Welcome to the forum.

I did not buy my truck until 30K miles, so I do not know about break in. Sounds like a real problem, your real MPG is super low, even your DIC MPG is low. Unless you are towing some kind of gigantic trailer? Did you check your speedodometer with your phone yet?

I am battling MPG problems, but nothing like that. My DIC says 17.5 mpg, but my real mpg depends on the number of regens between fillups 1 regen = 16.5 mpg, 2 regens = 15.5 mpg, 3 regens = 14.5 mpg.

I tow a ~4500 pound boat with a T-Top and it does not drop the mpg but 1 or so.

They just replaced my in-tank fuel pump (brass bits in the filter) and I am hoping that solves the problem. I have yet to refill to get real mpg, so I can't say yet.

Good luck-

 

Yeah, these are big heavy trucks. I only get 16mpg with a 2500. Drive easy and on rural roads with not much stop and go. On a long trip at 60mph I got 19mpg once. Not bad for a truck with 450hp and weighs 8000lb. Some of these claims of 23mpg or better are far fetched.

Driving habits will have the biggest impact on mileage.

 

Yeah, these are big heavy trucks. I only get 16mpg with a 2500. Drive easy and on rural roads with not much stop and go. On a long trip at 60mph I got 19mpg once. Not bad for a truck with 450hp and weighs 8000lb. Some of these claims of 23mpg or better are far fetched.

Driving habits will have the biggest impact on mileage.

Lots of truth here.

There is a break-in period, and mileage should go up after a few thousand miles are on the truck. I wouldn't expect much better than 16mpg combined, though. Highway you should see just under 20 mpg if you're nice to it and don't go over 65-70mph unloaded.

 

I’ve owned several Duramax trucks that were bought brand new. There is no increase after this mythical “break-in” period. It’s a truck made to tow and haul very heavy loads. I’m not sure why you are concerned with what the mileage is when driving empty, what’s your mileage while towing? Either way, it’s not rated for a certain mileage, what you get is what you get and there is nothing a dealer will do to help you if you raise the concern with them. If you are concerned about mileage you bought the wrong vehicle.

 

Around town mpg is atrocious on these trucks IMO. Highway is decent until you get over 70mph. Mine is lifted with 37s so it is way worse than stock..........

 

Fuel mileage is one of the reasons I sold my 21. One long trip I got 13 mpg the next I got 11 mpg. I had my mind made up on the way home that it had to go. Especially coming from a lml that was great on fuel.


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So I'm new to this forum but not new to Duramax's. I now own a 2021 GMC 2500HD AT4 with about 5K miles on it so far and to me is getting terrible mileage. Since new, I'm averaging 12 MPG. I've owned it since May 1st, I've towed my boat (24' CC) twice for two days, my car hauler (24' enclosed) four times and during towing I'm getting 8-10 MPG but around tow or highway, I can barely get better than 14-15 MPG. All stock, no edits to the truck since new. My GMC "smart app" say I'm driving like a cautious granny. My score if consistently in high 80's to low 90's. I've taken it to my GMC dealership and they "say" all looks good and it is performing fine. I have at least 4 friends with the same truck (Chevy and GMC) and they are getting 20+ and some in the mid to high 20's MPG's with lower driving scores. WTH heck is wrong with mine?

Reading the above post, maybe these GMC's aren't getting very good mileage after all... 🤦🏻‍♂️

Thanks in advance, Ben

 

I have at least 4 friends with the same truck (Chevy and GMC) and they are getting 20+ and some in the mid to high 20's MPG's with lower driving scores. WTH heck is wrong with mine?

Your friends that are claiming mid to high 20's are full of BS, and you should put your boots on before talking to them. Anyone who claims they can average, AVERAGE, above 22mpg is smoking the good stuff. It's not realistic. Can you get 25mpg on a random stretch of highway going 65mph with no wind and flat elevation? Sure can. But that is the exception and not the rule.

An HD truck is going to average around 15-17mpg empty cruising around, mixed driving. Put bigger tires and a lift on and you're 13-15, no exceptions.

Towing you're going to see 12mpg average if you're towing responsibly. If you're giving her the juice because it's Friday afternoon and the fish are biting up north, then you're going to see 10 or less.

These are facts. Salesmen lie. Fanboys lie. Dodge owners lie.

(I threw that last one in there to stir the pot.....but, for real.... Dodge owners.... )

Please remember I'm talking average mpg here. Not what you can finesse out of it under optimal conditions. These trucks are not aerodynamically efficient, nor are the things we hook behind them.

 

I noticed a substantial jump in mileage between 6500 and 7000 miles. Highway improved at least 1 if not 1.5 MPGs and has held that for the last 4k on the truck. I have hand calculated since I drove it off the lot. Overall best highway tank on a 65 mph roads is 21.2. Current average without trailer is 17.5, with our 7k travel trailer about 12.

My old HD was the 6.0, so these numbers are great for me. That truck with the camper was between 6 and 8 mpg on the interstate.

 

Going downhill coasting I get 99mpg. But I average 14 back and forth to work.

 

going to and from work I get around 18-19mpg highway on flat stretches I've seen as high as 24 for straight short stretches but it drops going uphill. my 500 mile average is around 17.8mpg. I primarily drive cruise control at anything over 25mph. I've noticed much better mileage using cruise control.

 

Imo

if anyone is getting 18-21 out of a 3/4 ton truck they are doing well and have great driving habits.

anything over 21 I call bullshit on.

 

I just finished a 525 mile trip from Colorado to Utah pulling a 40 ft 5th wheel ('21 one ton), which finished with a 30 mile, 1K ft, downhill run. Before the downhill run I was getting about 10.8 and finished with 11.2. I don't think I've ever had above 17 in a balanced, up and down, section of road.

 

18-22mpg here; mixed city & highway. Hovers around 19mpg over the last 1000mi. If I drive more aggressively, that’ll drop to 18ish. Did right about 20 on a round trip from Ohio to Florida & back, which was mostly highway and 75mph or so. This is on an ‘18 used as a daily driver, mostly unloaded, with 39,000mi and no mods other than air intake. I don’t drive my truck hard. If you want to save fuel, you’ve got to drive like you want to save fuel.

 

2020 Silverado
23,500 miles on truck mileage computer from day one 16.2 mpg

Last 5000 miles 15.5 average


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2020 Silverado
23,500 miles on truck mileage computer from day one 16.2 mpg

Last 5000 miles 15.5 average


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That’s incredible. How is that possible? My calculated average over 15,000 miles is 11.something.

 

First off, what units are everyone using on the lie o meter??? What’s done to the truck?? Larger tires etc??

I only have 4500km on this truck on stock rubber. My lie o meter set up at a 50km average got a best of 8.8l/100km. Hand calculated on The same trip it was 24mpg Canadian units used. This truck so far is the best diesel on fuel I’ve owned to date. I can easily get over 1100km on a tank of fuel.
So doing the math for all of you. 24imperial mpg is 20 US mpg.


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First off, what units are everyone using on the lie o meter??? What’s done to the truck?? Larger tires etc??

I only have 4500km on this truck on stock rubber. My lie o meter set up at a 50km average got a best of 8.8l/100km. Hand calculated on The same trip it was 24mpg Canadian units used. This truck so far is the best diesel on fuel I’ve owned to date. I can easily get over 1100km on a tank of fuel.
So doing the math for all of you. 24imperial mpg is 20 US mpg.


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If you want to track fuel economy, it might be useful to use one of the trip meters and reset it each time you fill the tank. (it rests both the trip distance and the trip fuel economy)
And if a long term log is desired, record the trip meter numbers and fuel added at each fill.

(I set the 2nd trip meter so it doesn't display so it doesn't accidently get reset. It then keeps track of 'life of vehicle' fuel economy)

I often have one (the 31mile / 50km one) of little best/average/instantaneous pages up to get an idea how mileage changes with driving conditions. ('inch' unit trucks have a 25 mile one)
The 'average' and 'instantaneous' give an idea how current usage compares with the usual tank averages.

imho, the 'best' numbers are of passing interest as they are typically obtained under conditions that may not be often repeated.

 

I'm just finishing a trip from wisconsin to texas and back. The 1200ish miles to texas averaged at 19.8mpg. Today on the way back I've got 530 miles to go I'm at 20mpg. Truck has about 12300 miles on it. I'm on the third oil change. The truck has regen 3 times so far for both legs. I'll probably force a regen right before I get home if it's close to 90% or above as I have a bunch of short trips later this week.

My highway mileage has greatly improved in the last 5000 to 6000 miles. I'm ok with getting 17 to 20 mpg as my old truck struggled to get 13 unloaded

Try using your cruise control more

 

My 2021 with 9,000 miles delivers:

around town 11-13 pulling 4k lbs enclosed trailer
Hwy steady 70 mph unloaded 19-20
Hwy steady 80 mph unloaded 16-17

Stock with fiberglass cap

Around town it’s about the same as my 2014 5.0 F150. On the hwy, the Duramax delivers about 30% better fuel economy…….at higher speeds it approached 40%.

For the power, comfort and capabilities, my expectations have been exceeded.

It operates in all conditions with much less effort than the F150 (which is a good truck).


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I experienced absolutely the same issue.

I sold my 2015 which would easily get 15 around town and 20 MPH on the highway.

Picked up a 2021 with 70 miles on the odometer. No matter what I couldn't get more than 12 MPG on the highway. I spoke to a diesel tech and he said you need to get at least 3-5 K on the engine before he mileage comes up. Once I hit 3500 K it started to increase and then once I hit 5K I was able to get near 20 MPG on the highway.

One thing I've come to realize is this truck has a very light pedal (very sensitive to driving style). So it's really easy to burn extra fuel when you don't need it. I've found it helpful to to display the instant fuel economy which helps me keep my foot of the floor.

 

I have a 2020 Z71 3500 Single rear wheel, stock completely.
I just changed the oil today with 7100 miles and the average over those miles was 19.7mpg.
Towing my trailer last week into the mountains for hunting Average was 13.5mpg
Driving to Corvallis OR from Beaverton OR on I5 I average 23mpg. 70-75mph
Most of the miles on my truck are Highway miles and very little city driving. 19000 miles so far.
Usually get 20-23 on the highway and 17-18 in town.

 

I have a 2022 Silverado 2500HD with 1719 miles. I'm averaging between 17 and 18 mpg with combination freeway and city stop-and-go driving. This based on calculations from weekly fill ups and mileage records. I use a light foot. That truck will take off on you if you don't pay attention; the next thing you know you ! This is about what I was getting with my old 2017 Silverado 1500 LTZ 6.2L on Premium gas under the same circumstances. The best I have gotten is just under 20 mpg freeway driving. Engine is still settling in.

 

Purchased my truck with 19k and the Trip 2 had never been reset and it it was on 18mpg. I now have 30k and trip 2 is down to 15.8. I don’t think the first owner ever pulled with it. Of my 11k miles owning it I have drove all
Over AK camping and then from AK to AZ pulling the sample camper. Our trip from AK to AS my avg was 10.8.

My best hand calculated was 20.5.

I too have found the the gauge in the truck is far from accurate. I track all fill-ups using Fuelly and I find the gauge is 1.5-2.5 mpg better than hand calculated.

 

So just for fun I did a little road trip comparison. 429 miles one way from southern New Jersey to grand island New York. I ran an average speed of 73mph. Up hills down hills, ran cruise control as much as possible. My truck is a 2021 crew cab standard bed, z71 with 15000 miles on it. Only thing I changed on the truck was I blocked off the intake resonator, wrapped the intercooler pips with head wrap and I poured two 8ounce bottles of opti lube XPD fuel additive. Going by their recommendations of 8 ounces to 20 gallons, I know it’s not a 40 gallon tank but I figured that little extra won’t hurt. A ton of people say that it will harm the truck and it will make the truck run more regen cycles. When I drive 1 mile down the road to fill up on fuel and DEF fluid. I will report back the mileage and how much DEF it burned. On my ride home I won’t put any fuel additive in and will compare the results. I run only the Valvoline DEF fluid for less variables in the test. I left NJ at 1pm today and got to grand island NY at 740. I will be leaving the hotel at the same time to help keep the temperature and traffic the same. Hopefully 🙏🏻

 

I figured I’d chime in. Bought my truck, 2022, Silverado 2500hd high country z71 completely stock, with 18,500 miles on it. I’ve put about 2k miles in the last 3 weeks.

2 weeks ago I did a round trip from Houston to San Antonio unloaded. Mostly flat terrain and I had my cruise control set to 85mph for at least 80% of the trip. Over 400 miles and just under 18mpg.

 

I figured I’d chime in. Bought my truck, 2022, Silverado 2500hd high country z71 completely stock, with 18,500 miles on it. I’ve put about 2k miles in the last 3 weeks.

2 weeks ago I did a round trip from Houston to San Antonio unloaded. Mostly flat terrain and I had my cruise control set to 85mph for at least 80% of the trip. Over 400 miles and just under 18mpg.

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Did you happen to do a hand calculation alongside this? The guys with newer trucks are saying the DIC calculated fuel economy is finally getting closer to the hand calculated. I'm curious what your observations are.

My 2017 is off around 1mpg consistently. The lower my actual economy is, the closer the DIC and hand calc are, which is interesting to me.

 

I've ask this question many times, no rational answer. Why would hand calculating mileage make a difference? There are only 2 variables to consider: Miles and gallons. Which one, or both, are incorrect in the truck's calculation?

 

What are you asking? Are you asking why people want to know the hand calculated MPG vs DIC MPG? If that’s the case, it’s because the DIC is wildly inaccurate, contrary to what @Melonhead1102 says above. My truck is always optimistic, sometimes up to 1.5 mpg, so yes, hand calc vs DIC there is a big difference. That’s why guys ask what the hand calc mpg is. As far as which on is incorrect in the truck, the gallons is incorrect.

 

My lifetime MPG is 10.7, and yes, hand calculated.

 

If you use a calculator is it still considered hand calculated?

 

You push the buttons with your fingers right?? 😂