If you've stopped buying premium gasoline, you are not alone. Nor are you alone if you're worried about what low-octane fuel is doing to your car.
Faced with higher gas prices since the Iraqi invasion of Kuwait last August, many motorists are trying to keep money in their pockets by filling their tanks with medium-grade or regular unleaded gas.
Federal standards say regular unleaded gas must have an octane rating of 87, while mid-grade gasolines have ratings of from 89 to 91 and super or premium grades have ratings of 92 to 94. In Maryland, the state monitors service stations to assure the octane levels of the gasoline sold.
But experts disagree over the importance of using higher octane fuel. Some say any octane level above that required to avoid engine knock or power loss is a waste of money. Others say using high-octane gasoline improves performance and mileage.
However, the experts agree that if the octane level is too low to prevent knock in a particular car, the result can be engine damage that is far more costly than buying premium gas would ever be.
Octane, a complex hydrocarbon, determines how fast a fuel burns, according to Pat Willingham, shop foreman at Herb Gordon Dodge in Silver Spring.
The faster a fuel burns, the more prone the fuel is to knock, or ping -- the tapping sounds most frequently heard in most engines that are working hard while accelerating or climbing hills.
Knocking is caused by premature ignition in the engine's combustion chamber -- gas exploding before it should and hitting the pistons before they've reached the top of their cylinders. Gasoline with a high level of octane burns slower, thus eliminating premature ignition and knock.
"People ask all the time what octane they should use -- they ask if they can get away with the mid-grade," said Scott Fahdt of the Citgo station in Towson.
The price of premium apparently has convinced many motorists that regular gas is good enough.
Last Monday, the Crown station on York Road and Stevenson Lane sold 1,600 gallons of regular, 500 gallons of mid-grade, and only 315 gallons of high-test gasoline, according to John M. Heying, the dealer.
Sales of regular "are always higher, but we used to sell more of the other products," Heying said. "And I've talked to other dealers and they've said the same thing."
Prices for gas at the Crown range from $1.25 a gallon for regular to $1.45 a gallon for premium unleaded.
Mike Osborne used to fill the tank of his 1983 Thunderbird for under $20. He used to treat the six-cylinder car to premium gas with an octane rating of 92.
Those days are over.
This week, Osborne filled the tank with mid-grade gasoline, which has an octane level of 89. "Sometimes I mix half of one and half of the other if they let me," he said, adding that doesn't like to put regular gas, with an octane rating of only 87, into his car.
"I don't like to do that to the motor," he says.
Ruth Green, who was visiting her daughter in Towson and drove to Maryland from Cincinnati, said her Ford van "pings and makes a noise" when she uses regular gas. Green spent $98 on fuel for the 10-hour drive.
"It costs a lot to fill up," she said.
And although Trisna Sutjipto prefers to use premium gas for long trips in her 1989 Honda Civic, she has also started buying medium-grade since the price went up.
"It really depends on the prices," she says. "I went to Illinois and they had 93 octane for $1.20, so I bought that."
But how much octane is really enough?
If your car knocks or "pings" frequently, chances are the octane level in the gas should be higher.
Some experts say that occasional knocking -- when driving on a steep hill, for example -- is to be expected.
"That would indicate that you're right around the right level," said Howard Hoffman, editor with Hydrocarbon Processing Magazine. After the car stops knocking, he adds, higher levels of octane are not required.
W.J. Barton, staff and technical adviser for Exxon Co. USA, agreed.
"If the car does not knock, then it means that the fuel you're using is appropriate," he said.
But Willingham said that even infrequent knock or ping is a problem and should be corrected.
"Knock can occur to the point where it's not audible, but it's still doing damage to the engine," he said. "Under continued use, [a low-octane gas] will burn holes in the piston." And, even if the the car has stopped knocking, using high-octane gas can sometimes improve a car's mileage to where it offsets any additional cost, said Willingham.
"We have found cases where it's cheaper for people to get high-test because the engines are so much more efficient," he said.
The exceptions to the knocking rule are cars equipped with knock sensors -- equipment that can detect knock and adjust to it. Though the engine might not knock, a loss of power or increasing hesitation may indicate the octane level is too low.