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post #1 of 32 (permalink) Old 06-01-2013, 07:55 PM Thread Starter
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Another Bad Mpg Thread.

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.


Last edited by stickx911; 06-01-2013 at 08:08 PM.
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post #2 of 32 (permalink) Old 06-01-2013, 08:27 PM
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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.

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post #3 of 32 (permalink) Old 06-08-2013, 08:44 PM
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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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post #4 of 32 (permalink) Old 06-08-2013, 10:10 PM Thread Starter
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Quote:
Originally Posted by 5t3alth View Post
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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post #5 of 32 (permalink) Old 06-08-2013, 10:20 PM
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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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post #6 of 32 (permalink) Old 06-08-2013, 11:38 PM
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Oil, tire pressure, air filter, plugs?


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post #7 of 32 (permalink) Old 06-09-2013, 05:58 AM
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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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post #8 of 32 (permalink) Old 06-11-2013, 08:00 PM
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28 depending on how much city isn't too bad

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post #9 of 32 (permalink) Old 06-12-2013, 04:13 AM
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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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post #10 of 32 (permalink) Old 06-12-2013, 09:26 AM Thread Starter
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Quote:
Originally Posted by money_man View Post
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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