I have a 2009 HHR with the 2.2L engine. According to my owner's manual the minimum recommended unleaded gasoline is 87 octane. However here in Colorado, our regular unleaded gasoline is 85 octane. 87 octane is our mid-grade. I know that's because of our higher altitude, but I am just wondering, will using 85 octane void my warranty? My dealership said it's fine to use, but still... Any Colorado HHR owners out there have any problems running their HHR's on 85 octane?

bum, I can assure you every 2.2 Ecotec in Colorado is running on 85. Remember, you lose 4% of atmosphere for every 1,000 feet of altitude. At sea level you are a lot closer to knock with 87 than you are with 85 in Denver.

Thanks! Good to know that it won't hurt the engine at this altitude :)

now i wonder... what happens if i drive down to sea level on a tank of 85?

you may have some knock issues, but the computer will compensate somewhat with timing.

You probably can't get to sea level, or anywhere near it, from Colorado on a single tank of gas.

You probably can't get to sea level, or anywhere near it, from Colorado on a single tank of gas.

Those pulling HHRs behind their motorhomes as dinghy vehicles conceivably can.

The ECU will just pull timing to compensate. You will lose power, but that's pretty much it.

Yes that is 100% correct that your car will work fine on 85 octane at this altitude. You really don't even need high octane unless you are standing on the gas. Driving to the SEMA show last November, I even put 85 in my Corvette knowing that I wasn't going to stand on it or anything, and it requires 93 according to the owners manual. That would be a huge difference, but even dinghy towing behind an RV, there isn't a huge difference between 85 and 87 so I doubt the computer would even have to compensate, although it would if needed.

I have used 85 in every tank of gas in my HHR. that has only been 3000 miles, and I haven't left the state, but I have had no issues.

I know this is not the case with every vehicle though. My previous car was a 96 saab 9000 turbo, required 87, put one tank of 85 in and it felt like the gas pedal broke... plus mileage was horrible. That old computer just could not handle it.

Has anyone noticed a decrease in MPG on 85? i am averaging about 25 mpg mixed city and highway, but have nothing to compare it to. Would 87 help?

You probably can't get to sea level, or anywhere near it, from Colorado on a single tank of gas.

Actually, going west out of Denver you can get below 2,000 ft altitude before a refuel somewhere in Kansas. That said, I have never had a fuel issue on that drive with any car I've had in the 20 years I've been in the Denver metro and driving I-70 east into Oklahoma. I do tend to get "real" fuel as soon as I use up the altitude mix going east, and try to fill up near the Colorado border to have some non-oxygenated fuel for the final leg home (it gets better mileage).