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The Spokesman-Review Newspaper
Spokane, Washington  Est. May 19, 1883


Octane apprehension

The quandary of whether to opt for higher-cost premium fuel stirs much debate.  Will it harm vehicles designed to run on regular?  Will it help those vehicles?  Must one use premium if the manufacturer requires it?  What harm is done not using it when it’s recommended?

Those concerns weigh on many motorists’ minds.  When considering new cars, consumers note that manufacturers specify premium fuel for some models.  And if a local dealer says you can ignore that, they are generally correct. 

Much of the anecdotal advice for fuel use is based on personal bias or speculation.  Some say that premium fuel offers better mileage.  Not true.  Others may say they can feel the performance difference.  Probably not true.  Without sanctioning acceleration tests verified by a stopwatch, it’s difficult to notice slight horsepower variations.  Detecting small performance drops or rises from the driver’s seat is unlikely.

Prejudice and superstition aside, experts (engineers and technicians) generally agree that the need for premium fuel use is miniscule and, at times, detrimental.

The nomenclature is a bit misleading.  “Premium” fuel does not mean that it’s better, but simply that it has a higher octane rating; the higher the octane, the slower the burn.  Though manufacturers may require only regular, recommend premium or require premium, all modern cars (after mid-1990s) can likely use regular with no adversity.

The only damage that can result from downgrading fuel is when an engine undergoes extended pre-detonation, spark knock or “ping” (all the same thing).  Pre-detonation is when the fuel mixture ignites too quickly, during a piston’s up-stroke.  But cars made after the mid-1990s (some even earlier) have advanced computer software monitoring timing and ignition functions.  When these systems sense spark knock they respond by adjusting ignition timing to eliminate its occurrence.  If your vehicle has an audible “ping,” there may eventually be adverse effects, but new vehicles simply don’t let that happen regardless of fuel used.

When a manufacturer “recommends” or even “requires” premium fuel, it is mainly to advertise a certain performance level (horsepower) on upscale brands.  They certify horsepower and acceleration figures based on the use of premium fuel.  The decline in those statistics resulting from the substitution of regular fuel is estimated to be less than five percent. 

If you want the maximum performance from your “premium required” vehicle, then premium fuel is warranted.  You will not, however, do harm by substituting regular unless you hear the tell-tale knock (sounds like a rattle) of pre-detonation, which is unlikely in a newer engine.

Performance will not be enhanced by using premium in an engine designed for and only requiring regular fuel.  Most important is that fuel be clean and contain additives.  With the proliferation of fuel-injected engines, most gasoline processors mix additive packages into their products.

Additives differ by brand more than by fuel grade.  That means that when you buy a quality regular fuel, you will benefit from injector-cleaning properties just as you would with premium fuel.  Some studies have shown that engines designed to run on regular actually perform less efficiently when burning premium.

Overall, it’s a waste of money to use premium fuel in a vehicle in which only regular is required.  Using premium in a modern vehicle when it is recommended or required maximizes performance, but substituting regular will not cause harm or void a warranty and the decrease in performance will be virtually undetectable.

Readers may contact Bill Love via e-mail at