I disagree. I go 70-75 in my 2003 Grand Am (with the same 2.2L engine that's in the HHR, I might add, but I have the 5-spd) and I consistently get mid 30's on mostly highway and I've gotten as high as 39 on all highway. My wife's 2003 Impala LS (3.8L V6) gets 32-34 on our biannual (Early April and Late November) 1100-mile round trips to her parents house (speed limit 75 mph the whole way). I'm going by hand calculation and I use a similar method as Randy (except I count to 10 each time). I do not trust the DIC in my wife's Impala (my Grand Am doesn't even have one), it claims 35-36.

True, but over several tankfuls, it should average out. If by one measurement he measures too much fuel (e.g. the second pump lets the tank fill by an extra half gallon) resulting in a poor mpg calculation, his next fill up should show better gas mileage as a result (assuming similar driving conditions...and his tank isn't growing :)). The counting method is the only way to get even close to a good fuel use measurement.

 

I got better mileage from a '94 Buick Skylark with the 3.4L V6 (loved that car). One of the reasons I purchased HHR is for mileage. I do recomend running at least 90 octane in the 2.4 as I have seen a drop off when running less in ND.

As for all of the suggestions, most are great, but I think the OP is going to have to resolve this with the dealer. It reads like something is wrong with his car. Good luck

 

*sigh*

On my last trip this weekend, I was at 32 MPG averaging 65 MPH through hill country on about half of the trip over 362 miles. Most of the time when I hit 70 MPH, mileage starts to fall below 30 MPG.

I don't know what's wrong with you or your car, but I'm tired of arguing about it. I highly doubt anything is actually wrong with the car except for user error. My advice would be to rent another similarly equipped HHR and repeat your tests. If you're not satisfied with the results after that, go buy your Prius.

 

Have you tried changing gas brands? If your gas is high in alcohol it will give you a much lower mpg.

I see a 2-3 mpg difference here in the bay area from the winter blend to the summer blend gas.

 

I've also seen 30+MPG on the highway in the last few sedans we've owned. Right around 30MPG in our old 3.1L Grand-Prix at 75MPH, and 32-34MPG on my old 4-cyl 5-speed Accord at 75-80MPH. Aerodynamic sedans can get 30 or higher on the highway in real-life use, but flying bricks like the HHR and most crossover SUVs will just encounter lots of wind resistance at higher speeds so their economy suffers.

 

Dear Lord Almighty-I read all these posts. RTH has a legit gripe, after all its his car. Mine doesnt get nearly what most of you are claiming. Its brand new so I will wait and see after its broke in. My driving is ALL city, more flat than not, an ocassional romp just cuz I can, 36 in the tires and I now use premium fuel as I like the way the car responds. If I can get upwards of 20 Im gonna be a happy camper.

 

20MPG in all-city driving is about what my car got when my wife drove and we lived at our old place. That was an improvement of ~20% over our previous car, a Grand Prix 3.1L (17MPG in town). Seems plenty reasonable to me.

 

Thanks! I'm gonna look into this. I have new respect for the a-holes in my town who drive 20 liter duallies to work every day. I always thought they were getting 5 MPG.

I drive city only & get about 23. I vary between "old man" cruising, and lead footing it (when my road rage kicks in).

 

I hate to get into comments on mileage, since YMMV.

But, some to add....

Higher octane gas has absolutely no more potential power than regular, since they all have the same BTU potential. High octane fuels have the same BTU potential, but only have slower flame propogation rates, IOW, burn slower. BUT.... The ECM programming deals with this.... more later...

The more commonly available E10 (90% gas/10% ethanol) will lose both power and mileage, since ethanol has 80% of the BTU content than gas and (do the math, folks!), as a result of E10 you WILL get about 2% loss in BOTH power and mileage... fact!

As far as the effects of what octane you decide to buy.... First, GM "recommends", not mandates, 91. The ECM will deal with the normal ranges available, and is programmed to the "lowest common denominator".

What will happen.... The E67 ECM on the 2.4 has two tables, High Octane and Low Octane. They are base upon timing parameters determined by cylinder air mass and RPMs at any load and engine speed points. What happens is that, should any knock be detected, the ECM is programmed via algorithims, to compute what is known as the "Knock Learn Factor"(KLF). To put it simply, the ECM will "learn" up or down to determine the spark advance between the two tables based upon the knock detected. IOW, it will compute that "sweet spot" to find the optimum spark advance based upon the fuel used.

Want to use 87? You will lose both power and mileage, since the engine will operate at lower ignition advance to avoid detonation. Higher octane will allow more advanced spark. That will result in higher power and MPG levels. Whether that makes an octane choice better is hard to determine as a bottom line, let alone the variables in normal driving.

For city mileage, what about how many red lights or stop signs per distance travelled? How much time at lights? (0 MPG) For highway, how hilly? What about the current winds? (behind or against?)

What about the individual's driving habits? Of course, everyone thinks they are an "expert" driver. When not on cruise, how steady are you on the gas?

All that said.... I've been tuning the HHR for over a year now and know what happens. I can consistently get about 35+ MPG at a typical 70 MPH average. Mine is tuned for 93 octane.

To the OP.... get your car checked by a competent tech!! If you tire gage is accurate and you can drive smoothly, etc., something IS wrong!

 

Nice and accurate explanation, JOE