How are you getting a 25mph average driving 70 mph? Seems like you are doing alot of around town driving and 21.5 isnt bad for your average speed.
got me a little confused

 

Yesterday I drove across Florida and back 233 miles and filled up once I got home, 6.6 gallons... 35 mpg, DIC said 31? Granted most of the drive was ~55 except a 60 mile stretch on I-4 where I was the slow one at 70-75 mph.

 

I thought mine was broke. I get CRAP mileage but found out why. My commute is 2 miles to work and back so this plus after work errands work out to be about 10 miles a day M-F. It's all hills, I rarely get above 30-35 MPH so Im running around in 3rd gear most of the time. My new record LOW miles per tank was 186 and 13.73 MPG. This particular low was 2 days of driving like a fuggin madman.When I change my route and avoid the damn hills, when I can I make sure to get the TC locked up and back down to speed limit and the mileage goes up significantly. The best Ive gotten was 20MPG and this was 95% city driving, all below 40 MPH with a couple of 40 mile trips on the freeway. No cold start driving, I live in Cali and 2 minutes after start, the temp goes up. No need to warm up.

When I get on the freeway, I go 60-65 MPH and the DIC says 28-30MPG so I know its not broke. What I would really like to do is lower the speed that the TC locks up in. Ive looked into this and it seems that at least for now, nothing is available to modify the factory calibration of a 2.4 auto. I also noticed a black tailpipe but failed to disclose that I was using Lucas fuel treatment waaaay too often. I have since stopped this.

As mentioned in this thread, when you can drive in lock up mode, you get killer city mileage. Even the folks that have bumper to bumper commutes will get good mileage because they're RPMs' are still low. Its the running in 3rd/2500-3000 RPM's that will kill the mileage. I use 87 octane. Ive had it in the dealer twice and they find nothing wrong. No codes found, its my driving that's the cause.

 

Your average speed is very low. Mine is 37mph on this tank. Realize i drive slower than anyone not PARKED. So you must be doing 75%+ city driving. That is the only way to get such a low avg speed. The sweet spot is 40-41mpg, this is obtained at 55ish mph. Trust me, few here get 40-41mpg, and if they do, they are doing it at 55ish mpg on a flat highway , after sufficent warm up, with little interference (wind, rain, extreme temps..etc). In michigan the speeds are 5-10mph higher then in Cleveland. So you should shoot for 36mpg at 60mph. Or 34mpg at 65. At 70mphif you can manage anything over 30 your doing okay.

IMPORTANT.

These are numbers that you should see over thousands of miles. Not some TOOL quoting a one-time-trip.

I do 55ish on the highway, and the limit in the city. At 75% highway or less, I am averaging 37mph.

Your problem is your avg speed.
You should log a day or two of your typical drives and reset your odo-b,avg spd, avg mpg and see what happens.

 

You must not have reset your dic avg mpg at the time of the fill up. There is NO WAY it is off by that much. I have never seen it of by more than 0.25mpg in my hhr ss. I track my mileage like a fanatic, and you DIC is DEAD ON.

 

Yeah in my "Absurd Mileage" thread (sorry for being lazy an not updating) i do take a few trips on purpose to the drive thru, house shopping, and in a monsoon like rain (Browns pre season opener), just to show what these things can do to mileage. It rained so hard last Thursday that I LOOKED FOR MOSES!!!!!

I also lost my hypermiling cool and put the SMACK DOWN on a late 90's turbo eclispe (pristine condition). You know the one, women loved it's cutesy curves, the dudes all wanted the awd turbo version. Anyway, I had to represent the LNF. He began driving recklessly to keep up with me in heavy traffic. So i slowed back down to 55 and let him pass me after leaving him in the dust 3 seperate times at 90+.

The point is that my mpg for that specific trip with only 5 miles of 12.4 miles driving like Fast n Furious dropped to 28.2, I have never seen mileage below 35 all the other times i drove it. So 90% of the mileage problems here are between the steering wheel and the seat.

later

 

Nope I reset it every time. I'm anal about tracking gas milage since owning cars with faulty gas guages and running out of gas a few times. I have an EXCEL spread sheet tracking the mileage of the HHR since new. The running average mileage is 30.4 mpg for nearly 36K miles. The tank to tank varies from a low of 25 to a high of 36.

Does anyone have information on how the DIC calculates the milage figure?

 

Im coming off of a 2003 Saturn Ion 3 and my mileage at 80mph on the Expressway was about 31 mph with the 2.3 Ecotec engine in it.

I certainly wont travel that fast in my 2008 HHR, but at 73 MPH with the cruise control set, I sure would expect to get 27-28 MPG.

Its just not happening. I think when I take a quick trip to Detriot this Wednesday, I'll go up to a tank of 91 Octane and see what happens.

Bill

 

I recently made a 500 mile trip from IL to MI - nice weather all the way. I have the 2.4 automatic and was using 93 octane fuel. The first several hours I had the cruise set at 60 and the DIC showed the average mileage had worked its way up to 34.0 mpg. The last few hours I bumped the speed to 70 and the average mpg shown on the DIC dropped 2.5+ mpg.

Now I know the DIC numbers are not necessarily accurate, but they are useful to show trends. My HHR seems to show "significant" decreases in mileage above 60, more than I would have anticipated.

 

You guys are certainly correct, most of my driving is definately around town commutes.