeway, then the drag is increased by having your window open," said U.C. Berkeley Mechanical Engineering professor Carlos Fernandez-Pello, Ph.D.

Increased drag means your engine has to work harder and use more gas. On the other hand, the drag is minimal at slower speeds. So turning your air conditioner off and opening your windows does work on city streets.

Professional race car drivers say gas by using a technique known as drafting. The vacuum of air left in the wake of a car speeding at 150 miles an hour actually reduces drag and conserves fuel.

But drivers trying to replicate that on the freeway would have to get dangerously close to a semi-truck in front.

"The savings I don't think are worth the savings considering the potential risk of an accident," said Fernandez-Pello, Ph.D.

Others desperate to save gas have added water to their gasoline thinking they would save gas.

"That's another of the myths," said Fernandez-Pello, Ph.D.

Still, others spend their money on various gadgets and products.

"I bought an octane booster for my engine," said Bob Rehfeldt from Mill Valley.

A study by the Environmental Protection Agency found most gadgets sold do little to save gas, some do nothing at all.

The professor says the best ways to save gas are to avoid rapid acceleration and fast stops, maintain your tire pressure and keep your air filters clean.

The optimum speed is between 45 and 50 miles an hour and finally, keeping your gas tank full decreases evaporation.

Related links:

  • Information about our voluntary testing program
  • List of registered fuel additives
  • Green vehicle guide
  • Fuel economy
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