SALT LAKE CITY — The roads will be packed this Thanksgiving holiday as AAA expects over 48 million Americans will be taking a road trip. In Utah, most gas stations sell 85-octane gasoline. But in most other states the minimum is 87-octane, 85 is not even an option. So, is using the 85 here — the cheapest grade — a bad idea for your car?

Insert your card, insert the nozzle, select the grade and squeeze the handle. Pumping gas is pretty routine for most of us. Perhaps, too routine for a KSL viewer who wrote to the KSL Investigators: “Every new vehicle that I’m aware of requires at least 87-octane fuel,” he writes. “Why does Utah continue to sell 85-octane unleaded gasoline?”

It is true: many owner’s manuals recommend their cars run on 87-octane, which means buying PLUS grade of gas here.
Does that make pumping the regular 85-octane bad for our cars?

 

 

“It’s mainly Colorado, Utah, Wyoming, Idaho, New Mexico, places that have higher elevations,” said Miland Kofford, program manager of the Weights and Measurements program for Utah’s Department of Agriculture and Food. “Altitude plays a big part in what octane does.”

Weights and Measurements are responsible for inspecting the thousands of pumps in the state to make sure the octane rating is right — among many other things. Kofford said many owners’ manuals are based on cars driving at sea level and Utah is far above sea level. He explained the air is less dense at Utah elevations than at lower altitudes, which means the engine draws in less air during combustion. Up here, 85-octane is just fine for most cars.

“You’re still getting that fuel in there, you just don’t have so much pressure,” Kofford said. “And so, it’s not forcing the engine to have preignition or combustion problems in the cylinder.”

He said using 85-octane at higher elevations naturally deters the pre-ignition or knock, that 87-octane does at lower elevations.

Kofford said while 85 is generally fine, he is a big believer in listening to your car. If runs and sounds better with the slightly higher octane, or gets better mileage — it will not hurt, it just costs more.

“They need to read their manual and decide for them as their car performs. Is it performing the way you want it to?”

Kofford added that drivers do need to check the manual to see specifically if it warns using anything less than 87-octane could void your car’s warranty. Then you’ll definitely want to gas up on the pricier PLUS grade. even in Utah’s mountain air.

Two more things you should know: If you’re driving a turbocharged car with a high-compression engine, you should always use the PREMIUM grade — no matter what elevation you’re at. And, mechanics tell us there is no benefit to running PREMIUM in a car that only needs REGULAR.