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Experts
knock premium
Pricey
gasoline doesn't benefit most kinds of automobiles
BY MARK PHELAN
DETROIT FREE PRESS BUSINESS
WRITER
What difference does it make if you use regular or
premium gasoline in your car?
About
20 cents a gallon.
It
may be small comfort with gas prices remaining so high, but you virtually never
gain anything by running a higher and more expensive grade of fuel than the
manufacturer recommended, and you may not lose much if you use a lower grade of
fuel, a variety of experts say.
A
lot of people fill up with premium every third or fourth tank. Some do it to
clean out the engine, some to get a little more power or help an older engine
run smoothly.
It's
a nice idea, but they might as well toss 20 cents a gallon into a wishing well.
"It's
a waste of money," said Harold Schock, professor of mechanical engineering
and director of Michigan State University's Automotive Research Experiment
Station, which studies combustion systems.
"It
doesn't make any difference for most people," Schock said. "Most
engines are designed to operate on relatively low-octane fuel."
There
is no power difference from high-octane premium to low-octane regular, said
Robert Furey, a fuel specialist with General Motors Corp.
"Octane
is simply a fuel's resistance to knocking," he said.
"There's
no benefit if the octane is higher than the engine needs, but if it's too low,
that can cause knocking," he said.
Engine
knock -- what happens when fuel in a combustion chamber ignites before it
should, causing a disruption in the engine's operation -- used to be a major
concern, but devices called knock sensors have nearly eliminated it, said Pete
Dowding, manager of Ford's modular V8 and V10 engine program.
Before
electronic knock sensors became common, a bad tank of fuel could be disastrous,
because persistent, severe knocking can destroy an engine, Furey said.
"If
you find your car runs fine on a lower grade of fuel, go ahead," said Bill
Hickman, spokesman for the American Petroleum Institute. "We don't
encourage people to buy a higher grade. Just follow the manufacturer's
suggestions."
Some
automakers still say premium is required for their high-performance engines,
but even they admit it's more of a suggestion than a command.
"Based
on our high compression ratios, it's important to use premium," said Rob
Mitchell, spokesman for BMW of North America.
"However, you can run on regular if no premium
is available. We don't recommend it, but it won't damage the engine. There is a
slight deterioration of performance, however."
Running
regular fuel in an engine designed to use premium does reduce performance and
fuel economy, Furey said, but too slightly for most drivers to notice.
GM
requires premium for just two engines: its supercharged 3.8-liter V6, used in
the V6 Buick Regal GS, and high-output 1.8-liter four-cylinder in the Pontiac
Vibe GT.
Even
the Chevrolet Corvette runs fine on regular, Furey said, although GM recommends
premium for maximum performance.
On
the other hand, some engines have sophisticated two-way knock sensors, which allow
them to generate more power if you use a higher-octane fuel than the
manufacturer recommends. Chrysler reportedly fits some of its engines with such
sensors, meaning that a fill-up with premium actually can put a tiger in your
tank.
Contact
MARK PHELAN at 313-222-6731 or phelan@freepress.com.
Posted April 3, 2003
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