weird i know someone with a 2.4 and on the gas cap has a sticker that says 87..maybe depends on year?

 

Maybe so, my gas cap has an icon, a pic of a book with an "i which means go check the manual...no THAT is weird

 

Since about my second or third fill up I've been using Shell 93 rating gas.I do remember the mileage picking up when I switched to premium but that could have also been the engine breaking in.
I average about 27 m.p.g. in the summer,23-24 in the winter.The highway mileage is my only real disappointment.I've never gotten over 31 on a long highway trip.I've put that down to the HHR being a bit of a brick and the fairly low final drive ratio with the 5 speed manual trans.

 

The 2.4L is rated to go 28 mpg on the highway. Anything past that is welcoming

 

I usually always put in 87 (I'm cheap)...but this past week I decided to put in a tank of 93 because I haven't ran any in a long time. OMG what a difference already. I'm averaging 28 mpg in the city on my 3rd day...generally on day 3 I'm at 22-23. Also the throttle response seems a little tighter (probably my imagination). I think from here on out I'll stick to 93.

 

vinnyac 06 HHR 2LT Loaded 140,000 miles. Hi everyone, just wanted to say, I use hi-test gas instead of regular because less engine knock, less engine noise, runs better on premium fuel. Engine has no mods. the only add on was a power chip hook to the mass air control, two wire hook up. The chip gets about 1-2 miles more in the city 22=23 and 30=33 on the highway. It also makes the auto trans shift better. As for the cost of gas, regular vs premium, at 20 cents more a gallon for premium, that's $3.20 a tank full. Why be cheap, you get better over all performance. If 3 bucks is to much for you, what can I say?

 

Have been running 87 since I've had her and getting 30-31 highway. 08 LT panel 2.4 stock.

 

Vinnyac--where do you get premium for .20 a gal. It's 40- 55 cents a gal. here in IL.

 

I've found it to be $.30 over 87 in most areas

 

It's hit or miss here. Some places midgrade and premium are only $.10 increments, I've seen a couple places where premium is as much as $1 over regular. But most places I've seen back home(lived in Michigan for 12 years) was $.20 over for premium.