jfdicurt

I recently traded my 2007 C6 automatic for the new 2010 Grand Sport with manual trans. My 2007 LS2 routinely got 30 MPG at freeway speeds of 70-75 mph. For some reason, the new car can barely get 21.5 MPG at those same speeds. All of the other LS3 owners in the club are getting high 20s on the same roads. I have checked the tune with HP tuners (completely stock) against other stock tunes to make sure nothing is different. Everything looks good. Any ideas?

DannyBoyC6

Unfortunately, I think you need to take it in and have your dealer look it over. My opinion.
Good luck!

articvett

How many miles ?MPG wil go up as it breaks in.

Eric D

How many miles? Your shifting habits can change mpg too. Maybe switch with one of your club members and see if they get better mpg. At least you would know then if it is you or the car. Also, are you comparing your GS to a standard LS3 Corvette? Big difference in many things, like tires, gearing, weight, and more.

SUB VETTE

It should imrove with some miles put on it, especially if you haven't finished the break-in period yet. Thev first tank of gas that my LS2 saw gave me 16.5 mpg on the highway but after several hundred more miles, and break-in period done, I was getting 28mpg highway at 80 mph.

bps999

could vary with the road, slight hill, wind, etc. I would give it some time to be sure it's not getting normal mileage. Some people tend to exaggerate their mileage a bit too... quoting numbers from very short tests, or especially favorable conditions.

pmj341

We just picked up a 2010 C6 A6 Saturday and my wife got 28mpg on the way home, I was upset I only got 25 mpg on mine.

AORoads

excellent idea if you go cruising with them in a bunch.

bps999

ya then leave their car in 3rd gear the whole time and tell em, wow yours is only getting 11mpg. you'll feel loads better. just kidding...

jfdicurt

Thanks all.... The 21.5 MPG was on a long highway trip - a trip from Vegas to Ely for the Silver State Classic. It was about 250 miles on pretty flat open highway - very little shifting involved. Speed limit the whole way (a ticket gets you disqualified from the event so everyone drives the speed limit on the way up there). I had also done a shorter trip recently and got about the same results. I spoke to the dealership mechanic - they will "call it in" to the factory but I don't get the feeling they are going to find anything. I was thinking about doing some coast down tests next to another LS3 car (coast from 80MPH to zero to check for excess drag or something binding up more than normal). Not sure what else to do here. It is significant enough to really bug me - I am going to the gas station twice as often as I was in my 2007 - it is my only car so it affects my monthly budgets, etc. I obviously didn't buy the car for just gas mileage - but I think it should at least get mid twenties on the road.

68sixspeed

The only time I saw something like this was on a pickup, turned out the mass airflow sensor was dirty. Might be worth cleaning or swapping between cars, maybe it's just a bad sensor making it run rich? (could be any of a number of sensors though, knock sensor, o2, intake air temp, etc.) A ride-along with a snap on or other tool plugged in by the dealer may show something off.

How is the car under power? Any chance of a cam being phased wrong? Heck, I get 28mpg out of my z06, I wouldn't think you'd get less.

Cherokeedoc

Have you checked your wheel alignment ????? and how about tire wear ?? Vette alignment specs are plus - minus a mile . I ruined my tires in 4,000 miles, before finding a good Hunter man that set every thing to nominal !!!!! Tires dragging side ways will affect gas mileage and disposable income.

Gas additives mandated nationwide reduced mine from 30 to 27, problem is 10% is the min some fuel has 20% Ethenol and more is being considered by the Washington azzhats.
Best I can do at 74 mph a/c on was 27.5 on a 2000 mile trip.
Check your alignment, tire pressures.
Happy Cruising
Harry

wooden

something is wrong, I get 23 mpg on that same stretch of highway with a 416 super charged with 3.90 gears, running 345,s in the rear.

AORoads

Question: are you sure you are in 6th gear during these cruises and trips? what's your rpm at 60 mph?

C6LSx

I have a 2008 LS3 A6 NPP with approx 2000 miles.

I have been averaging approx 20 and 21 mpg regarding intown and limited highway driving.

Speeds avg has been between 40 and 60mph.

Does my mpg sound about right for now and should it improve with extended highway driving at speeds between 60 and 70mph?

MEN6107

I'm seeing the same thing. I got 30.6 mpg on a 200 mile highway trip the week before I traded my '07 coupe with MN6 and Z51 on a '10 GS coupe with MN6. With 1400 miles, it's averaging 22.5 on the same trip. Dealer says nothing is wrong but I'm not buying it. After I drive for 30-45 minutes, it seems like the drivetrain is binding or the brakes are dragging. At 70 mph in 6th gear, it's turning about 1750 rpm.

smonska

Sadly, I think you're getting about what a GS gets. I have a 2010 GS manual couple with 2300 miles on it now, and my average is about 20mpg. That includes about 1400 of those miles being highway.

A GS has huge disc brakes (more drag), huge tires (more drag), wider body (more drag) and, most importantly a 14% LOWER .57 6th gear, that's 14% more RPMs on the highway than a regular LS3 'Vette (.50 6th). Z06s don't have this lower gearing so they aren't a 1:1 comparison so to speak.

EDinPA

Also a 2010 gs coupe with a manual. It took about 3500 miles before it broke in enough to roll freely on a slight slope. Break in is more than 500 miles.

Observe how your car comes to a stop with the clutch in.

jimmie jam

wow, you are not happy with the MPG? my 5,200 mile 07 A6 GQ gets between 13.4 and 17.8 mpg. maybe my DIC "2" digit is burned out

jovette

My average mpg on my GS is in the low 20s as well. I now have over 3,100 miles on my GS/MN6 and I can't seem to come close to the 26 mpg for highway driving posted on the window sticker.