Running on Empty

June 5, 2008— -- With gas prices continuing their steady climb, some drivers are buying a little gas at a time instead of filling up their tanks. That means they may drive with the tank close to empty.

This raises a question we've checked out once before: When your gas gauge reads empty, is it? Does empty really mean empty?

Last fall, I ran a test. I bought a spare can of gasoline and set out on a road trip -- a trip that started with next to no gas in my minivan's tank. When I left New York City, the car's gas light was on and the needle on the gas gauge was near "E."

Luckily, my car has a feature that seems more precise than the needle: a digital read-out. It said that I still had 25 miles to go.

If that's true, what does empty really mean? Is it when the needle hits "E"? Is it when the digital read-out hits zero? I kept driving. Would the car stop moving when the read-out hit zero?

It didn't.

My car still kept going. And going, and going, and going.

Of course, I wasn't the first person to test the limit of a car's gas tank.

Last summer, when computer programmer Justin Davis was traveling through Canada in his Honda Civic, he found himself close to the border with a near-empty gas tank. Canadians pay more than double the gas tax that we do in the United States, so Davis wanted to try to get to a U.S. gas station, but he chickened out.

When he got home, he started a Web site called TankOnEmpty.com in which he asked "How far can you go after the gas light in your car has gone on?" More than a thousand people posted their stories on his site, giving Davis data on how many miles they were able to go after their car's gas light came on.

The results? According to Davis, most cars can travel an additional "30 and 40 miles after the gas light is on." He reasons that most of these drivers probably get scared and don't push their car to its true limit. Nevertheless, he says, some brave drivers drove as far as a hundred miles after the gas light came on.

I was reluctant to try this because I'd heard driving until the tank's dry damages your engine. But engineers we spoke to said if you run out of gas once in a while, you're fine. It's only if you repeatedly drive until empty that you risk shortening the life of your fuel pump.

So why do cars say "empty" when there's still gas left? Ford said it's about providing a "comfort zone" for the driver -- you don't want to have the light go on and all of a sudden, you're dry. GM said that customers in the United States want that reserve, and they provide it. Chrysler said some drivers, German customers, for example, want to know exactly how much gas is in the tank, but Americans like to have a buffer.

I learned that my van has quite a buffer. After the digital read-out hit zero, I thought I might be able to travel a few miles until the car gave out, but my car kept going for 40 more miles before running out of gas, and that was 65 miles AFTER the dial said "Empty"!

So the next time you panic at the sight of a gas gauge on "E," remember that you probably have enough gas to make it to the next station. "E" doesn't really mean "empty," after all.

ABC News' Andrew Sullivan contributed to this report.

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