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Discussion Starter #1 (Edited)
In my 08 base cobalt I would average 28mpg with my driving. In my g5gt I'm only getting around 23.

Suspects (symptoms),

Timing in motor - there is a faint, but not alarming tick in the motor as it runs.
bad wheel bearing - slight sound, but if it is to come, it's not too bad yet. I also get a little pull at slow speeds, so it's there, but I don't know if it's my mpg issue.
Bad calliper - also that pull could be from a sticky calliper.

It has 80k miles on the motor and I've only put 2k on myself, it had been a rental/fleet for 20k and driven my a teenage girl for 40k...lol

Spark plugs need to be changed I'm sure.

Just making sure I'm on the right track here and looking to see if there is anything else I should keep an eye on.

Check 02 sensors? or?
I don't have a lot of knowledge on this subject so I wanted to seek an outside opinion.
 

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Next time you drive the car, try putting it neutral at lets say 30mph and let it come to a stop on its own. Then get out and check the rotors for heat. If you coast to a stop without applying the brakes your rotors should be cold to the touch. Be careful if one of them is red don't touch it.

"Not responsible for index fingertip blister"
 

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In your base model cobalt did you change out plugs or still OEM? Should be AC Delco Iridiums in there for 100k maintenance and that's the average lifespan of them. Don't worry about 02 sensors if you don't have a CEL on. Your mpg could be from fuel leaking recall. Do you floor the accelerator pedal a lot? City based driving only? I mean by driving from stop light to stop light only and short trips would cause your mpg to decrease. Most of your fuel is consumed during startup and cold engine temps. It should take roughly 4 minutes for engine to heat up to 190-200 degrees (normal engine temp) and your 02 sensors are still in open loop trying to achieve closed loop. Your first 15 miles roughly are the worst for your vehicle on mpg, it gets better as you drive and coast/cruise.

Coby7 has some good info as well, your brakes could be slowing you down too if warped or heat spots are indicated.
 

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Discussion Starter #4
In your base model cobalt did you change out plugs or still OEM? Should be AC Delco Iridiums in there for 100k maintenance and that's the average lifespan of them. Don't worry about 02 sensors if you don't have a CEL on. Your mpg could be from fuel leaking recall. Do you floor the accelerator pedal a lot? City based driving only? I mean by driving from stop light to stop light only and short trips would cause your mpg to decrease. Most of your fuel is consumed during startup and cold engine temps. It should take roughly 4 minutes for engine to heat up to 190-200 degrees (normal engine temp) and your 02 sensors are still in open loop trying to achieve closed loop. Your first 15 miles roughly are the worst for your vehicle on mpg, it gets better as you drive and coast/cruise.

Coby7 has some good info as well, your brakes could be slowing you down too if warped or heat spots are indicated.
Stock plugs, and I didn't know about the recall, so I will look into that! thanks!
 

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Could be a combination of things. Some other things to consider: air filter, alignment/wheel balance, tire pressure, dirty injectors, driving habits? My first thought would be O2 sensors though.
 

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Oil, tire pressure, air filter, plugs?
 

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My cobalt only had 116k km on it when I checked the plugs and mine were shot. The gaps were way off and the plug itself was wore out. GM might claim they're good for 160k km but I would check yours. I would then check(by check I normally mean change because its a $10 item) the air filter, and I would change the fuel filter.

If you do have a caliper sticking than just going for a short drive and back you will notice a difference in heat, but if the car is pulling in one direction you could always just jack the front up and check which wheel is harder to spin. Once you find the harder wheel don't assume its the caliper just yet. Now unbolt the caliper and try pushing the piston back, if it doesn't go back try opening the bleeder screw and see if it goes back fine then. If it goes back fine when you open the bleeder screw then its not your caliper and probably the flex line is being blocked off with rust.
 

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28 depending on how much city isn't too bad
 

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the g5gt should be harder on fuel anyway since its the 2.4 compared to the 2.2. Its also the GT version so its going to weigh more than his base cobalt did. Then like i944scania said depending on the amount of city driving it would be lower.
 

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Discussion Starter #10
the g5gt should be harder on fuel anyway since its the 2.4 compared to the 2.2. Its also the GT version so its going to weigh more than his base cobalt did. Then like i944scania said depending on the amount of city driving it would be lower.
I figured it would be lower than my base, but this is more significant than I expected. I figured I'd go from 28 to maybe 25, but 22 or 23, to me seems to be a little low. Maybe I'm just being picky. Again, same driving habits from one vs the other. Even my freeway driving is down to maybe 31 instead of a 35+ avg I'd get before. Maybe I'm wrong, it could just be the gt I just wanted to make sure I wasn't missing anything. I didn't expect the extra .2 to really make a big difference.
 

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did you end up checking the gap on your plugs?
 

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Maybe you drive like a maniac! I get around 28 in mine, but I spend a lot more time having fun than actually driving like a normal person!
 

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Maybe you should actually calculate it one time. Run a full tank of gas for however long that would last you and do the math. I dont always trust the DIC
 

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Cant use your average. Fill it til it clicks off, then burn that tank, and then fill it back up til it clicks off. Now take your miles and divide by the gallons you put in. That number will be your actually fuel mileage of that tank.
 

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Discussion Starter #17
Changed plugs, front hubs,filers, tune, pads and rotors (no major signs of a bad caliper), and im still in the rough. <30 all freeway. Checked mileage to the dic and they were not perfect, but the dic showed a little more optimistic numbers than reality :(

Fuel filter changing this week, and probably o2 soon (theyre more expensive and much harder to change)
 

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dont forget use only a o2 sensor from the dealer. AC Delco brand, any others will give you problems
 

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i'm using a denso on my upstream O2 and its been good so far so i would also recommend that
 

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pfff i declare!!!!
 
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