AWFUL G8 GT MPG so far....

[LongbowFoSho]

Bought the car in late May and MPG was decent at 23 average with a mix of city/hwy. She drove it back from the dealer (~150 miles) and squeezed 27 MPG out of it.

Deployed to Afghanistan in June. The car was getting the persistent whine above 60mph, so she took it to the dealer and they replaced the tranny mount. Fast forward to now and Jess says she is lucky to get 17 MPG, with 13 MPG in the city being the norm. She says she hasn't seen 20 MPG in weeks.

WTF could they have done to that car to kill the mileage? Never mind that the whine is still here, although it manifests at different times now.

Anyone else have any experience with this? The car is bone stock and she doesn't have a lead foot. Even if she left it idling a lot (historically, she doesn't), it still shouldn't be getting less than 17 MPG. Any ideas?

[popsicle]

That doesn't sound right. But with more Ethanol in gas it makes MPG suffer. I have an average of 21 on my computer and I am a little heavy footed

[Zaphod B]

My average MPG always settles around 17 for combined city/freeway driving. The only time I get over 20 is on longer trips that are mostly highway miles.

Not sure what could have made a difference with your car other than maybe having a heavier foot.

[Chewy]

I run Ethanol and see about 21.5 average with 90% highway. Not sure what's up. There are so many variables that can play into this. Make sure something hasn't gotten sucked up into the filter some how. You never know! I've seen birds in them before.

[LongbowFoSho]

The temps in TX have been ridiculously high lately, so maybe that's part of it? A drop of 10MPG seems pretty excessive though, even at 105-110.

[GRRRR8]

Make sure the air pressure in the tires is correct (39 frt 37 rear if stock tires 19s). If she had an oil change done, make sure they put 5W30 in not 10W30.

[wreckwriter]

I get about 1/2 MPG.

[GRRRR8]

^ LMAO! A 1/4 mile at a time. :)

[wreckwriter]

^ LMAO! A 1/4 mile at a time. :)

Mostly 1/8.....

[IcePickFreak]

I've been averaging just over 19mpg with about 60% city, 40% highway driving with mine, only mods are cai, hsrk, tune (AFM turned off), axleback & xpipe. I keep my 19" tires at the recommended 36psi all around per the doorjam sticker. Been really hot & humid here too but haven't seen any noticeable difference than when it's, say, in the 60s. I don't exactly have a light foot either. I'd say with that big of a change there's something bigger at play here, IMO.

[rmcrom]

Don't forget to take off the parking brake.

[Mier]

Make sure the air pressure in the tires is correct (39 frt 37 rear if stock tires 19s). If she had an oil change done, make sure they put 5W30 in not 10W30.

Backwards... 36 lbs in front and 39 lbs in the rear.

[mi04se1]

Im lucky to see 23 on the highway now.

[-Ray-]

My wife is hard on the brakes, so I always get better mileage than her. The saying, "Your mileage may vary", says a lot.

[Mier]

I bet she's running through mexico while you're not around and she sure isn't telling you.

[WickedMom]

I get anywhere from 14MPG on race days up to 28MPG on the freeway.

[LongbowFoSho]

I get anywhere from 14MPG on race days up to 28MPG on the freeway.

That's the thing, though. We were getting excellent mileage until they "replaced" the tranny mount or whatever they did. After that, we're lucky to see 18 ever.

We're still fighting these assholes about the whining at highway speeds. They keep trying to blame the tires (brand new), say its normal (its not), or that there's nothing that can be done about it (there is). I need to find the TSB in a GM manual to show them. I showed them the one from here in the Holden manual, but the dude had the gall to say it was different somehow. I almost went primal on him.

Owning this car so far has been a miserable experience, only because of the hoops you have to go through to get something fixed on the damn thing. It took them three tries to order the right parts for the rear vents. Three!

To top it all off, some jackass swiped the back bumper in a parking lot last week and decided to drive off instead of acting like a human. So now, the paint is starting to peel and its only a matter of time before it has to be repainted.

[Slizzo]

That's the thing, though. We were getting excellent mileage until they "replaced" the tranny mount or whatever they did. After that, we're lucky to see 18 ever.

We're still fighting these assholes about the whining at highway speeds. They keep trying to blame the tires (brand new), say its normal (its not), or that there's nothing that can be done about it (there is). I need to find the TSB in a GM manual to show them. I showed them the one from here in the Holden manual, but the dude had the gall to say it was different somehow. I almost went primal on him.

Owning this car so far has been a miserable experience, only because of the hoops you have to go through to get something fixed on the damn thing. It took them three tries to order the right parts for the rear vents. Three!

To top it all off, some jackass swiped the back bumper in a parking lot last week and decided to drive off instead of acting like a human. So now, the paint is starting to peel and its only a matter of time before it has to be repainted.

TSBs are posted here and on the other boards in their appropriate TSB sub forum. Just glance through them when you get a chance and have them printed out and have the woman bring it to a DIFFERENT dealer. Looks like your current dealer is crap and you need to find one that is more willing to help you out.

Chevrolet dealers should be able to help you out the same as a former Pontiac dealer.