hmmm. I know how the dealership can be, when addressing problems that are not easy to solve. The first thing out of their mouth is always, "it's your driving style" or "they're all like that" or "it's characteristic of the vehicle."
i went through a similar nightmare with honda a couple years back. But i stayed on them with a vengeance until they corrected every single problem.
As long as it's not to your liking, keep bringing it back. I assume that you are under warranty??
Unfortunately, you may have to do a little leg work yourself, to get them headed in the right direction.
Let's check some things. You have the 3.5 v6 right? yes
does your radio have the trip computer included? yes
what does the display show your avg mpg @ right now? 18.9ltrs per k
using the instant mpg, track what your mpg is at various (steady) speeds.
At a steady 35mph, 50mph, 60mph, 70mph? I've always been very impressed with the 3.5's highway economy. At 65 you should see, atleast 26mpg on the display. 28-30mpg is what i've always seen indicated at those speeds. i will try this
in spirited, city driving. I *always* get 17 or 18mpg indicated by the trip computer. This is on *every* recent gm 3.5, 3.8, 3.9v6 i've driven. If i am more sparing with the throttle, i may see 19mpg indicated for city driving.
So i can see how city mpg could be a little low. But on the highway, these engines, with their healthy low end torque and tall gearing, really shine (rarely falling below 26 mpg avg).
These are things you may have to do (but your dealer should have already):
Jack up each wheel and make sure it spins freely, without drag.
Check your tire pressure.
I'd replace the fuel filter.
Run a quality fuel system treatment through the gas tank. i have not done any of these things to date, but i will try and do by early next week and advise
did this car ever get good mileage? i cannot say, i bought the car with 20,000 k on it and i also owned a f-150 8cyl, i used to drive both. So when i got in one and it needed gas i put it in. But never tracking it. I sold my f-150 and am only driving my g6 and this is the reason i am noticing it now. I also must say that i owned my truck for 6 yrs and only used that for a period of 4 yrs and got way better consumption in it. Interesting fact is i drove my truck the same way that i drive my car. Mostly in town. give it a good listen for any strange sounds from the engine and tranny. Both should be relatively smooth. sounds normal
you say the dealer got 7.8lpk? Whoah! I just converted that... 30.1 mpg!! No way. In the city? That's just bs, for sure. yes... They claimed that it was considered city driving... I told them they were full of crapola... They are not driving it the way that i am and that they cannot tell me they drive 60kms one way to work and not be on the freeway.
i got my best results with the dealer by taking the service technician on a ride with me and pinpointing each of my problems. The ride was not over until he confirmed that he could see/hear exactly what i saw and heard.
Verify that your trip computer is somewhat (they are rarely perfect) accurate. Pick out a test loop (near the dealer). At the beginning of the test route, reset the computer.i have done this and it is almost accurate. Not far off. They did tell me tho that you cannot go by the gages on the dash for mpg/ltrs as they are never correct. Funny thing with this is they are out by maybe 1 mpg when i do thenumbers for consumption from my receipts. at the end, note the mileage. We already know that you're gonna get less than the claimed 30.1 mpg the dealer claimed.
Repeat the procedure, but this time with the dealers tech driving. If there's no problem, his numbers should be considerably higher than yours. And that's with a similar driving style, driving normally, not trying to artificially raise the mpg. i will need to do this as well
but if he get's bad numbers too, pin him down on it and stay on them until they fix it to your satisfaction.
The other thing though... There's gonna be variation in every engine design. In a perfect world all g6 3.5's would get the same mileage under the same conditions. But in reality power, mpg and driveability can vary by a considerably large margin from engine to engine while being in perfectly good shape. Your particular engine may just be one that is gonna deliver low mpg. It happens.
But 11mpg is outside of any margin that could be considered normal. That's extreme. Did it get good mileage before? Ever? see answer above
did you get this car used? yes. Bought it from the dealer with 20,000k on itbeware that there is a good chance that a used g6, may have been a rental car in it's former life. That in itself opens up a whole can of worms. Rental cars get regular service, but they also have a hard service life. uggh... Scary...
they come off the delivery truck and go straight to the rental lot with, often, less than 2 miles on the odometer. Then they are rented and immediately taken on 500+ mile freeway trips non stop. Or they get thrashed around town. A new engine needs a proper break in, if it is to produce respectable mpg, power, and reliability over it's lifetime. Long trips with steady rpms is not good for a virgin engine. High rpm, high throttle is not good for a virgin engine. But this is exactly the kind of service these fleet units see. Even a regular used car may not have been treated well before you received it. Just something to thing about.
So many factors can effect your mpg. Yes, it's gonna be hard to find out what the problem is. But the dealer should acknowledge the problem and be most helpful in resolving it.
Keep us posted.
i wanted to thank you for all your info... I have some homework to do and that is fine..at least i am not going to twiddle my thumbs not knowing what to do cause the dealer is not being helpful. I will post results when i have them.
I have responded to your posting through out it in bold caps so that you can see the answers.