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Hello Everyone! I just picked up my 2021 Sierra 1500 AT4 with the LM2 Line 6. I have put 900 miles on it and the best fuel economy I have achieved is still below 25 mpg on the highway. Full disclosure, I'm in Alaska and the temps have been hovering around zero consistently, but even with using Diesel #1 up here, I still figured I'd be able to achieve higher numbers than that. I had an 09 6.6l sierra that I could get 24mpg out of on the Highway, and my 328d BMW gets a whopping 44+ mpg on the highway in the summer, and as high as 40mpg on the highway in winter driving. What is everyone else getting on their LM2 engines? And yes, I'm driving it SUPER EASY and still not getting anything near the EPA ratings.
 

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Mixed driving I’m getting 22mpg, I haven’t done a hwy only tank yet. I think it’s the winter blend keeping your mileage around 25. Did you hand calculate your mileage? The computer seems to always read lower then actual mileage from what I’ve seen others say and from what I’ve experienced in my short 700 miles.

Also the epa rating for a 4wd is 27 if I remember, 2wd was 30 if I remember correctly, you have the at4 which may also reduce mileage with the slight lift on it but 25 isn’t far off for a 4wd.

Also mileage should increase once the engine is broken in, maybe around 10k miles.
 

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EFFICIENT YET CAPABLE
Diesel engines are often recognized for their capability and grit to tow, as well as their driving range and fuel economy.
And the Duramax 3.0L Turbo-Diesel is no different. With up to 30 MPG highway, this powertrain offers you the most efficient Sierra 1500 ever. That’s because it was engineered to include multiple advanced combustion technologies to bring about high levels of efficiency, helping you spend less time and money at filling stations and more time getting to where you want to go.
FUEL EFFICIENCY

MODEL
CITY
HIGHWAY
COMBINED
TWO-WHEEL DRIVE
23 MPG
30 MPG
26 MPG
FOUR-WHEEL DRIVE
22 MPG
26 MPG
24 MPG
 

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I suppose every truck is different. The computer calculated MPG in my truck is surprisingly close to my manual calculations. I have a 2WD and most of my driving is on East Texas country roads. Tempurature's been in the 40's and 50's lately. My mileage has been between 26 and 33 in the 2500 miles I've had the truck.
 

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I just reset my trip odometer and it read 20.1 for 520 miles. At only 1800 miles on it, and it being winter, I don't expect more yet. Not a lot of long trips, mostly 16 miles to work (both highway and city streets). These colder temps coming up in the next two weeks will only make it go down. Once we get off winter blend and the temps rebound, I expect to see a significant increase like I did on my 2.8 Colorado.
 

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Just completed a 3300 mile round trip. 26 average mpg. Best 29,worst 24. Speed between 73-80 mph took a toll on mpg. 65-73 resulted in best. Driving was 25% hilly and 75% flat cruising, all highway. Very happy with results.

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2022 Silverado Z71 LT crew cab 4x4 3.0 Duramax
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I’ve had the truck a year. Right now there is 27k+ on it. The mpg calculator on the odometer that hasn’t been touched is at 26.7 mpg. My all time best is 39.1. Right now my mileage is down with the winter blend fuel, but with an 1 1/2 hr drive to work on highways going 55 halfway,then 70 the other half, I’m still average over 28 mpg a day. I also think my truck has a slight air leak at boost so I’m sure that’s not helping.
 

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I’ve had the truck a year. Right now there is 27k+ on it. The mpg calculator on the odometer that hasn’t been touched is at 26.7 mpg. My all time best is 39.1. Right now my mileage is down with the winter blend fuel, but with an 1 1/2 hr drive to work on highways going 55 halfway,then 70 the other half, I’m still average over 28 mpg a day. I also think my truck has a slight air leak at boost so I’m sure that’s not helping.
What makes you think you have a leak? Sound or seeing it on a gauge?
 

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2022 Silverado Z71 LT crew cab 4x4 3.0 Duramax
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Sound. I can hear it under boost. As soon as I let off it goes away. Maybe it’s in my head, but I don’t remember hearing it before. I’m going to call the dealer to check it out.
 

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Sound. I can hear it under boost. As soon as I let off it goes away. Maybe it’s in my head, but I don’t remember hearing it before. I’m going to call the dealer to check it out.
The reason I ask is that since I bought my truck, the sound under acceleration has gone up. I’ve heard it described as a roar...mine is very similar. Not so bad in the morning but much louder when warmed up. I need to check the clamps since I’ve also heard that they can be loose from the factory. Too damned cold to do that now so it’ll have to wait.
 

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I just have 1500 miles on my truck so I don't have a whole lot of mileage data to share. But I'm seeing just under 19 MPGs so far with mixed city/highway. Probably slightly more towards city, like 60-65%. I've got winter blend fuel working against me (I'm in NY) and some idle/warm up time in the morning. Typically not much more than 5 mins. I'm hoping it comes up a lot come summer, but I know being an AT4 with Duratracs it certainly won't be leading the pack for mileage.

Sound. I can hear it under boost. As soon as I let off it goes away. Maybe it’s in my head, but I don’t remember hearing it before. I’m going to call the dealer to check it out.
Do you have something like a Banks iDash or other OBD2 reader that can monitor boost? From monitoring mine, it seems to peak at around 28 psi.
 

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The reason I ask is that since I bought my truck, the sound under acceleration has gone up. I’ve heard it described as a roar...mine is very similar. Not so bad in the morning but much louder when warmed up. I need to check the clamps since I’ve also heard that they can be loose from the factory. Too damned cold to do that now so it’ll have to wait.
I have noticed the same issue..it appears due to the extreme cold..and the fuel combination the engine is not getting the cetane as smoothly as needed

These insights might help..

Quotes

Winterized diesel fuel

Winterized diesel fuel is a combination of #1 and #2 fuels that, when blended together, holds a higher concentration of #1 grade diesel fuel. These fuels are used during the months when it becomes too cold to use #2 grade.

The combination of both grades of fuel should contain enough energy components and lubricant properties to reduce the chance of the chemical mix gelling in colder temperatures. Typically, the fuel economy drops slightly during the winter months because the demand for it is less than at other times of the year.

Using #1 grade diesel fuel in the winter should never cause any immediate concerns. However, prolonged use in engines that are specifically-designed for #2 grade may reduce engine life span over a long period of time. #1 and #2 grade fuels can be mixed at the same time. This means you don’t have to worry if #1 grade is only available during the winter months.


What is the difference between Diesel Fuel Supplement +Cetane Boost and Diesel Kleen +Cetane Boost?
Diesel Fuel Supplement +Cetane Boost (in the white bottle) is a winterizer/antigel for use when temperatures drop below 30°F. for winter operability. Diesel Kleen +Cetane Boost (in the silver bottle) is an injector cleaner and performance improver for use when temperatures are above 30°F. Use our seasonal tip to help remember which product to use: “White for winter, silver for summer.”

I have used both Standyne and Diesel Kleen and have "smoother" shifts and quieter engine with Diesel Kleen. I will never run this engine without either..it becomes too harsh

Nice Ohio Weather..
 
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