2010 LS3 Gas Mileage Problem
Thread Starter
3rd Gear
Joined: May 2007
Posts: 3
Likes: 0
2010 LS3 Gas Mileage Problem
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?
Tech Contributor
Joined: May 2008
Posts: 2,843
Likes: 16
From: Howell Michigan
St. Jude Donor '09-'10-'11
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. 
SUBVETTE
Joined: Jul 2006
Posts: 3,841
Likes: 90
From: San Diego CA
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.
Pro
Joined: Sep 2009
Posts: 536
Likes: 2
From: Los Angeles California
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.
Team Owner
Joined: Jun 2005
Posts: 46,295
Likes: 2,596
From: Northern, VA
St. Jude Donor '15
"In honor of jpee"
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. Corvette Stories
The Best of Corvette for Corvette Enthusiasts
10 Most Common Corvette Problems of the Last 20 Years!
Joe Kucinski
5 MOST and 5 LEAST Popular Corvette Model Years in History!
Joe Kucinski
2027 Corvette Buyer's Guide: Everything You Need to Know!
Joe Kucinski
10 Things C8 Corvette Owners Hate (But Won't Tell You)
Joe Kucinski
10 Best Corvettes Coming to Barrett-Jackson Palm Beach 2026!
Brett Foote
Every Corvette Grand Sport Explained! (C2, C4, C6, C7, & C8)
Joe Kucinski
Grand Sport & Grand Sport X Launch Alongside All-New 535hp LS6 V8!
Michael S. Palmer
5 Reasons Bad Drivers Crash & 5 Ways to Avoid a Costly Mistake!
Joe Kucinski
7 Bolt-On Upgrades From Extreme Online Store to Level Up Your C6 Corvette
Pouria Savadkouei
Thread Starter
3rd Gear
Joined: May 2007
Posts: 3
Likes: 0
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.
Melting Slicks
Joined: Oct 2007
Posts: 2,702
Likes: 192
From: Northwestern Connecticut
St. Jude Donor '10 thru '26
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.
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.
Instructor
Joined: Apr 2008
Posts: 224
Likes: 0
From: Garland TX
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?
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
Burning Brakes
Joined: Dec 2007
Posts: 1,015
Likes: 1
From: Maryland
St. Jude Donor '08
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?
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?
Heel & Toe
Joined: Jan 2009
Posts: 20
Likes: 1
From: Kernersville NC
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.
Racer
Joined: Mar 2002
Posts: 287
Likes: 5
From: Northampton MA
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.
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.
Le Mans Master
Joined: Aug 2009
Posts: 5,437
Likes: 4
From: Bucks Co. / outside Philadelphia PA
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.
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.
Observe how your car comes to a stop with the clutch in.
Melting Slicks
Joined: Feb 2006
Posts: 2,172
Likes: 103
From: Des Moines Iowa
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.
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.