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Premium Fuel: The Myth and the Truth

January 29, 2009

For years I have taken it for granted that there had to be different grades of gasoline at the pump in order for your vehicle to run properly.  I used to drive a very high performance Camaro that required the highest octane fuel available because this vehicle had over 300 horsepower after it had been modified and Dynamometer tuned by a well known speed shop.  It was one of the original 1967 Z28 Camaros with the famous 302 cubic inch engine.  For years I have been filling up my vehicles with middle-grade, 89 octane fuel, even though it costs more than the basic 87 octane gasoline.  No more, and I will tell you why.

I began following work from Bill Wattenburg, a well-known radio personality and scientist who has worked at the Lawrence Livermore Research Labs and at UC Berkeley teaching both Physics and Electrical Engineering.  He began speaking about the fact that the modern vehicles, especially the ones with Direct Ignition Systems and without Distributors, are required to pass a very stringent EPA-conducted test in order to be sold in the US.

This test requires that all the vehicles be tested on regular gas, i.e., 87 octane gasoline.  All the vehicles must pass numerous, extensive, and very strict dynamometer tests that measure 27 gases from the tailpipe (a typical emissions test measures up to 5 gases).  As it turns out, this same criteria is used for a vehicle to be California Emissions Certified.  The modern Powertrain Management Computers automatically adjust the Spark Timing to best utilize the octane level in the fuel tank.  With this information in mind, I decided to take action and run 87 octane in my own 1998 Toyota 4 cylinder Camry.  I have had no problems whatsoever.

For the past 3 years, I have been conducting an experiment with my girlfriend's Turbo Passat.  The Dealer swore up and down that if she ran 87 octane it would ruin her engine.  I am pretty familiar with her engine and its "Coil Over" ignition system.  We have put 30,000 miles of driving, including spirited romps up to the Sierra Mountains, wailing up the steep hills of the mountain highways, and her car still runs perfectly fine.  There has not been one iota of harm done to her engine as proven by boroscope inspections of her combustion chambers.

So, why do the Oil Companies sell 91 octane, 89, octane and 87 octane?  They must be profitable, and perhaps many customers are really interested in eking out a few more horsepower.

Next week: some thoughts on the Plug-In Hybrids

About the Author

Daniel Dillon is an automotive expert at RepairPal, the leading online source of auto repair resources and estimates. With many ASE Master certified mechanics on staff who have decades of experience, RepairPal knows all the fine points of car repair.

1 User Comment

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By , July 28, 2017
My 2006 Audi A4 Avant-garde Quattro w/6speed manual indeed hesitates if I use less than 91 octane. I've know others that use 89