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4:27 PM Thu, Nov. 15th

Why do you buy the expensive stuff?

I was working at a Mobil full-service gas station in Ahwatukee when I was attending Arizona State. I would fix cars and bust tires before and after classes. Sometimes, I had the good fortune of working the graveyard shift at the station

During the night shift, the big loads of fuel would come by truck and the driver would dump it into the underground tanks. One such evening, I visited with a driver who was dumping fresh fuel into our tanks. The thing that struck me as unusual was that the tanker had Unocal insignia all over it. I asked the driver why Unocal was being offloaded into a Mobil station. He smiled and grabbed a 5-gallon pail of powder and poured it into the underground tank. "There, now it's Mobil Super," he said.

He later explained to me that all fuels come from the same refinery and that the additives and anti-knock compounds were what differentiated the brands.

Having learned this, I started pumping regular old unleaded into my tank. Furthermore, I had no allegiance to a particular brand of fuel.

So why are people using super unleaded in their tanks? I suppose that it's good marketing. You can buy 87 octane, 89 or 91. What's the difference?

Most cars will run perfectly fine on 87 octane fuel. Moving up to more expensive grades is just a waste of money. Some cars are labeled "Premium Fuel Only." If your vehicle is labeled as such, then your super high compression 556 horsepower Cadillac CTS should probably get the good stuff.

Besides the above, why would you use high-octane gasoline? I wouldn't pump it unless there is a symptom to correct such as a detonation or spark knock (also known as a ping). Pinging occurs because combustion temps are too high. This can be caused by spark timing too far advanced, lack of a functioning EGR (exhaust gas recirc) system, engine overheat, too lean of a fuel mixture or really old fuel.

All of those symptoms can be corrected or repaired on your vehicle to eliminate a ping.

So why use the good stuff? I can't think of any reason.

John Salem is an L1-rated, ASE-certified master automobile technician and has owned Salem & Sons Auto in Kingman for more than 17 years.