High cost lowers demand for premium gas

Terry JacksonTurn on the TV and you'll see that CNN is keeping a running count on the number of days in a row that the price of gasoline has fallen. At last count, it was more than 30 days, and the price of a gallon of regular is now about $3.70 on average nationwide.

Encouraging, yes, but the fall has not happened as quickly as the rise, so consumers are right to still be concerned.

There's another trend that may help consumers at the pump, and that's a subtle turn away from premium-grade gasoline by automobile manufacturers -- mostly Ford and General Motors -- and an even greater shift among consumers.

Until the gas price explosion of 2008, manufacturers were eager to tout more horsepower for their vehicles in part by tuning the engines to get maximum performance using premium-grade gasoline.

This grade of gas generally rates at 91 to 93 octane (versus 87 octane for regular) and costs 20 cents to 30 cents more a gallon.

Overall, about 62 percent of all new cars come with recommendations that owners pump premium for maximum performance, up from less than 50 percent of cars in 2002.

Yet there are indications that drivers are forgoing the added boost of premium and

running regular or 89-octane mid-grade fuel instead. Demand for premium at the pump has fallen more than 50 percent in the last 10 years.

This year, Ford is touting that all its vehicles -- save perhaps the ultra high-performance

Mustangs -- can run on regular fuel.

And even though all BMWs sold in the United States come with a "premium recommended" sticker, the company acknowledges that all will run on 87 regular accompanied by a slight drop in performance.

In the days before fuel injection, many drivers stepped up to premium gas as a way to prevent what is commonly called "engine knock". The knocking sound -- think of acorns rattling around in your clothes dryer -- comes from premature detonation in the cylinders.

Premium fuel, which is more resistant to the conditions that cause knocking, can help eliminate the problem, especially in carbureted cars or cars with high mileage and deposits on the intake and exhaust valves.

But most modern cars have knock sensors built into their computer controls that regulate when the spark fires in the cylinder. This helps eliminate the problem. Those knock sensors can also detect when a lower grade of fuel is being used and adjust the engine's performance accordingly.

The only issue for owners is to carefully read their car's manual for any language that would suggest a warranty issue if the vehicle is run for long periods of time on regular grade as opposed to premium. Few but the most exotic of cars would likely have such exclusions.


So even though gas prices are falling, you may be able to save $5 to $6 per fill-up by switching from premium to regular with only a modest -- 5 to10 horsepower -- drop in performance.

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