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Premium gas can be a waste of money

Consumer Reports News: July 22, 2008 05:08 AM

Many people use premium gasoline thinking that it’s better for engines than regular. That can be a costly misconception.

Regular gas typically has an octane rating of 87, while premium is rated at 91 to 93. But octane grades don't represent "good, better, best"; they simply measure a fuel's resistance to pre-ignition (pinging or knocking), a condition in which gasoline burns uncontrollably in the engine’s combustion chambers, possibly leading to engine damage. The higher the octane rating, the more resistance it provides.

Most engines are designed to run fine on regular gas. Using premium in them doesn’t improve performance; it only costs more money.

Even many cars for which premium is recommended can use regular gas without a problem. That’s because most modern engines can detect the presence of pre-ignition (which usually occurs under high-load conditions) and automatically make adjustments to eliminate it. The tradeoff when that happens is a slight decrease in power and gas mileage, but most people probably won’t notice it.

Generally, if your owner’s manual says "premium recommended," you can safely use regular gas.

Some engines do require premium gas. They’re typically more powerful ones used in sports and luxury cars. Those engines use a higher compression ratio, which can make them run hotter and make them more vulnerable to pinging. The high octane fuel helps them resist the condition. So if the manual says "premium required," follow it.

Learn how to save at the pump by visiting Consumer Reports’ guide to driving green. Check the latest national average gasoline prices.

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