2020 GMC AT4 MPG Disapointed

Elpresidente · November 4, 2019

Bought a 6.2L wanted a 3.0 Diesel but the UAV strike robbed me of that; having to buy a vechicle in the 2020 tax year.

Have to say on mixed driving 75mpg highway and some city getting 15.3mpg combined by the computer. Disappointed to say the least. In California running 91 octane vs 93 as do not have access to 93.

3.23 rear end. Tires are to be inflated to 35psi have them at 40psi.

Reset the second trip odometer at 1000 miles. Got basically the same number.

Auto start stop feature is on; as well this does have the new skip fire v8.

Have the stock 20” tires; the duller the less aggressive tread than the duratracs which should help with mpg.

was suppose to get 15city / 19 highway for 17 combined. Really it’s closer to the city number in real world.

Edited November 4, 2019 by Elpresidente

SamDSJR · November 4, 2019

This is normal behavior to me. In my experience it never gets what they say. I just got a brand new 2019 too. So far for me its getting better than my 2018.

On my 2018 I only got 17 mixed true mpg. The computer would say 19, but it was always off by 2. Best I ever saw (with my driving habits) was highway trip only and I could get the computer to go to 24, which really was 22.

Now, I did one time do a highway trip at 55mph, and the computer said 27!! But I lost my mind after like 15 minutes and started driving normal 65-80mph highway speeds. LOL.

TJay74 · November 4, 2019

1st until the truck has at least 10k miles on it and the engine is fully broke in the real world gas mileage will be off. 2nd if you are going off of the DIC it will not be close at all, they are always off at least 1mpg at the minimum as that info is based off of the injector flow data.

The best way to find out the gas mileage is to fill the tank up, reset the trip mileage and drive until you fill up again. Then divide the miles driven by the gallons it took to fill up and that will be your actual gas mileage. Bear in mind that winter gas gets less gas mileage than summer gas and remote start events kill gas mileage along with short drives during the colder months.

econometrics · November 4, 2019

4 hours ago, Elpresidente said:

Bought a 6.2L wanted a 3.0 Diesel but the UAV strike robbed me of that having to buy a vechicle in the 2020 tax year.

Have to say on mixed driving 75mpg highway and some city getting 15.3mpg combined by the computer. Disappointed to say the least. In California running 91 octane vs 93 as do not have access to 93.

3.23 rear end. Tires are to be inflated to 35psi have them at 40psi.

Reset the second trip odometer at 1000 miles. Got basically the same number.

Auto start stop feature is on; as well this does have the new skip fire v8.

Have the stock 20” tires; the duller the less aggressive tread than the duratracs which should help with mpg.

was suppose to get 15city / 19 highway for 17 combined. Really it’s closer to the city number in real world.

How much idling are you dong? You're in CA, so you're probably still using the AC, and doing a lot of waiting in drive-thurs, traffic, etc?

My 5.3L MPG was not very good this summer. Doing remote starts, I noticed that I would lose 1mpg per 4-5 min of truck idle. Same with sitting in the drive thru, etc.

These kinds of things really skew your DIC MPG numbers.

Now that it's cooled off here in DFW, I'm getting closer to 17-18mpg per tank again, which is what I was getting back in the spring with my mostly city driving.

Elpresidente · November 4, 2019

Live in very south OC. Live where the traffic on the I5 is light. Twenty some miles south of Huntington. So do not get stuck in traffic a great deal. Nothing more than normal traffic light stops the same across any suburban part of the nation. On balance with the highways open i usually am 75 to 80mph where it allows.

The AC is on all the time. Which does have a draw; plus it reduces the amount of time the stop is active for the start/stop system.

Find that about half maybe a third of the time; at lights the start stop system does not Stay off for the entire duration of the light. Think the AC is turning it back on.

Edited November 4, 2019 by Elpresidente

i82much · November 4, 2019

I'm not surprised. I got 13.5 mpg doing 80 mph on a long interstate trip in my 6.0 2500HD truck. I thought about getting a 1/2 ton to get better gas mileage but after talking to a few people it sounds like at those speeds the mileage isn't much better, my brother figured he would have gotten 15 or so on the same trip in his 5.3 Tahoe.

The cylinder deactivation might make a big difference if you slowed down to 60 mph.

Elpresidente · November 4, 2019

Went back an re-read the replies. Not sure what remote starts mean?

Remotely starting the car from the key fob, or the start system, or stop and go traffic?

Ha okay as well. Will fill up and start tracking mileage. If you are all saying am getting 15 mph on the cluster is high and am really getting lower. Will reply back when i know more.

As well never understood why people say engines get better mileage after X distance on the odometer. Never made sense to me, the rings are wore in after a1000 miles. Its all the same air fuel ratio and injector tables in the computer..

wizard4878 · November 5, 2019

I know its a little like comparing apples to oranges but my 5.3 has done nothing but impress me. Was late to an event saturday night and had the cruise set at 85 on the interstate for about 40 miles, (80 round trip, ran about 75 on the way back) some flat, some hills and was expecting about 14mpg. I topped off the tank when I got back and showed an average of 20.2 on the dash, 19.9 with the calculator

SeTex · November 5, 2019

21 hours ago, Elpresidente said:

Bought a 6.2L wanted a 3.0 Diesel but the UAV strike robbed me of that; having to buy a vechicle in the 2020 tax year.

Have to say on mixed driving 75mpg highway and some city getting 15.3mpg combined by the computer. Disappointed to say the least. In California running 91 octane vs 93 as do not have access to 93.

3.23 rear end. Tires are to be inflated to 35psi have them at 40psi.

Reset the second trip odometer at 1000 miles. Got basically the same number.

Auto start stop feature is on; as well this does have the new skip fire v8.

Have the stock 20” tires; the duller the less aggressive tread than the duratracs which should help with mpg.

was suppose to get 15city / 19 highway for 17 combined. Really it’s closer to the city number in real world.

I have about 4k miles on my 6.2. I avg 17 mpg most of the time with a mix of city and highway. Highway 18-20mpg depending on speed and wind. If I'm in town all the time 13-14mpg is about what I get.

eppieguy · November 5, 2019

I'm averaging 15.7 on my daily commute with is a combination of a lot of stop and go and a little highway, 20 miles each way. I have a 3" lift and 34.5" E rated 22's. I've gotten as high as 18.5 MPG as my best. I have also corrected the speedometer via the Hypertech so my assumption is the MPG's would be correct as well.

truck_newbie · November 5, 2019

On 11/4/2019 at 9:03 AM, Elpresidente said:

Bought a 6.2L wanted a 3.0 Diesel but the UAV strike robbed me of that; having to buy a vechicle in the 2020 tax year.

Have to say on mixed driving 75mpg highway and some city getting 15.3mpg combined by the computer. Disappointed to say the least. In California running 91 octane vs 93 as do not have access to 93.

3.23 rear end. Tires are to be inflated to 35psi have them at 40psi.

Reset the second trip odometer at 1000 miles. Got basically the same number.

Auto start stop feature is on; as well this does have the new skip fire v8.

Have the stock 20” tires; the duller the less aggressive tread than the duratracs which should help with mpg.

was suppose to get 15city / 19 highway for 17 combined. Really it’s closer to the city number in real world.

The mpg will improve with mileage. When i first purchased my truck, i couldn't get better than 15mpg which sounds like what you are currently experiencing. I'm a shade under 4k right now and i consistently get 17 mpg in mixed city/highway. On my last road trip which included a highway stretch of over 250 miles at 70mph+ with a ton of slow-downs, i averaged 23mpg. Pic below. One thing to keep in mind is trucks are not very aerodynamic and the drag takes a bad turn when you go over 70 mph. One thing you can do to help is install a hard tonneau cover if you don't already have one. AC on/off makes no difference when on the highway. I'm actually seeing lower mpg in the cold weather without AC than i did in the summer with AC.

RaisedByWolves · November 6, 2019

On 11/4/2019 at 6:48 PM, Elpresidente said:

Went back an re-read the replies. Not sure what remote starts mean?

Remotely starting the car from the key fob, or the start system, or stop and go traffic?

Ha okay as well. Will fill up and start tracking mileage. If you are all saying am getting 15 mph on the cluster is high and am really getting lower. Will reply back when i know more.

As well never understood why people say engines get better mileage after X distance on the odometer. Never made sense to me, the rings are wore in after a1000 miles. Its all the same air fuel ratio and injector tables in the computer..

There’s a lot more involved than just the rings seating.

Every sliding and or rotating part needs time to get loosened up.

KozzyJr · November 16, 2019

Winter here my mileage is shit. But I have a 6.2 with heavy E rated duratracs. My over all average is 19.5 litre per 100km. Buts it’s been -20 here

J2Jones · November 16, 2019

I have a 6.2 and am averaging about 18 MPG on commute of mostly highway driving at 70MPH or so. Both by in dash computer and manual calculations. I’m at about 4,400 miles and have averaged 17.9MPG based on trip computer that hasn’t been reset since purchase. I’m happy with it. About the same as the Toyota Highlander I was driving previously. I do mainly use 2WD mode which seems to be a little higher than when I run it in 4-wheel auto.

Hydro4acid · November 16, 2019

On 11/4/2019 at 4:47 PM, i82much said:

I'm not surprised. I got 13.5 mpg doing 80 mph on a long interstate trip in my 6.0 2500HD truck. I thought about getting a 1/2 ton to get better gas mileage but after talking to a few people it sounds like at those speeds the mileage isn't much better, my brother figured he would have gotten 15 or so on the same trip in his 5.3 Tahoe.

The cylinder deactivation might make a big difference if you slowed down to 60 mph.

In my 2020 6.2 Denali, going 75-80 I got 23-25 mpg over 500 miles. I'm pretty pleased with this truck on the highway. Power when u want, mileage when u need it.

Edited November 16, 2019 by Hydro4acid