We almost never use remote start, and we do not leave the car running to warm it up. It stays in our garage... so there's no need, and no opportunity.

Again... how can you screw up hand calc'ed mileage?

As for the Silverado... you can doubt it, but it's true. And... there are lots of others out on The Diesel Place (www.dieselplace.com) who get comparable or better mileage. Has everything to do with the Duramax diesel engine and aftermarket tuning. It flies in the face of all of my experiences with larger trucks too... but all of my previous experiences were with gas-burning engines.

 

The DIC in our 07 is pretty close to actual mileage, easily with in 1 mpg. How do you calculate your mileage? How many miles do you get on a tank?

 

quidquid latine dictum sit, altum viditur

Okay, Mr. "Man, this mileage sux"

Having an M.S. in Mathematics does not make you an engineer, which is obvious by your failure to consider other factors related to the mileage issues you're experiencing.

In other words, whether I dumb it down or sound like a smart aleck with clever latin phrases copied from Google, you're still complaining like a whining child. Your comparisons to a full-size diesel truck and a hybrid-electric car are silly and ridiculous. The HHR is rated at EPA mileage at 55 MPH. When you load the car up and start driving through hill country going 70 MPH in cold weather, your mileage is going to take a hit no matter what you're driving. Add a bug deflector to the mix and you've shaved another 2-5 MPG for the shiny piece of smoked polycarbonate.

Out of curiosity, how far did you drive after topping off the tank, and how many gallons did you have to put in after you reached your destination?

 

Actually it is easy to screw up the math by hand. Filling a gas tank to the same level each time is quite a trick. I have noticed that even a small incline at the station will stop the filler at 3/4 tank depending on how the car is positioned. Gas mileage by hand should be done over very long distances, such as increments of three tank full. Even then the average may be off some. This is simple statistics. I have been tracking mileage in my cars for over 30 years and it can be meaningful but one must be careful not to make much of a single calculation for a single tankful.

I have found the electronic devices installed by manufactors to be quite accurate and trust them far more then simple calculations.

All said, some people and screw up driving to the extent they could not get decent mileage from a bicycle. Getting good gas mileage is a matter of good habits. And yes, I have driven professionally. For the past ten years I commuted to work 500 miles one way every other week. I estimate I drove the distance to the moon and half way back in that job. I could depend on getting 40 mpg out of a Dodge Avenger, 33 from a Chrysler Concorde, 36 from a Focus and 31 from a PT Cruiser. However, my new HHR works hard to give 31 on the road and I am disappointed in that. It only has 2000 miles and I have noticed steady increase in mileage up to the 15000 mark then leveling off. So I may yet do better. RTH, you may just be one of those who expect too much. The point here is that one or two individual tankful just is not enough evidence.

 

Well... fine. Obviously you all are sitting in the back of my car and watching how I drive, how much gas I put in my car, all the time evaluating the condition and "hilliness" of the roads... etc.

You all may not like the numbers I'm sharing with you, but I think I know how to apply engineering techniques to the evaluation of something like fuel economy. Cold temps? If you consider 45-65 degrees F cold, then yes... I drove in the cold. Hilly terrain? When compared to the plains of the southwest... yes. But hilly? Not really. Certainly nothing like the land of the "Show Me State". Loaded down? One passenger, and one suitcase. If you call that loaded down, then I guess I was loaded down.

Filling the tank to a consistent fill level? I fill until the pump kicks off. I then count to 5, then squeeze the pump handle again until the pump kicks off. I then count to 5 again, then squeeze the pump handle again until the pump kicks off. Then I quit. Is it precisely the same station-to-station? No. But I'd be happy for someone to tell me what a better procedure is that results in a more consistent fill level.

When checking strictly highway mileage, I make sure to fill up as close to the highway on both ends of the test. I always accelerate carefully to avoid unnecessary gas usage while coming up to speed, and I use cruise control.

So... what scientific process did you employ to ascertain that a bug deflector eats 2-5 mpg? Are there some authoritative studies you are citing, or did you simply pull the numbers out of your [choose an appropriate orifice]. BTW, we keep the car clean and waxed, and we do not have a roof rack.

I drove 146 miles after filling the tank as described above. When I made it home, I put 6.53 gallons of gas in it. How would you calculate the mileage?

Is one tank a trend? Certainly not. But this is fairly consistent (within 1-2 mpg) of our average mileage for the past 8 months, with only 2-3 tanks ever approaching 25-26 mpg... all hand calc'ed. The absolute best single tank we've ever seen was 27 mpg this last fall - one passenger, two large suitcases, early October, very warm (75-95 degrees), and 70 -75 mph in the hills of North Carolina.

If you don't believe the numbers - that's fine; I don't really care. If you feel compelled to cast dispersions, name call, and act childish... that's fine too. But whether or not you like it, I believe this car has something wrong with it, which is why I asked for ideas on what might be wrong. I've gotten a few good suggestions - dragging brakes, bad spark plugs, faulty injectors, tire pressure, aerodynamics, and premium gas.

If they find anything when I take it in tomorrow, I'll let you all know.

 

Bug deflectors are known mileage reducers. They are designed to increase drag and decrease aerodynamic efficiency in order to do their job--deflecting bugs! They aren't there to keep the edge of the hood pretty...

Any car that's traveling over 65 MPH is going to have trouble hitting 30 MPG. Vehicles marketed in North America simply don't have the gearing to maintain those speeds with any kind of efficiency. Also, keep in mind that you're never going to get a consistent fill-up between two gas pumps--even with your weird "count to five" method.

Another question--what do you have your HVAC controls set on? If you leave it in defrost mode the A/C compressor is constantly engaged and THAT will definitely eat the mileage too.

 

Here are some tips and things to look at to improve your mpg and it is a government site http://www.fueleconomy.gov/feg/drive.shtml

 

Same with recirculating air option that will turn on the A/C compressor too.

 

So... do you just not believe all of the people out here that claim 27-35 mpg's in their HHR's running 70 mph or better? I'm beginning to not believe them, though I am willing to consider the possibility that my car has something wrong with it. I don't buy the idea that everyone else is driving on flat-as-pancake roads and have somehow perfected their driving techniques.

You have a better suggested method? Do tell. Weird or not... one of the basic tenets of repeatability is consistent process.

HVAC controls were set to vent... and not on constant recirculate. Again... we're not talking just one tank of gas; we're talking about 8 months worth of what I consider lousy gas mileage.

 

Randy,
Have you tried going to 91+ octane yet? I know others are saying it doesn't seem to matter for them, but every state has different standards for fuel (some states have many different standards by region) and different additives. I'm pretty sure the 2.4 is tuned for premium. It may be that your computer is retarding the spark timing because of the lower octane. Are other people's cars getting decent mileage in your area? Maybe your area just has highly oxygenated fuel (particularly in winter).

Have you had your fuel pressure checked? A faulty pump or regulator could be resulting in poor fuel atomization.

Is your tire guage accurate?