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2012 ext cab gets terrible fuel mileage from new- 12mpg

Joneebgood2

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Joneebgood2 New Member

Joneebgood2

Posted
Posted

I purchased a new 2012 GMC SLE ext. cab short box 4x4 , 5.3l, 6spd. 3.42 axle,V4/V8 cylinder deactivation in March. I almost have 2000 miles on it now. The fuel mileage has been extremly poor and is a huge disapointment.

 

Sticker says "15 mpg City (12-18) and 21mpg Hway (17-25)"

 

To and from work is about 5 miles country roads, 5 miles highway, and 5 miles within the city. The first three tanks I babied the truck to "break it in". Mileage was 12.9, 13.0 and 12.6. After the first 500 miles I may be driving it more "like I own it" but I am 62 years old so I don't have the heavy foot I used to have - latest mileage was 12.5

 

I have made two trips on the interstate of about 300 miles each (200 at 73mph and the rest on country roads) Both trips got mileage of 15.6- That is the best I have ever gotten??

 

I haven't called the dealer as I know mileage is mainly affected by the driver's habits but this is not the first ext cab GM I have owned. I traded in my 99 Silverado with the exact same body and exact same drivetrain and rear ratio(except old auto was 4 spd not 6). With 255,000 miles and not tuned up in at least 50k I was getting 13-14 around town (12 in winter) and often got close to 20 on the same trip above that I can't even get 16 mpg on now?

 

My mileage doesn't even reach the LOW estimate for Hway driving! How can a vehicle that is 13 years newer technology and even has the Cylinder Deactivation feature get LESS mileage than my old worn out truck?

 

Yes, I love my truck and would still have purchased it even if the sticker had indicated poor mileage but WTF?

 

Probably the dealer can "detune" the computer program to increase my mileage but....... this truck sure runs awesome just the way it is!

 

I did have a K&N intake filter on the old truck- could that make such a difference? I may try that again but I am still really concerned that I cannot get better than 15.6mpg when the sticker boasts 17-25mpg!I

 

Anyone else have this experience / complaint??

 

What to do?

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j-ten-ner Senior Enthusiast

j-ten-ner

Posted
Posted

E-brake?....just kidding...

 

My truck is a 2007, 5.3L with fuel management, crew cab, short bed, 4 speed auto.

Almost the same as yours. I get in the city 14-15 mpg and on the highway 19-23mpg.

 

The mileage should increase after the drive train is broken in. I would go to the dealer and get it fixed.

 

so long

j-ten-ner

tazerbro Enthusiast

tazerbro

Posted
Posted

I have nearly the same config but 2011 with CC.

 

I do very similar driving as you and average around 15.3mpg according to the DIC. I know the reason is in how I drive it. I've also accepted the fact that I don't think I'll ever see any overall average like 20mpg. or 19mpg. or 18mpg. Its my experience and complaint..course I didn't buy it to be good on gas either. I'd be happy with 17mpg and I'm sure sometimes I may average that. I think its the times where I'm doing some spirited driving that brings that average down overall. Which brings me to my meager 15.3mpg average. Thats my thinking anyway..as far as how to make it better? Drive slower :lol:

Lv1G6He3V2 Enthusiast

Lv1G6He3V2

Posted
Posted

Something doesn't add up: same driver, better tech, and worse mileage.

 

Did you switch fuels? There seems to be a difference in mileage with ethanol vs. traditional gas.

TimmyG Senior Enthusiast

TimmyG

Posted
Posted

My 11 cc 5.3 avg 18mpg,60% freeway/40% city

 

Sent from my ADR6400L using Tapatalk 2

Silverado4x4 Senior Enthusiast

Silverado4x4

Posted
Posted

You dont say what part of the country you live in, is it in the north? You still might be on winter blend fuel. They dont start seeing better mpg till after 5000 miles or so because the drivetrain is broke in around that time. No the K&N filter doesnt make any differance in mpg's. Type of fuel will make a big differance also.

 

When I had my 08 5.3 it was happy around 65 on the highway which I got 23 mpg and any faster the mpg dropped off alot. Around town it got about 14-15 mpg.

 

Bottom line, give the truck more time and mileage.

MikeNH Senior Enthusiast

MikeNH

Posted
Posted

Don't trust the sticker, you'll never average over 20 MPG unless you drive exclusively on table flat interstate at 50 MPH with a tailwind. The best I can coax out of my truck with the same configuration is about 18 (hand calculated, not the trip computer). Normally I see between 15.5-16.5 overall average. What mode do you keep the transmission in? I never, ever keep it in drive. I use M4 around town (up to 35-40 or so) M5 on the outer roads (45-50 or so) and M6 at higher speeds. Sometimes I think the trans tires to get to too high a gear for the speed and it lugs the engine and you end up downshifting all the time anyhow.

Daryl LBZ Senior Enthusiast

Daryl LBZ

Posted
Posted

I wouldn't get to worried about it until you hit atleast 5000 miles that seems to be around the time when there broke in pretty good. I had an 09 5.3 4spd Trans that Averaged 16.3 MPG and my area is pretty hilly. Now my new truck (6.2, 6spd trans, 3.73 gears) is getting 14.4 as of now with around 6,500 miles on it. I don't think thats to bad, and I'll be happy with that if it's the best MPG I get out of it.

JrocK817 Enthusiast

JrocK817

Posted
Posted

Something doesn't add up: same driver, better tech, and worse mileage.

 

Did you switch fuels? There seems to be a difference in mileage with ethanol vs. traditional gas.

 

 

:withstupid: I average 13.2 with my 03 AWD Silvy SS. Id say 50/50 hwy city miles. Unless you are running ethanol all the time you should be getting better mileage than that.

ram1067 Enthusiast

ram1067

Posted
Posted

15-16.5 on my 06 w/65k.......just the nature of the beast. i noticed a little in provement when i changed to 0w-30 mobil-1 syn.

MikeNH Senior Enthusiast

MikeNH

Posted
Posted

I have a 2012 crew cab and I average 16-17 city and 20-25 highway. I only have 1100 miles on the truck.

 

Sent from my DROIDX

 

 

 

What engine and axle gears? Are you using US gallons? Is this from the DIC or hand calculated. 20-25 MPG on the highway is not happening unless you're doing that stupid hypermiling crap and even then maybe. Sorry but I'm calling BS.

cs300823 Enthusiast

cs300823

Posted
Posted

I have an 07 CC Silvy 6.0 V-Max... and honestly until I got around 5000 miles did it seem to get good mileage...but even at that I was only getting around 16-17 around town and 20-23 on the highway...Since switching to E-Rated tires since I haul a good size trailer around at times has it dropped to around 14-16 and 18-21 so don't give up on her :0)

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