I recently read that cars that operate at high altitudes (Colorado) can use gasoline with 85 octnae versus the 87 that the manual recommends is this true? If so does using 87 hurt or help the engine? I regularly fill up at a gas station that sells 87 at the same price that most stations in town sell 85 for. It is only when I go out of town that I need to decide whether to pay more ($.10) for the 87.



Yes, it’s true because the thinner air means that your engine is compressing less air, and so in effect you have a lower compression engine that can run on lower octane.

Also, at least in my experience, often when there’s one or two stations in town whose regular is higher octane, that’s because it has a higher ethanol content, and so you might get better mileage and performance with the 85 octane.