2025 Cummins MPG Compilation

[NewBlackDak]

About to do my 4th fillup. Most of my miles have been towing in the 14-17Klb range, or driving in the mountains.

Whitey (Ram 3500) | Fuelly

 

[PyroJoe]

I finally beat 20mpg today! Averaged 22.5mpg over 115 miles and 20.8mpg over 286 miles. The key is most definitely that 1350 RPM ballpark. Set my cruise on 56mph and let it do its thing. The other motorists weren't pleased but I was ecstatic!

Also made a video documenting the whole trip:

 

[HarryN]

I finally beat 20mpg today! Averaged 22.5mpg over 115 miles and 20.8mpg over 286 miles. The key is most definitely that 1350 RPM ballpark. Set my cruise on 56mph and let it do its thing. The other motorists weren't pleased but I was ecstatic!

Also made a video documenting the whole trip:

View attachment 88806

So - just for fun - if nothing else changed except the tire diameter, what would the theoretical mpg be ?

 

[PyroJoe]

So - just for fun - if nothing else changed except the tire diameter, what would the theoretical mpg be ?

I will let you know when I slap these 35's on in a week or 2. I imagine max mpg will drop by 2.5-3 and daily will drop by 1.5-2.

 

[MacksRam]

-2500
-4x4
-Tire size--18" stock Firestone
-Crew Cab
-Odometer--2100 miles on truck when left home.
-Avg speed--75-80 MPH on the interstate-- drove 390 miles total.
Was NOT pulling a trailer--had approx 1500lbs in the bed.
I did hand calculation on 2 tank fill ups----1st tank--18 MPG, 2nd tank--17.8
(dash read out was showing about 1 MPG more than it was really getting)

 

[aogmitch]

Did a trip from Washington to Arizona last week with camper and trailer loaded with the maxima. These are my results. I reset my trip A meter every fill up and truck is still reading close to hand calculations. The one tank that got 8.4 mpg was through eastern Oregon (hilly) and Idaho (speed limit 80, so was mostly driving at 85+).

 

[56ram2500]

Did a trip from Washington to Arizona last week with camper and trailer loaded with the maxima. These are my results. I reset my trip A meter every fill up and truck is still reading close to hand calculations. The one tank that got 8.4 mpg was through eastern Oregon (hilly) and Idaho (speed limit 80, so was mostly driving at 85+).

Question how do you know that the Cetane was 45 for all of the diesel you bought? I did a short drive 4454 miles this summer to the Midwest an never one did I see the Cetane listed on any diesel pump....

 

[aogmitch]

I didn’t. Just showing up that way since I selected that on my very first log. These are the options given when diesel is selected in the Fuelly app.

 

[56ram2500]

I didn’t. Just showing up that way since I selected that on my very first log. These are the options given when diesel is selected in the Fuelly app.View attachment 89858

Ok, got it, fyi we are lucky if our diesel is over 40 Cetane, they claim with 5% bio it should be over 40 but I have yet to see anyone show proof that it is, I'm excluding commie California as I don't have a passport to allow me and my truck go to that state, thus I have no idea what they sell...

 

[MacksRam]

Quick update on MPG:
I just completed pulling my 22-foot Travel Trailer 1600 miles over 3 days. From Mississippi to Grand Canyon Arizona. The RV weighs approx. 6200LB. I averaged a speed of approx 75 MPH. For the entire trip I averaged 10.1 MPG--this is HAND CALCULATED.
(Honestly I am a little disappointed--I would say this is about 1-2 MPG less than my previous 2017 Ram 2500 Cummins. But I would guess that the 2025 will get better MPG when I get more miles on it---currently has 5000 miles on it)

 

[PyroJoe]

Quick update on MPG:
I just completed pulling my 22-foot Travel Trailer 1600 miles over 3 days. From Mississippi to Grand Canyon Arizona. The RV weighs approx. 6200LB. I averaged a speed of approx 75 MPH. For the entire trip I averaged 10.1 MPG--this is HAND CALCULATED.
(Honestly I am a little disappointed--I would say this is about 1-2 MPG less than my previous 2017 Ram 2500 Cummins. But I would guess that the 2025 will get better MPG when I get more miles on it---currently has 5000 miles on it)

But what are your truck specs??

 

[MacksRam]

But what are your truck specs??

Sorry about that Mr PyroJoe,
2025 Ram 2500 6.7L Bighorn Cummins Crew Cab 4WD. 100% stock. 3:42 rear end, Stock 18" wheels with stock Firestone Transforce H2 road tires, I am adding Power Service Diesel Kleen (silver jug) to each tank of diesel, I am running Blu Def Platinum DEF.

Side Note: The truck performed great for the entire 1600-mile pull---I have been driving NOTHING but Ram Cummins trucks for 25 years--this is my 5th Ram Cummins. You can tell it has a LOT of torque, but when you "call on it" pulling up a hill---it likes to drink the fuel )

 

[PyroJoe]

Sorry about that Mr PyroJoe,
2025 Ram 2500 6.7L Bighorn Cummins Crew Cab 4WD. 100% stock. 3:42 rear end, Stock 18" wheels with stock Firestone Transforce H2 road tires, I am adding Power Service Diesel Kleen (silver jug) to each tank of diesel, I am running Blu Def Platinum DEF.

Side Note: The truck performed great for the entire 1600-mile pull---I have been driving NOTHING but Ram Cummins trucks for 25 years--this is my 5th Ram Cummins. You can tell it has a LOT of torque, but when you "call on it" pulling up a hill---it likes to drink the fuel )

Wow, so this just adds to my theory. Your 2500 should get worse mileage than my 3500 since your tires are much taller, plus you're towing a heavier trailer, but yet we both average about 10mpg.
As for the "power" - I think the transmission tuning is lacking. It seems to hang this engine out to dry before it'll shift, just like the 47RH/RE did. Wish it'd shift a couple hundred RPM sooner.

 

[MacksRam]

Wow, so this just adds to my theory. Your 2500 should get worse mileage than my 3500 since your tires are much taller, plus you're towing a heavier trailer, but yet we both average about 10mpg.
As for the "power" - I think the transmission tuning is lacking. It seems to hang this engine out to dry before it'll shift, just like the 47RH/RE did. Wish it'd shift a couple hundred RPM sooner.

Concerning Tranny shift points: IF you start off easy on the throttle--the tranny shift points are at a lower RPM (even when I pull the Travel trailer). BUT if you lay into the pedal from a stop--yes, the shift points are delayed at a higher RPM.
Lot of points to make here but 1 good point about higher RPM/delayed shifts points is higher transmission oil pressure which means it is holding the clutch plates tight so there is a less likelihood of tranny slippage or Torque Converter slippage (I have dealt with this issue on previous trucks). This is very important if you are pulling a heavy load. As you know a 6200lb Travel trailer is actually a light load for this truck.

 

[HarryN]

Quick update on MPG:
I just completed pulling my 22-foot Travel Trailer 1600 miles over 3 days. From Mississippi to Grand Canyon Arizona. The RV weighs approx. 6200LB. I averaged a speed of approx 75 MPH. For the entire trip I averaged 10.1 MPG--this is HAND CALCULATED.
(Honestly I am a little disappointed--I would say this is about 1-2 MPG less than my previous 2017 Ram 2500 Cummins. But I would guess that the 2025 will get better MPG when I get more miles on it---currently has 5000 miles on it)

It will be interesting to see if you pick up some mpg when going back downhill to Mississippi.

 

[MacksRam]

It will be interesting to see if you pick up some mpg when going back downhill to Mississippi.

HarryN,
All joking aside, it will likely get better MPG on the way home! I will try to remember to post this update when I get home...
I noticed starting around Amarillo, TX--we were continuously climbing in elevation all the way to Grand Canyon. I could tell the truck was pulling harder starting at Amarillo. Nothing major, but it was much quicker to downshift to 7th gear. Of course, that Cummins has teeth out front ....

 

[MacksRam]

HarryN,
All joking aside, it will likely get better MPG on the way home! I will try to remember to post this update when I get home...
I noticed starting around Amarillo, TX--we were continuously climbing in elevation all the way to Grand Canyon. I could tell the truck was pulling harder starting at Amarillo. Nothing major, but it was much quicker to downshift to 7th gear. Of course, that Cummins has teeth out front ....

Final update:
We got home Saturday (10/04/2025) evening. Total trip mileage was 4000 miles.
Unfortunately, the MPG averaged the same 10.1 MPG on the way home. Meaning I-40 from Amarillo, TX to Mississippi. There again I was averaging 72 to 75 MPH pulling a 22-foot Travel Trailer (6200 LBS). Truck is completely stock with stock 18" factory aluminum wheels and 18" Firestone Transforce HT2 tires.
I am sure if I had dropped my speed down to 55-60MPH--the MPG would have been better..
Also, as mentioned on the other thread--TOTAL DEF Fluid usage for the 4000-mile trip was 10 gallons (Blu Def Platinum).

 

[DarkHorse8]

Final update:
We got home Saturday (10/04/2025) evening. Total trip mileage was 4000 miles.
Unfortunately, the MPG averaged the same 10.1 MPG on the way home. Meaning I-40 from Amarillo, TX to Mississippi. There again I was averaging 72 to 75 MPH pulling a 22-foot Travel Trailer (6200 LBS). Truck is completely stock with stock 18" factory aluminum wheels and 18" Firestone Transforce HT2 tires.
I am sure if I had dropped my speed down to 55-60MPH--the MPG would have been better..
Also, as mentioned on the other thread--TOTAL DEF Fluid usage for the 4000-mile trip was 10 gallons (Blu Def Platinum).

I’m a high speed tower myself. I don’t blame you.

 

[WXman]

Those of you who went from a 6-speed Cummins to this new 8-speed Cummins, do you feel that the new truck truly gets better MPG? OR about the same?