Is my Truck Defective??

[Hatche90]

I have a 2021 1500 with a 3.0 Duramax and my mpg’s seem lower than most. I’ve always averaged 17 miles per gallon from daily commutes. My daily commutes are usually 7 miles from point A to point B. I live in Colorado, so I’m thinking that the higher altitude might be a reason for the low mpg’s. The highest mpg I’ve gotten is 22 mpg and that’s from when I make a trip from Colorado Springs to Denver. I use Hot Shot fuel additives on Every fill up and my tires are Toyo Open Country 305/55R20.

My “performance” mods are a Stillen air scoop, drop in K&N air filter, modified stock air box, 3 in air intake tube, and turbo resonator delete.

My thoughts are that the tire size and high altitude could be the cause of my less than average mpg’s. What are you’ll thoughts?

 

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[grover]

how many miles on it?

 

[Hatche90]

how many miles on it?

As of today it has 56k

 

[Chopper_Man]

truck isn't even getting to full temp on a 7 mile commute. That's what's killing the economy.

 

[Hatche90]

truck isn't even getting to full temp on a 7 mile commute. That's what's killing the economy.

What do you mean be full temp? Are you suggesting that it needs to be remote started minutes before driving it? If so, then I am allowing the truck to run for 15 minutes prior to driving it. However, I could kind of see this as a reason that the mpg’s might be lower than usual.

If you are referring to getting in the truck with a cold engine and then not driving it long enough to allow the engine temp to come up to normal then I can see that point. However, I guess at that point I’d have to consider the pros and cons of low mpg’s on a light commute with less wear and tear and less mileage racked on the odometer or higher mpg’s with a longer commute, more wear and tear on the vehicle, and put more mileage on the vehicle.

Something else that doesn’t explain this lower milrage than a typical 3.0 Duramax is why is my highest mpg’s at 22 on a commute that definitely had the engine warmed up to temp. I would expect that number to be higher by a minimum of 5 mpg’s.

In short, my mpg’s are not only lower that expected in short commutes, but they are also lower than expected in long commutes (example: Colorado Springs, Colorado to Cheyenne, Wyoming (2 hour drive each way) and from Colorado Springs to San Antonio, Tx (13 hour drive each way))

 

[ironworker40]

15 minutes of warm up then drive 7 miles for say 15 more minutes. So half of the time your engine is running you are getting 0 MPG. I'm surprised its as high as 17. Have you hand calculated it to check the dash MPG's to see if it's correct? They are known for being very generous. What is your altitude?

 

[Hatche90]

15 minutes of warm up then drive 7 miles for say 15 more minutes. So half of the time your engine is running you are getting 0 MPG. I'm surprised its as high as 17. Have you hand calculated it to check the dash MPG's to see if it's correct? They are known for being very generous.

I have hand calculated the mileage and it was nearly the same as what the dash states.

 

[Viking Truck]

I did not have my 2015 very long before I put 305 55R20 on it. I firmly believe they wrecked my fuel economy even though I did not have a lot of experience with it I upgraded the tires.

 

[ironworker40]

I have hand calculated the mileage and it was nearly the same as what the dash states.

Then you're lucky on that. I have never had one that was correct.

 

[Hatche90]

I did not have my 2015 very long before I put 305 55R20 on it. I firmly believe they wrecked my fuel economy even though I did not have a lot of experience with it I upgraded the tires.

The tires came new on the truck when I bought it, but immediately assumed they would lower the fuel mileage. I just wasn’t sure how big of a hit.

 

[Teegunn]

Your tires are probably about an inch taller than the stock tires, so you need to take that into consideration when figuring MPG. I always find out the revolutions per mile of the stock tires, the bigger tires, then figure that difference in to what the actual MPG are. You have more tire surface on the road with the wider tires vs stock, plus the bigger tires are a bit heavier. This will lower MPG.

My 2020 AT4 3.0 I had 305/55 R 20 Nitto RG's on it. I got about 17 MPG all around average, but I am a contractor and pull job trailers. Plus I live in Montana at 6100 ft elevation, and have 8 months of winter type weather most years, so that effects things also. Have to take into consideration all things.

On the whole, my 3.0 duramax got 3 to 5 MPG better than my 6.2 gasser in my 2023 ATX. But diesel costs more per gallon, plus DEF and more expensive oil changes, etc. I feel the out of pocket savings was not enough to worry about on MPG with the 3.0 duramax vs the 6.2 gasser. Plus the DEF and emissions system ended up with a constant "service emissions system" error code which put the truck into severe limp mode. I was still under factory warranty and they couldn't fix it after a month in the dealership shop, so I traded it off for my 23 AT4X. Liked the 3.0 duramax, but at the end of the day, the complicated emissions system forced me to get rid of it.

 

[R467X]

I don't think your MPG is horrible. Do you track regens? Are you running stock filtration? When's the last time you changed your filter?

I used to run hot shot and it's garbage. consider using the XPD one and see if that helps. My Regen times have gone significantly up and so has my MPG.

My HD alao gets horrible MPG if I drive around town, probably closer to 10. Soon as I hit the freeway it goes up to near 20 if there's no traffic and flat land.

You may also want to run a full diag scanner and see if any codes pop up. You could have something going on that isn't enough to light up your check engine and what not that may be behind lower fuel economy as well.

 

[Hatche90]

I don't think your MPG is horrible. Do you track regens? Are you running stock filtration? When's the last time you changed your filter?

I used to run hot shot and it's garbage. consider using the XPD one and see if that helps. My Regen times have gone significantly up and so has my MPG.

My HD alao gets horrible MPG if I drive around town, probably closer to 10. Soon as I hit the freeway it goes up to near 20 if there's no traffic and flat land.

You may also want to run a full diag scanner and see if any codes pop up. You could have something going on that isn't enough to light up your check engine and what not that may be behind lower fuel economy as well.

Which filtration are you referring to?

 

[R467X]

Which filtration are you referring to?

Your diesel fuel filter

 

[Hatche90]

Your diesel fuel filter

I have a VSE Fuel Filter Kit on my truck and change out the filter’s when the dash shows the filter percentage at 30%.