Ask a Technician: Do I Need High-Octane Gas at High Altitudes?

Q. I've heard that you don't need high octane gas when you are at high altitudes, is this true?

A: You heard right. That’s actually true. Go to a gas station in Santa Fe, NM (7,260 feet elevation) or Denver, CO (5,280 feet) and you’ll notice a change at the pump. Gas stations at locations at or near sea-level sell 87 octane as their lowest grade fuel, but at higher elevations, you can find 85. What gives?

It’s all about compression. Your engine gets its energy from little explosions in the cylinders. Gas and air are mixed, compressed and a little spark, courtesy of your spark plug, ignites the concoction. The energy from that explosion is what gets your car moving. The key to a smooth running engine is to get the right compression ratio. If it’s off, you’ll get the dreaded knocking and pinging caused by the gas igniting due to compression instead of by spark.

The octane rating of a gas tells you how much compression it can handle before it spontaneously combusts. The higher the octane rating, the higher the compression ratio it can take. Regular gas is usually rated as 87 octane.

What does all this have to do with driving at elevation? Well, the air is thinner up there. A lower combustion pressure is required, and that means a lower octane rating is needed. It’s just a difference of a point or two (from 87 to 85), but every little bit helps. Keep reading our newsletter for more answers to your questions from the Sterling McCall Toyota service department.