We got a note from a reader who’d recently been on a road trip out West. Piloting his pickup with a V-10 engine, towing a travel trailer, he started to encounter severe engine knocking. He got seriously concerned, thinking he’d developed engine problems. Happily, “the light came on,” and it wasn’t that dratted “check engine light” either – it was the one upstairs between the ears.
Our reader encountered the problem while chasing around in Arizona in the relatively low, 2,000 foot altitude area. However, his last fuel fill-up had been in Albuquerque, New Mexico, elevation pushing nearly 6,000 feet. If you’re having an “Aha!” moment, good for you. Fuel stations in some high altitude areas (particularly Colorado) often sell “regular” grade gas with an octane rating of 85 – not what ‘most of us’ buy, the 87 grade. What’s the deal?
Octane ratings are a measure of gasoline to resist engine knocking. The argument is made that at high altitude, where the air is “thinner,” there is less likelihood of engine knock. So, sell the customer 85 octane fuel (for the price equivalent of what you’d pay for 87 octane elsewhere) and let ’em go. Interestingly, Colorado’s own Legislative Council says that the “85 is OK at high altitude” argument is bogus, particularly for older (pre-1984) engines, but they’re still selling the lower-test gasoline throughout the state.
So where does that leave the “gasser” RVer who plans on checking out some of those high-altitude states? Well, if your engine is younger, while driving around the high altitude areas on the 85 octane level fuel, you “should be” good to go. Motorist group AAA recommends you ask your manufacturer or trusted mechanic, though. However, when you take your rig ‘down the hill’ to a lower elevation, “thicker air” area, you may begin to notice what our reader did – serious engine knock.
What’s to be done? If you’re filling the tank and figuring you’ll be using it when you head out of the high country, you may want to spend extra bucks for the mid-grade, higher octane fuel. Burning higher grade than your engine specs require won’t hurt the power train, it’s just going to cost you more. Or you could try and skimp it, pump in enough of the 85 octane stuff to get you back down in altitude, then hit the first pumps you can find that sell the “real” 87 octane stuff.