What did Chevy do to ruin a perfectly good engine? I had a 2020 and was getting 18mpg mixed fuel mileage. My new 2025 with same engine, transmission and rear end is getting 14.5 with same driving habits. DId the EPA make them choke these motors down even more? BTW, my 2020 was getting better than 18 mpg until they did a recall and flashed the ECM.
reelmagic
The engine isn’t the same.
They get what they get. They’re not rated by the EPA and they tend to vary from one truck to the next. If it hauls and tows the loads that you have and gets work done I wouldn’t really worry about it.
They get what they get. They’re not rated by the EPA and they tend to vary from one truck to the next. If it hauls and tows the loads that you have and gets work done I wouldn’t really worry about it.
My 2022 truck took about 10,000 miles before mileage improved.
Plus more power equals more fuel usage. Power comes from somewhere.
Plus more power equals more fuel usage. Power comes from somewhere.
While a completely different drivetrain, my LMM mileage didn't improve until I got about 20k on the truck.
The mileage on my L5P is about the same as yours but I only have 16k on it right now. Hope that it gets better with more miles on the truck.
The mileage on my L5P is about the same as yours but I only have 16k on it right now. Hope that it gets better with more miles on the truck.
Pretty sure they retarded the timing on the new ones (they also regen more) and thus lowered NOx with lower combustion temps from retarded timing. More smoke and less FE from retarded timing, BUT less NOx.
The 'update' on the 2020's was likely the same. Retarded timing for a NOx reduction.
I have not updated my 2020.
The 'update' on the 2020's was likely the same. Retarded timing for a NOx reduction.
I have not updated my 2020.
As has been said, "More Power = Less MPG" - you should read these threads over on the ford-trucks forum 
Ford (and RamCummins) offer a "High Output" version of their respective oil burners. It's entertaining to watch the guys with HO engines arguing their point that the 1-2 mpg hit on mileage is "totally worth it!" for the extra power.
I've noticed my new truck does regenerate the DPF far more often than my last two L5P's (2020 and 2022) - I see the telltale grey smoke about every 200 miles now, but it seems to last about 10-15 miles at most. I would expect the more frequent regen is impacting overall MPG.
The "More Power = Less MPG" rule mostly holds true under modern emissions rules. To John's point above, yes without concern for soot and NOx these modern engines should be improving their fuel economy. The issue is that more power, coupled with tighter emissions requirements, generally equals lower overall fuel (and DEF) economy.
Here is how I console myself of the grief of loosing a few MPG (and burning more DEF) --- I tell myself, that for as long as I live in Washington state, this may be the last oil burner I get the privilege to own. Between EV mandates and Blue state CARB rules, my choices in the future will be limited to whatever those in authority allow me to buy. My wife does like the Silverado EV, which might be the only thing I can buy with a truck bed in the future... The forbidden fruit tastes all the more sweeter....
Ford (and RamCummins) offer a "High Output" version of their respective oil burners. It's entertaining to watch the guys with HO engines arguing their point that the 1-2 mpg hit on mileage is "totally worth it!" for the extra power.I've noticed my new truck does regenerate the DPF far more often than my last two L5P's (2020 and 2022) - I see the telltale grey smoke about every 200 miles now, but it seems to last about 10-15 miles at most. I would expect the more frequent regen is impacting overall MPG.
The "More Power = Less MPG" rule mostly holds true under modern emissions rules. To John's point above, yes without concern for soot and NOx these modern engines should be improving their fuel economy. The issue is that more power, coupled with tighter emissions requirements, generally equals lower overall fuel (and DEF) economy.
Here is how I console myself of the grief of loosing a few MPG (and burning more DEF) --- I tell myself, that for as long as I live in Washington state, this may be the last oil burner I get the privilege to own. Between EV mandates and Blue state CARB rules, my choices in the future will be limited to whatever those in authority allow me to buy. My wife does like the Silverado EV, which might be the only thing I can buy with a truck bed in the future... The forbidden fruit tastes all the more sweeter....
Does everybody understand that at unloaded cruise your only using 80-100hp of the available 450-500hp?
My old dodge with 160hp got about 17-18mpg. My 2020 with 450hp gets 17-19mpg.
Its the tune (engine efficiency tied with meeting emissions) that matter when displacement, cylinder fill efficiency and . Of coarse tire size, wind resistance, weather are all factors as well.
My old dodge with 160hp got about 17-18mpg. My 2020 with 450hp gets 17-19mpg.
Its the tune (engine efficiency tied with meeting emissions) that matter when displacement, cylinder fill efficiency and . Of coarse tire size, wind resistance, weather are all factors as well.
L5P output changed in 2024
2023
L5P Engine, Duramax 6.6L Turbo-Diesel V8, B20-Diesel compatible, (445 hp [332 kW] @ 2800 rpm, 910 lb-ft of torque [1220 Nm] @ 1600 rpm)
2024
L5P Engine, Duramax 6.6L Turbo-Diesel V8, B20-Diesel compatible, (470 hp [350.5 kW] @ 2800 rpm, 975 lb-ft of torque [1322 Nm] @ 1600 rpm)
2023
L5P Engine, Duramax 6.6L Turbo-Diesel V8, B20-Diesel compatible, (445 hp [332 kW] @ 2800 rpm, 910 lb-ft of torque [1220 Nm] @ 1600 rpm)
2024
L5P Engine, Duramax 6.6L Turbo-Diesel V8, B20-Diesel compatible, (470 hp [350.5 kW] @ 2800 rpm, 975 lb-ft of torque [1322 Nm] @ 1600 rpm)
If you live in a cold climate like I do, the diesel fuel provided at the pumps is number 1 diesel. This typically starts November 1 where I live. It burns hotter and faster and you will get lower mileage. I'm probably telling you something you already know but maybe you weren't considering that when you noticed the difference in mileage. Cheers
Define straight #1 diesel because I never said straight or anything to establish the percentage of #1 to #2 mix. All I know is, the pump says #1 diesel. The fact is, ANY amount of #1 diesel used will affect mileage. That has been my experience and I looked it up to verify why this is the case.
"2-D fuel performs well in high-temperature environments due to its thin consistency. At the same time, it is prone to freezing. Similarly, 1-D fuel is well-known for having lubricants and detergents within its makeup, but 2-D fuel may provide better fuel efficiency in the warmer months.
Knowing the benefits of different grades of diesel fuel helps you to strategize throughout the year. In fact, #1 and #2 diesel fuels can even be combined to give drivers the best of both worlds." -SC Fuels
"2-D fuel performs well in high-temperature environments due to its thin consistency. At the same time, it is prone to freezing. Similarly, 1-D fuel is well-known for having lubricants and detergents within its makeup, but 2-D fuel may provide better fuel efficiency in the warmer months.
Knowing the benefits of different grades of diesel fuel helps you to strategize throughout the year. In fact, #1 and #2 diesel fuels can even be combined to give drivers the best of both worlds." -SC Fuels
Thanks for making my point again. Now, what is your point besides the typical keyboard warrior trolling that you are becoming famous for?
The pump says #1 diesel, so your "point" is lost on me. I am trying to give usable information and you are being yourself...again...move on Hoser.
The pump says #1 diesel, so your "point" is lost on me. I am trying to give usable information and you are being yourself...again...move on Hoser.
You are stating that winter diesel is #1 diesel, per your post above. Just because #1 is “provided” at the pump, that doesn’t mean it should be considered winter diesel and used exclusively. I can buy #1 diesel year round. I personally have never seen only #1 diesel provided at the pumps like you said in your post.
It may be provided at the pump so that you can do your own blending of it with #2. Or, if you are in an extreme cold region, you can run straight #1, but that is pretty rare which is why I was wondering where you were that you were running straight #1 diesel.
The vast majority of diesel is winterized per region, and most truck stops will even do some winterizing to diesel in southern regions since it’s likely that customer will travel north into a cold region.
Winterized diesel is fuel with specific additives and depending on the time of year and region, it will be blended with #1 diesel. But unless you are well below -0°F for most of the season, it’s not recommended to use straight #1.
I don’t know what I did to hurt you in the past, but I’m sorry.
It may be provided at the pump so that you can do your own blending of it with #2. Or, if you are in an extreme cold region, you can run straight #1, but that is pretty rare which is why I was wondering where you were that you were running straight #1 diesel.
The vast majority of diesel is winterized per region, and most truck stops will even do some winterizing to diesel in southern regions since it’s likely that customer will travel north into a cold region.
Winterized diesel is fuel with specific additives and depending on the time of year and region, it will be blended with #1 diesel. But unless you are well below -0°F for most of the season, it’s not recommended to use straight #1.
I don’t know what I did to hurt you in the past, but I’m sorry.
Fair enough, my experience has been that #1 diesel shows up at the pumps here in Nebraska on Nov 1 and that is what we get until Spring. I am not sure if it is straight or if it a blend of the two.
Apology accepted, I apologize as well if I misjudged you, peace.
Apology accepted, I apologize as well if I misjudged you, peace.
My second oil change I went Rotella T6…. The engine was NOT broken in…!! Soon started “using” oil… more and more.. so, went with stock oil from GM… the oil consumption settled to 1/2 qt towing per 4k miles… better than 1 qt per 6-700 (GM states 1qt to 500 miles is “normal”….)
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