WyoRock

Hey all. Have owned my 2015 Sierra SLE with Max Towing and 5.3L for all of 10 days. Still running on its first tank of gasoline, kindly filled by the dealer. I hate to start a controversy on my very first post by asking, but do you think it's okay for me to run on 85 octane? I know the manual says 87 minimum. Even the OP's thread title doesn't suggest 85 octane as an option. BUT... Where I live, the elevation is 6,100 feet. Everywhere in this region, regular gasoline is 85 octane. In past vehicles I've owned, dealerships have consistently told me it's fine to run 85 octane gas at high elevations, even though all the manuals state 87 minimum. I've done so in the past with no obvious issues. Many websites, including Pop Mechanics say it's okay to run 85 octane at high elevations. For instance at: http://www.popularmechanics.com/cars/how-to/a5308/4345737/?click=welcome-ad "I live in Arizona and use 87-octane regular. In Utah, Idaho and Nevada, stations were selling 85-octane as regular gas. This forced me to pay more for midgrade 87-octane. Is this the latest petroleum-industry scam to get more of our money? Will my car run okay on this bogus 85-octane regular? (PM Answer:) Octane is the ability of a fuel to resist knock, and high-compression engines tend to knock more. The obverse of that is that lower-compression engines can run on lower-octane gas. Air is thinner the higher above sea level you go. Less air going into the cylinders means less pressure at top dead center when things go bang. It's a lot like lowering the compression ratio in the engine, reducing the need for high octane. Cars will run just fine on lower-octane fuel when they're well above sea level--and all of those states are. Hopefully, by the time you get back down to denser air, you've burned off most of the low-octane stuff, and can refill the tank with higher-grade fuel." Anyway, what do you think? BTW, likin' my new truck!