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  1. #1

    Default GM Shop Foreman's response to Bad MPG

    So some of you may know I have been getting pretty bad MPG on my new truck ( 8-10city/12hwy ). I've been getting the run around at GM about the issues when i would take it in to the shop. So this time I took it in today and asked to speak directly to the shop foreman, figured i would get some straight answers that way. The shop foreman was very nice and spent a good 15min talking to me about the MPG of my truck, Below is what i learned.

    First thing he said was that oversized tires are the leading cause of poor MPG ( already knew this ). He then went on to say that in Houston area atlest that Ethanol content at the pumps are not always as stated which can cause the vehicle to get very poor fuel mileage. He said even though the gas is suppose to be 10% ethanol, that he has seen a many of vehicles come in with 40+% ethanol. The foreman said running that high of ethanol will cause my truck to loose a 100miles a tank.

    He said he was going to personally take care of my truck today and he would start with doing a full computer update to make sure all the electronics are up to date as GM has released some better tunes for fuel mileage since my truck was released, next he was going to do an ethanol fuel test to see how much ethanol is in my tank, and lastly we was going to go over the mechanicals to make sure nothing is mechanically causing the issue like brake drag. He would then drive my truck for a bit and calibrate the speedometer with his new GPS device to make sure everything was accurate and hook up a fuel meter to monitor the flow of fuel to calculate actual MPG.

    I have to say i was quite surprised that the Foreman took the issue so seriously, Its a far cry from the run arounds i was getting before about driving habits ect.... The guy also hooked me up with a nice dealer rental while my truck is in the shop. The foreman said the new silverados should be getting 17-21 on the hwy.

    I'll let you guys know how it turns out after i get my truck back.

    Kudos to GM for hiring this guy!

    2009 Silverado 1500
    5.3L / 3.73 G80 / 4spd / 4x4 / LWB/ Ext Cab / HD Tow-Haul
    2.25in ReadyLift Level Kit / 3in blocks/ 3500lb HellWig / 265x65x17 Wrangler AT
    K&N Filter / AirRaid MIT / MagnaFlow 2.25" Dual Exhaust / HyperTech MaxEnergy

  2. #2


    That's great to hear, my best friend is a service manager at a G.M. dealer and he has told me that dealerships have been directed to do everything they can to promote positive customer relations. It's nice to see this, as opposed to all the recent negative posts on G.M. customer service.

  3. #3


    That's good info, for about 2 months I have been getting really bad mpg also, I checked what I could on my truck to see if it was mechanical, but found nothing. I assumed it was the fuel, i am sure Houston isnt the only area with high ethanol, damn gas companies, losing 100 miles per tank that is just ridiculous
    2002 Chevy Silverado & 1995 Ford Bronco

    02 Silverado: 50K miles, 20" Motto Rims, Flowmaster 50 Series
    95 Bronco: 160K miles, 4" Superlift, 33/12.5/15 Mickey Thompson
    01 Civic: 75K miles, DD

  4. #4


    Yeah that guy sounded like he hooked you up ha. Atleast he is gonna make you really happy and resolve the mpg issues.

    2008 Chevy Silverado Ext. Cab Lt Z71 5.3 V8
    7.5 Inch Rough Country Suspension Lift
    RBP Replica Grille Black w Chrome Rivets
    Recon Smoked Cab Roof Lights
    N-Fab Powdercoated Gloss black Cab Length Nerf Steps
    5% Tint over 20% all the way around / 5% Eyebrow Strip
    AVS Smoked Window Visors
    Z71 Stickers Black & Metallic Silver
    Tow Mirrors / Smoked Turn Signals
    XM Satellite Radio Fin / Color Matched
    Interior Plastic Pieces / Color Matched
    Power Acoustic Tweeters
    Painted Bowties / Color Matched
    Painted Door Handles / Color Matched
    Smittybilt Bull Bar / Color Matched
    Custom Rolled Edge Exhaust Tips / Color Matched
    Custom 2.5 Inch Cat Back True Dual Exhaust
    Flowmaster Super 40 Series Dual in / Dual out
    Magnaflow Tru-X Pipe
    K&N Air Filter
    18x9 Rockstars Machined Black
    Center Caps / Color Matched
    33.13.50 Nitto Terra Grapplers
    New Front Wheel Well Liners
    Eagle Eye Black L.E.D. Tailights
    Eagle Eye Black L.E.D. Third Brake Light / Smoked
    Eagle Eye Black L.E.D. Halo Projector Headlights
    Notto HID Kit 10,000k Low beams
    Recon L.E.D. Light Bar
    Buschwacker OE Style Tailgate Cap
    AMI Gloss Black Antenna
    Debadged Chrome Lettering
    Door Molding Removed

  5. #5


    Glad to here you stopped getting the run around. Let us know if he found anything or if the new updates help.

    2005 Chevy Silverado Z71 Crew Cab
    6" Skyjacker lift w/Edlebrock dual front remote resoviour shocks, single rear remote. Rancho skid-plate.
    17" x 9" M/T Classic Lock Wheels, 35" BFG A/T or M/T tires
    4.10 PercisionGears w/factory locker, T/A Performance rear-end cover
    Banks CAI intake, ported throttlebody, JBA coated headers, over-sized Magnaflow cats, Magnaflow cat back exhaust, Diablo tuned
    B&M aluminum deep transmission pan
    Warn brush guard w/Warn 9.5 XP winch, PIAA bulbs, Line-X bedliner, AWS Black tool chest, Extang tonneau cover
    Weather Tech floor mats
    Cover-Craft seat covers
    Dash mat cover
    Formula One window tint
    One black Lab in rear seat.

  6. #6

    Join Date
    Jun 2006
    River Ridge Louisiana-4 miles W of New Orleans-didn't flood-water stopped 800 yards away.


    Sounds like you have a real pro.
    He is right about big/tall tires wheels.
    They travel farther than the odometer knows
    They generally have more rolling resistance-wider-sometimes with more aggressive tread
    They are heavier, so it takes more energy to accelerate them- energy that you waste in the city when you brake it off.

    Also right about ethanol hurting mpg. 10% should drop mpg about 3% but it seems to drop it more like 5-6%.
    I had no idea that sometimes they get the % wrong-I think in Louisiana they can sell 15% gasohol as gasoline- I didn't know that it is sometimes mixed "wrong" and can end up being 40%- never heard that before, but...

    Let us know how it works out.
    My 216,300 mile 1998 Suburban gets and honest 21 mpg on long- 3000 mile- hy trips(62 mph).
    You 5.3 should get at least 1-2 mpg better at 60-62 mph- and about 20 mpg at 65-70.
    1998 suburban-
    1/2 ton

    199500 miles

  7. #7


    I am glad to hear about the positive experience. Please feel free to keep us posted.

    Tricia, GM Customer Service.

  8. #8


    Just heard back from the shop foreman. He said he checked the mechanical stuff out on the truck first and found nothing wrong, then tested the fuel quality. The fuel was excellent with 9.5% ethanol. He then filled the truck up and drove 60miles down the hwy and calculated the MPG at 8.2 mpg. He then updated the computer to the latest tune and repeated the same process and got 16.7 MPG @ 70mph.
    Hes also replacing the Slip-Yoke which has a TSB on it, and the truck will be ready in an hour.

    Damn good work GM!

  9. #9


    Good to hear you were able to get some satisfaction. Once again it proves my opinion that the first fact of life is that you never start an coversation by saying " Hey Look ***hole!"

  10. #10


    Hey man i got kinda bad gas mileage too before my lift all i had was 33's and a leveling kit though. The update could i put one on my 2008 silverado would this work or no?

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