My best with the 2.4 is 43 mpg on the highway.

 

I'll echo what many here have stated; driving habits are the biggest detail to fuel mileage.

But it's not exactly what many people think. My wife drives a lot slower than I do, but she averages 2 mpg LESS than I do. Why? I short shift(5 spd manual) and shift quickly, while she's a lazy shifter, and makes up for it by using more revs before shifting. But the biggest culprit, I firmly believe, is that she's a late braker, and I'm a 'coast up to the stop sigh/light braker. I can't stand to ride with her, as she just tootles along way slower than I'd be going, yet she's hard on the brakes at the last second for the light! Dammit, you see the light's red, toss it into neutral and glide up to the stop... In the very least, back off the throttle as you approach it. But no! She'll hold her speed steady until her foot has to get off the throttle and go to the brake pedal.

And I follow a LOT of drivers like her, too. I back-off, often gliding along in neutral, while the car(s) in front of me are pulling away, yet we all see the red light or stop sign, and I always catch right back up to them at the light a few seconds later. They have no clue that they are burning a lot more fuel than I am, yet we're all arriving at the same time, with the same exact average speed. Not to mention that my brakes will outlast theirs many times...

In short, driving slow isn't the whole answer to better mileage.

2007 LT, 2.4/5 spd man. Average 33 mpg(US)

 

I'm amazed that a 2.4 can average over 30 M.P.G off the highway.Mine gets about 31 at 70-75 m.p.h. and I can occasionally average a bit over 30 in mixed driving(that's kinda like hitting the big lottery,though).Mostly I average between 28 and 29 in the warm months and 24 to 26 in the cold months.I'm not complaining since I can average well above what the EPA suggests anyway.

 

It's shocking to see the difference in numbers you guys are getting. I use 93 and with mixed driving my 2010 2.4 5 speed manual I'm usually 31.5-33.5 combined in warmer months and in colder months I'm around 28-30 combined. The k&n really helped I think it gave close to 2 mpg difference for me here in NE Ohio. The worst mileage I get is on long trips going 70-75 I can't get an average over 26-27.5 but I've never got lower than 26 combined even before the k&n.

 

I've been generally getting between 24 and 27 combined, mostly highway mileage with the 2.4 and auto in my 2006, always running 93 octane. The 30+ at 70-75 that I've heard of doesn't even seem possible!

 

I just got my 07 LS in October and until this month I was just driving like I always have in the past. My average MPG's were showing 23.8 consitantly even after resets. My average speed shows 26mph. My driving is 100% city but the speed limits allow me to travel at highway speeds. I started attempting to get better milage and I am now averaging 30-31 MPG while still averaging 26mph. I use 87 octane and the car has 65k on it. I am traking my mpg in weekly durations. I am also expirimenting with various methods for getting better then this 31 mpg while driving 100% city.

 

I'm driving an 06 2 LT 2.4 with automatic, approximately 60K miles. I use 93 octane. A few months ago I took my car to a Chevy dealer and paid them to reflash/update the onboard computer systems. No other work was done.

I saw an immediate improvement of about 2 mpg in city and highway driving. These higher mpg results showed up in measurable tank-to-tank fill up calculations and on the DIC.

These are real world results - not theoretical. I was charged approximately 1 hour labor to perform the task. It was well worth the bucks expended. (PS - Using the "seat of my pants method," all other performance parameters improved, too.)

YMMV.

 

A gaussian graphic distribution of mpg on my 2.4 auto for 91K miles.


By oldlar at 2011-10-12

 

Some people feel the MPG rating on the HHR 2.4 is a GM lie, but I can tell you as a retired GM Tech who worked in the Road Load Simulator Lab (which is where we tested for CAFE ratings), the rating is accurate.

However, they are tested and rated at 55mph, NOT 70. Every vehicle is tested and rated at 55mph.

The boxy HHR has a lot more drag coefficient than other cars and hence the poor MPG at 65+ MPH. My 2007 HHR 2.4 sucks gas at 22 - 24 MPG at 70 MPH and steadily gets better as I reduce my average speed to 55.

Now, my old 2005 Vibe averaged 31 all the time on the expressway, 55, 60, 65, 70, 80, or 90 MPH. In fact I once drove it for one tank at 90MPH and it got 32MPG. Smaller motor, lighter car, and better drag coefficient.

The bottom line is we bought these HHR's either because we liked the looks, utility, comfort, or the price was right. I bought mine because I hated the Vibe, the HHR offered much better cargo space, and it looked cool too. (I wish Chevy made a decent station wagon again...) Too bad we didn't know about the economy issue...

 

I think I posted in another thread already, but between city and highway mixed, I'm just skimming under 30 with my 2LT right now. I have a pretty light right foot, though, and try to use physics when I can.
As was mentioned before, cruise speed isn't the only factor in saving fuel. Energy management would be a good term, and includes things like long coasting, easing off before cresting a hill, etc.