The manual says never to use Below 87 octane. 87 octane is acceptable, but may reduce performance.

 

Went on the mother of road trips Michigan to Houston, TX from there to Mrytle Beach, SC and then back to Michigan. With side trips over 4,000 miles. HHR drove great and got between 29.8 and 32.4 depending on weather and Hills. Not bad at all. My sitbones are hurting.

 

I'm sure it's 91 because some states don't have anything over. Even the SS with the tune can run on 91.

I people are intent on wasting money. To each their own.

 

LOL, my sit bones hurt after 250 miless, let alone 4000

 

Im very disappointed in my fuel mileage with my new 2008 2LT HHR. It has allmost 3k on it now,I changed the oil over to Mobile 1 @ about 950 miles, have a light foot and my DIC says im getting combined 20 mpg.

Sucks, Im going to take her back into the dealership and have her checked out. Other than my Mileage, I LOVE this baby.

Sure turns ALOT of heads

 

took my '07 on it's first road trip, a weeks worth of around town prior and DIC indicated 27.9 while math came out to 29.55 mpg. Return trip with 3 days around town DIC at 28.0 and calculated fill up at 30.15 mpg, at 72 mph with A/C on

 

You might want to take a hard look at your commute....
Check out this thread..https://www.chevyhhr.net/forums/fuel-economy-hypermiling-47/commuting-choices-16818/
While doing this, I kinda confirmed there is a sweet spot for mileage. 40-45mph when the torque converter locks up, the rpms drop to about 1500. If you can keep it there, you'll get probably your best mileage. Good Luck - the dealer probably "won't find anything wrong"

 

Tell us more about the length of your trips each, octane, city vs highway, mileage on longer trips, speeds, auto/manual. Elevation etc. 20mpg is ABSURDLY low. As I told another person with the exact same complaint. Either you hhr is broke, or you driving is. No offense, you may just take really short trips, and always startup cold (the reason for the other members poor mileage). Log a week or so of each trip you make.

I'm pissed right now that my overal mileage has dropped to 34.4mpg 70/30 hhy/city.

Let me know.

 

I just went outside to check the DIC.

It said average MPG was 21.5 and my average speed was 25 mph. This is for the last 950 miles that we have driven since we re-set the trip OD.

I understand about the sweet spot for optimal milage, but im NOT going to drive 50 mph on a 70 mph Highway. Thats just NOT going to happen.

Octane is 89
Auto trans
2.4 engine
Reside in Michigan

 

my last tank was almost all freeway and I went 512 miles and put in 15.17 gallons thats 33.75 mpg and about 80-85% freeway with some stop and go with some hypermilling i try to drive 60-65 and i set the cruse control as often as possible. I do have a pretty good hill climbing to and from each morning I drivr over the Altamont pass here in the bay area my milage drops every day climbing it then if traffic allows I drop in to neutral and coast the down hill to get it back up (down hill is like free mileage to me) and I also take some back roads less stop and go except a few stop signs but I can set the CC at 55-60.This is with 87 Octain. My DIC said 32MPG it is usually about 1 to 1.5 mpg under which is fine with me better under then over