The 2.4 DOES recommend using premium for optimal performance. Check the owners manual. In my old 2LT, I could notice a slight perf increase with premium, but never noticed any mileage bump. The 2.2 is the only HHR motor not designed to take advantage of premium fuel.

 

I think my 2.2 does not require premium. If the 2.4 is designed to use it then your best mileage and performance will be with the gas it is designed for.

 

my dash dic thingy says 28.1. $3.11 more than reg gas would have costed for 15.575 gals. i will continue testing. if i cannot get more than 2mpg increase , i will not break even on the cost. also i did up the psi in my tires 39-40. the temp was 40 deg, and i did some 55mph where i ussually do 66 , at least 25miles. also found that 73mph is better than 72.

 

Hmmm my impression is exactly the opposite, excluding the huge loss when driving in snow. I had attributed it to the condensed gas and particularly the condense air (a.k.a Mother Nature's inter-cooler) for the improvement in cold weather. Again only when the roads are bare and the car warm (long trips) otherwise I agree, my winter mileage is absolutely terrible.

That said most of these reports were taken in the low 70 to high 60's (plus or minus a few degrees variance, day to day) - which to us poor Canadians is like summer.

 

I can't seem to get any sustained increase in MPG going from 87 to 93 octane. But there are so many variables with this crappy winter weather.

 

Howdy,

As a previous owner of a 2007 2.4L HHR LT (5 spd), the best gas mileage I ever achieved was during a trip to NYC/NJ/DC in Sept 2008.
7.2L / 100kms! Average speed was 105kmph roughly 65 mph. This was running 91 octane. On average, if I ran 91 octane, I got an extra 50-100 kms out of a tank depending on speed, and acceleration was not compromised. 87 or 89 just lagged under the gas pedal. I think that record trip on one tank came to 800kms+... somewhere in that number.

I picked up a GM Exec 2008 HHR SS (5spd) a couple of weeks ago (came from Michigan). I drove that home from Ottawa, averaging anywhere from 100-110kmph (roughly the same as the US trip) and achieved 8.1L / 100kms.
Now.. this being said, I did get stuck in traffic in Toronto and did enjoy throttling on to the highway over and over again, so I skewed my results.

During the trip, the HHR was reporting 7.x / 100 in the 'immediate' mileage menu option, so I do believe it's possible to get it down to 7.x if averaging 80-110kmph during the whole trip.

As to why the dealers kept telling people to run 87 / 89 in their tanks when the manuals said to use 91 only boils down to gas cost fear.
The guy who took my LT away looked a little nervous. I told him he'd get his savings back in more mileage and better power. I tell folks who use the 87/89 gas about my mileage record and they rethink their choice pretty quick.

Rob
Kitchener, ON, Canada