Don't use cheaper gas in cars if premium fuel is required, experts say

LOS ANGELES — With fuel prices on the rise, some drivers are pumping less-expensive regular-grade gasoline into cars for which premium fuel is recommended.

Although that might save money initially, auto experts are divided on the wisdom of such a strategy, which some say could end up costing motorists more.

What you save at the pump can be lost on the road as the electronics in the engine ratchet down performance to deal with the lower-grade fuel, experts say. Using the cheaper gas might also damage the vehicle over a long period.

"If the owner's manual says premium fuel is recommended, then you can switch down," said Steve Mazor, manager of the Auto Club of Southern California's Automotive Research Center.

Using a lower-grade fuel will trim maximum horsepower a bit, impede acceleration and "drop fuel economy by a couple of tenths of a percent," Mazor said.

But it's not a good idea to use regular gas in vehicles for which the manufacturer says premium fuel is required, experts say.

Harold Schock, director of the Engines and Automotive Research Labs at Michigan State University, said it's not clear what the long-term effect might be on a vehicle's engine.

Modern cars have knock sensors that detect whether the vehicle is about to misfire and change the engine's timing to prevent this from happening when a driver uses a lower-grade gas. Knocking, in which gas burns out of synch with an engine's timing, can damage the motor. But the sensor stops it from occurring and prevents any immediate damage to the engine.

"If you use fuel with the lower octane rating, our engines will deal with it," said Thomas Plucinsky, a spokesman for BMW. "But why would you do it in a car like our 335i? You are not getting the power and performance you are expecting and paid for."

It's also not clear whether the repeated triggering of the sensor would eventually hurt engine life long after the vehicle is out of warranty, Schock and other automotive engineers said.

"What appears in the owner's manual is the best set of practices for operating a car if you want to get the longest life and the best performance out of it," Schock said.

Just about all of the experts agree that drivers can exact far greater savings by paying more attention to their vehicles' upkeep and their driving habits.

"It's probably better to follow the gas recommendation in the owner's manual and then learn to drive less aggressively and to slow down a bit," said John Swanton, an air pollution specialist with the California Air Resources Board. "Why handicap the vehicle's performance?"

Don't use cheaper gas in cars if premium fuel is required, experts say 03/30/12 [Last modified: Friday, March 30, 2012 11:03pm]

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