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Dec 21, 2007 10:22 pm US/Mountain
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Experts Say Lower Octane Fuel OK
Good Question: Does My Car Really Need Higher Grade Gasoline?
DENVER (CBS4) ―
Ask them at the pump and you'll get different opinions: "I usually do. Makes the engine run better I think," said the man with the sporty Volvo turbo. "Never, never put premium in," said the woman filling up the Jaguar.
Many of the experts though say there's little damage to the car. Downing Street Garage Master Technician Bobby Saunders says, "It's not recommended by the manufacturer but you might be able to get away with it."
Colorado has lower octane fuel than many states around the nation because our air doesn't need it.
"We have colder air, we have less air density so we're able to burn a lesser octane fuel," says Saunders.
If you used an 85 octane at sea level in a car with a demanding engine that seeks premium says Saunders.
"When you'd step on the accelerator there'd be so much pre-detonation it would sound like the motor's coming apart."
That's the knock you get when the engine is struggling. The knocking is actually more violent detonation of more explosive gasoline. The lower the octane the more explosive.
"You notice it has a quick flash, kind of a boom to it," Saunders says. "But when you light charcoal lighter, using charcoal lighter fluid, you get a much slower burn, that's like a higher octane fuel."
Vehicles built with fuel injection over the last dozen years or so have knock sensors. It senses when there's lower octane fuel.
"When the computer senses that knock, it retards the timing as far as it can to control the knock. It will also enrich the fuel mixture bring it up and try and do away with the knock."
So cars adjust for lower grade fuel. If the car knocks, the knock sensor can't compensate for the difference.
Will it affect power? "Um, maybe slightly," says Downing Street Garage service manager Misty McNett. "Probably more like if you're in the mountains."
But higher octane isn't the only reason to go for the pricier gas. The service manager for a local BMW dealership told us, "Keep in mind that just because a gas is 91 octane level, it doesn't necessarily mean that it's a good gas."
"The 'quality of the refine' is what determines how good a gas is."
He's talking about detergent content. The government has allowed refiners to lower levels of detergent over the years. Some add more, some less.
"You know you'll have your cheaper stations and your more quality stations, where you're going to pay less you're probably not going to get the detergent additives," says McNett.
Detergent helps keep injectors and other engine parts from getting covered with the crud that ends up in your gasoline. It can mean reducing your need for a tune-up. Detergent helps keep the particles floating in the gasoline, so it is burned.
So while you may not want to shell out for higher octane fuel McNett says, detergent might keep the costs of servicing your car down, making it worth the price. "In the long run it is."
Still have questions? Call your car dealer and ask if using a lower octane level will endanger your warranty. Many now suggest gas for their vehicles with higher detergent levels.
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