2014 GMC Sierra 1500 mpg

Juan_ID · August 2, 2016

Hey there guys new GMC Sierra owner, bought a 2014 crew cab standard box base model Sierra last week and had a couple questions in regards to mpg. I love the truck and the extra room having come from a 2012 GMC Canyon crew cab but the mpg is not too good. The truck has a 2.5" leveling kit some aftermarket 18" wheels and 275/70r18 BFG KO2's other than that all stock. I am planning to do a blackbear tune here soon but would like to figure out the mpg thing first. I have put close to 1000 miles on the truck since buying it and the best I have gotten is 12.8mpg. That's a big range of driving from 80 on the freeway (Idaho speed limit) for at least 300 miles, maybe 200 miles in town or around the hills and short commutes between 10-15 mph and 20-45mph and some 60-65mph driving for another couple hundred miles. The truck has the 5.3 and 6 speed tranny with the 3.42s I believe. I don't remember for sure but my canyon averaged anywhere from 13-18mpg, had the 5.3 with 4.10 rear end. I will admit I don't baby it a lot but was expecting a little more maybe around 15-16mpg average or better? Am I way off in being concerned about it and this is normal or could there be an issue? I have read people on here with the same and or bigger lifts and tires getting 18-21 average. Thanks for any info you guys can give

Rawyzf · August 2, 2016

Seems a tad low, but you do have a level and 33" tires (email rated I assume).

Validate you're not stuck in 4wd/awd. There was a recall for the transfer case, make sure it was performed.

Sent from my SM-G930V using Tapatalk

Kyle919 · August 2, 2016

The speedo could be off which would make the mpg on the computer wrong. Have you calculated the mpg yourself?

toro1966 · August 2, 2016

Wow - I get 22 on the highway with my 6.2. That sounds like dodge mileage

truckguy82 · August 2, 2016

I have the 6 speed, 3.42, but the 6.2L, which should be similar in mpg.

Completely stock though

My real world MPG in suburbia (25-40mph roads with stop signs) is 11-12mpg

Real world mpg on the highway setting cruise @ 75mph is like 21mpg

Best thing would be to do is set your cruise on a certain speed for 25 mile and get the average.

These trucks sip fuel while maintaining speed, but drink it while accelerating

Juan_ID · August 2, 2016

Seems a tad low, but you do have a level and 33" tires (email rated I assume).

Validate you're not stuck in 4wd/awd. There was a recall for the transfer case, make sure it was performed.

Sent from my SM-G930V using Tapatalk

Yes tires are E rated, I will check on the transfer case even though I know it's in 2 wheel drive.

The speedo could be off which would make the mpg on the computer wrong. Have you calculated the mpg yourself?

Yes I hand calculate my mpg, I have never used the computer.

TxTruckMan · August 2, 2016

The lift and heavy tires are hurting you, but your tires are also taller than stock. So you're speedo is likely off by 5% unless it was adjusted (unlikely). Also, 80 mph will kill your MPG. IMO, 75 is about the point where it starts to drop off significantly. And with your speedo being off, your 80 mph, was closer to 84 mph, so definitely pushing a brick through the wind. Do you have the lower valence or was it removed?

TxTruckMan · August 2, 2016

Oh, if hand calculating, add 5% to your mileage traveled.

Juan_ID · August 2, 2016

The lift and heavy tires are hurting you, but your tires are also taller than stock. So you're speedo is likely off by 5% unless it was adjusted (unlikely). Also, 80 mph will kill your MPG. IMO, 75 is about the point where it starts to drop off significantly. And with your speedo being off, your 80 mph, was closer to 84 mph, so definitely pushing a brick through the wind. Do you have the lower valence or was it removed?

Yes I doubt it's been adjusted, going to call the dealer and see if that's something they can do if not then the blackbear will be on it's way soon. And yes the valence has been removed but if that makes a significant difference I will throw that baby back on!

Juan_ID · August 2, 2016

Also the computer showed 13.6mpg for the last tank of gas I ran, and I calculated 12.8mpg and if I remember right it was about 323 miles traveled if that helps any.

Aldila · August 2, 2016

Good point about speedo if it hasn't been adjusted. I had a 2014 5.3/6 speed with 2.5" level and 1.5" body lift. I also had 20x10 wheels with 295/55/20 tires and could get 15.2 at 75 mph. I'd say something is off with your case, as my wheels/tires weighed 103 pounds each.

Rawyzf · August 2, 2016

Also the computer showed 13.6mpg for the last tank of gas I ran, and I calculated 12.8mpg and if I remember right it was about 323 miles traveled if that helps any.

I just did backwards math on this to give you a better actual MPG based on your tire size.

323 / 12.8mpg = 25.23 gallons.

Take your 323 x 1.048 (tire size difference (4.8% larger than oem)) = 338.50 Miles

338.5 / 25.23 gallons = 13.41mpgs.

Juan_ID · August 2, 2016

I just did backwards math on this to give you a better actual MPG based on your tire size.

323 / 12.8mpg = 25.23 gallons.

Take your 323 x 1.048 (tire size difference (4.8% larger than oem)) = 338.50 Miles

338.5 / 25.23 gallons = 13.41mpgs.

Thank you for that, still pretty crappy tho. Is this mpg to be expected?? Would it make a difference if I put a little more rake back into the stance? As it sits now it's got about 1/2", I wouldn't mind 1-1.5" if it will help more.

Rawyzf · August 2, 2016

Thank you for that, still pretty crappy tho. Is this mpg to be expected?? Would it make a difference if I put a little more rake back into the stance? As it sits now it's got about 1/2", I wouldn't mind 1-1.5" if it will help more.

I think that is a bit low for a truck that isn't lifted. If you had a 3-5" lift, I might expect that....but being just leveled with 33" tires really shouldn't be that big of a hit. However, there are a crap ton of factors that play into MPGs. Wind, AC, MPH, Hills, coasting, grade of gas (87/89/91/93) etc. It's all over the board.

Are your tires E rated, and if so, what PSI do you have them at?

I get 13ish on e85. I get about 18ish on 91oct.

Juan_ID · August 2, 2016

I think that is a bit low for a truck that isn't lifted. If you had a 3-5" lift, I might expect that....but being just leveled with 33" tires really shouldn't be that big of a hit. However, there are a crap ton of factors that play into MPGs. Wind, AC, MPH, Hills, coasting, grade of gas (87/89/91/93) etc. It's all over the board.

Are your tires E rated, and if so, what PSI do you have them at?

I get 13ish on e85. I get about 18ish on 91oct.

Yes tires are E rated and they're sitting about 42psi per the tire shop. I have been running 85 octane I believe. Same thing I ran in my Canyon