You did not mention if your 06 HHR was an automatic or a standard transmission. If your averaging 33 mpg with an automatic trans, your doing well. I have averaged 35 mpg with my 2.2 HHR with a standard trans, mostly highway driving. However 33 mpg is what I am averaging right now. I shift at 3000 rpm, use 87 octane fuel and drive no more than 5 mph over the posted limit on the highway.

 

Here is a variable that no one has considered..when you are on the road, take notice of traffic.. I found that if you experiment a bit with distance between you and the car in front your milage changes, that is are you catching the air from the vehicle in front?I'm not talking tailgating, that only works with big vehicles,, try it behind a motorhome one time, I did and pulled 33 DIC pulling a trailered bike with an SS. But I have noticed a mile or two just by varying the distance, this also depends on the type vehicle in front. Seems these cars are sensitive to airflow. Just like Nascar, clean air is good,,turbulant air slows ya down!
I see auto verses 5 spd all the time, the only real difference there is the final drive ratio, once the torq converter is locked up its one to one just like a clutch.Though in town its dependant on speed when it locks up.

 

Mine is a 2.2 auto, my mileage has dropped when it's below zero, only get about 28-29,.

 

That's excellent! When it's below 0, it's expected to have reduced mileage. It takes longer for the engine to get to operating temperature and it has to work harder to maintain it.

I just wish the "sweet spot" was a little closer to my Lumina. Not sure exactly what it was, but it was near 50-60 I do believe. Not that you guys care, but I got 40mpg in my Lumina going 60mph from Frankenmuth to Petoskey, which is about 200 miles. Pretty good for a 10 year old car!

 

mileage sucks here in the winter also. i have contributed it to the colder weather and driving less and only driving short distances. i hate the winter now. its waay too long this year

 

Ok, so today I was driving on the expressway with the cruise set at 60, and my mileage was only 33.

Shouldn't it be a little better than that at 60? It wasn't windy, really cold, or anything...

 

Ok, so I went on a little trip today on the expressway. Went down to Novi...

Anyways, I reset my MPG going down, and coming back, and I measured it ONLY when I was on the expressway...no on ramps, off ramps, or city driving.

Also, each way was 64 miles, for a total of obviously 128 miles.

Going down, I averaged 29.3 mpg, with the cruise set at 70 the whole 64 miles.

Coming back, I averaged 33.8mpg with the cruise set at 70 also, the whole 64 miles.

This averages out to 31.55mpg over 128 miles going a steady 70mph.

Not too bad I guess. I know some people claim to do better, but oh well. I'm sure in the summer when it's warmer it will be a little better. Not sure either why it was better coming home than going down...perhaps a headwind or something...who knows. At least it is a little better than the Lumina..even though it's only a few mpgs... I didn't buy the HHR for that anyways.

 

There may be several reasons why return trip was better. Just a little bit of an incline that you can not even notice makes a big difference in mileage. Much easier to push a car downhill than uphill. I use an altimeter on my mileage tests and it gives you some interesting information. You wuld be surprised to see what you think is a flat level road is really a slight incline. You can also see an immediate change in MPG on even small inclines. That road may have looked perfectly flat but had a 900 foot incline over the 68 miles?
Another reason is as the oil, transmission, bearings, and everything gets warmer they have less friction. When the car is cold it is automatically richened to run good but that hurts mileage. All things being equal the car will always get better mileage as it warms up like on your return trip.

Tire pressure can go up 4 degrees or so in that hundred miles and that is significant to mileage. As the tires get hotter the air pressure goes up which lowers rolling resistance.

Wind also makes a big difference in mileage. I have seen 10 MPG difference from headwind to tailwind. And a crosswind hurts significantly to. I watch closely flags along the highway to see if the wind is picking up and what direction.

Traffic makes a big difference in if they are "Blocking" the wind or if you have to slow down and accelerate again.

There are other variables that I just do not know what they are because I can do a test back to back same day, same direction and not get the same results????

Like on my race car we measure the Barametric pressure, wind, temperature, altimeter, tire pressure and I can tell you how fast that car will run. It is not so simple with these cars and it does not make much sense. When you know all of the variables and monitor them you should be able to reliably predict the results.
I know some of the variables but obviously not all.

 

Yeah, who knows what exactly was causing it, but I'm sure there were many things!

Like I said, I'm glad my average of the two was still better than the EPA estimate! I was just hoping that it would be at least 30....

I know there was more traffic on the way home, but they were all going at least 70 so I was able to use my cruise... Perhaps I was even drafting a little bit and didn't realize it...

 

you will see better when it gets warmer. when your engine is cold it uses more fuel to "choke" the system and your engine oil is thicker. ive reset my mpg cruising at 60 in the summer and seen it as high as 40. it went down as soon as some hills went up but i was impressed.