- The Washington Times - Wednesday, March 10, 2004

Annapolis resident Mike Reinhard figured that regular unleaded gasoline was cheaper, so he pumped the 87-octane formula into his Jaguar. The Internet consultant already had downgraded from premium to midgrade gasoline before making the shift to regular unleaded.

Then, last fall, a radio program said the regular gas could be damaging his car’s engine. He has not dared use anything but premium since, even if he “can’t tell the difference as far as performance,” he says.

Is Mr. Reinhard making the right decision at the pump? His car’s owner’s manual and the printing inside the gas cap recommend he use premium unleaded gasoline, as do most manuals for high-performance vehicles.

The manual for BMWs encourages drivers to use premium-grade unleaded gas, says Mack Parrish, a two-year BMW owner and general sales manager at BMW of Fairfax. He finds that premium gasoline, which has the highest octane level, improves gas mileage by three to five miles per gallon, depending on the model of the BMW, and helps preserve the vehicle’s engine.

Occasionally, Mr. Parrish pumps regular unleaded instead of premium, realizing, “It’s not a big deal.”

He compares using premium unleaded gas to taking a daily vitamin — it’s not noticed when a day or two is missed, but a difference is seen over the long term by helping the vitamin-taker feel better.

Premium, midgrade and regular gas differ according to their octane ratings. Premium unleaded gasoline has the highest level of octane, rated at 93. Regular unleaded is rated at 87, and midgrade unleaded, a few points higher. The octane rating specifies the gasoline’s resistance to burning or detonation; a higher rating means the gasoline burns slower when it is ignited by the spark plugs and offers greater resistance to engine knock or pinging noises during combustion.

Computerized fuel injectors have been used since the mid- to late 1980s to regulate the mix of air and fuel going into the engine, helping prevent engine knocking, according to the American Petroleum Institute.

Knocking occurs when the compression ratio is too high or the timing is too early, causing the gasoline to burn so fast it explodes. If too much gasoline is injected, too much fuel will mix with air and prevent the gasoline from burning completely, causing it to soak into carbon deposits and be released in exhaust emissions. If the knocking continues over an extended period, pistons and other parts of the engine can be damaged.

“In most vehicles, no benefit is gained from using gasoline that has a higher octane number than is needed to prevent knock,” says Susan Hahn, spokeswoman for the American Petroleum Institute, adding that some vehicles equipped with a knock sensor may see “slightly” improved performance when a higher octane gasoline is used.

Lon Anderson, director of public and government relations for AAA Mid-Atlantic, agrees that pumping a higher grade of gasoline into vehicles that require a lower grade will not improve their performance and is “a waste of money.”

“The octane rating tends to be what manufacturers recommend,” Mr. Anderson says. “A better grade of gas is better for [all] cars turns out not to be the case. … It’s the single biggest mistake motorists make.”

Each grade of gasoline increases in cost by an average of 5 cents to 10 cents, he says. In early March, the average price for regular unleaded gas in the D.C. metropolitan area was $1.66; mid-grade, $1.76; and premium, $1.81, 4 to 6 cents below the national average.

Most vehicle manufacturers recommend the use of regular unleaded for cars, trucks and other vehicles, including hybrid vehicles powered by a combination of gasoline and electricity.

Gasoline is a mixture of hundreds of hydrocarbons that are the lightest organic compounds produced from refined crude oil. The heavier hydrocarbons form diesel fuel; the heaviest, asphalt. Gasoline is formulated according to commercial standards established by ASTM International, formerly called the American Society for Testing and Materials, so that it can be used “in a variety of vehicles under a variety of conditions,” Ms. Hahn says. Oil companies are not required to follow the standards, though each state can adopt them into their requirements.

The standards allow “the product to be distributed around the country through a network of pipelines that extend from the refineries to about 1,200 terminals,” Ms. Hahn says. “Each major oil company then adds its own specific additive package to this basic recipe for gasoline. … Different companies have different additives that make gasoline a finished product.”

The Clean Air Act requires gasoline to include one additive — a certified detergent that prevents carbon deposits from developing; keeps the fuel system clean from the fuel tank through the injector; and reduces exhaust emissions of oxides of nitrogen, carbon monoxide and unburned hydrocarbons.

Other additives can include corrosion inhibitors to protect the fuel system and engine parts from rust and corrosion; antioxidants and metal deactivators to prevent the formation of gum and other harmful compounds in stored gasoline; and de-icers to prevent ice from forming in the fuel system and fuel in cold weather.

“Most of the additives… help keep the engine running well throughout its life,” says Peter Lidiak, senior product associate for the American Petroleum Institute.

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