Fuel Economy? - Dodge Cummins Diesel Forum
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post #1 of 24 (permalink) Old 01-17-2020, 02:08 PM Thread Starter
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Fuel Economy?

Hi Fellas I'm new to diesel engines and all this custom tuning etc....
I plan to buy a new or newer dodge 3500 6.7, add a small camper, and put half a million miles on it. I don't need speed or 0-60 in 3 seconds... just great fuel economy. I drive like a little old lady these days so my question is: What mods would get me there?

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Last edited by EatDirt; 01-17-2020 at 02:09 PM. Reason: kms to miles
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post #2 of 24 (permalink) Old 01-17-2020, 05:56 PM
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Leave it the way it is and see what you got. What mileage are you expecting?

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post #3 of 24 (permalink) Old 01-17-2020, 06:31 PM
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I have not heard of any mods to the newer 6.7 Cummins that translated into real world improvements to your fuel mileage. I get about 16 mpg in mixed driving. About 10 mpg pulling a 40 ft/16,500 lb 5th wheel.

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post #4 of 24 (permalink) Old 01-17-2020, 06:35 PM
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Buy a gasser?

The cost of any tunes or hard parts to increase mileage on a CTD will outweigh your fuel costs.

Different story if you're looking for more power/performance and/or lower EGT's when towing heavy.

If buying a new diesel and you don't need 1K lb-ft, get the SO for better bone stock mileage.

FWIW, I never took my own advice.
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post #5 of 24 (permalink) Old 01-17-2020, 07:18 PM
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Leave it stock.

Heres what I get.


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post #6 of 24 (permalink) Old 01-17-2020, 10:31 PM
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You've got to go back to a pre-DEF truck to be able to greatly improve MPG through delete and tune. Are you looking for SWR or DWR. If a SWR, you'll likely want to upgrade the rear suspension. Don't get one with factory air bags. They sit inboard of the springs which aggravates side-to-side rocking.

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post #7 of 24 (permalink) Old 01-17-2020, 11:39 PM
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There isn’t any evidence yet that the HO or SO get better or worse mileage. If in compatible trim. There is a thread running around on here that calls the SO the “efficiency motor.” I can’t roll my eyes hard enough. Made up crap someone feels better about.

See my signature fuelly stats if you’d like more good data. My efficiency is comparable to all of my former rigs so far.


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post #8 of 24 (permalink) Old 01-18-2020, 12:36 AM Thread Starter
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Well I'm only getting around 13-14 mpg with a 3.5 ecoboost if I can trust the dash indicator. Is it possible to get closer to 20?
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post #9 of 24 (permalink) Old 01-18-2020, 12:37 AM
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Quote:
Originally Posted by EatDirt View Post
Well I'm only getting around 13-14 mpg with a 3.5 ecoboost if I can trust the dash indicator. Is it possible to get closer to 20?
Yes. Unloaded I’ve hit near 20 a couple times.

Expect mid to high teen averages for normal use.

That said, I got the same with my 5.0 F-150 as I’m getting with my diesel (any of my 6 Cummins for that matter). If fuel economy is your only concern, maybe an ecodiesel 1500 is a better option.

However, if you need the increased capability, I think you’ll be happy with the 6.7.


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post #10 of 24 (permalink) Old 01-18-2020, 12:48 AM
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Quote:
Originally Posted by dillonjm View Post
There isnít any evidence yet that the HO or SO get better or worse mileage. If in compatible trim. There is a thread running around on here that calls the SO the ďefficiency motor.Ē I canít roll my eyes hard enough. Made up crap someone feels better about.

See my signature fuelly stats if youíd like more good data. My efficiency is comparable to all of my former rigs so far.
I'm pleased to hear that from someone that's more in tune with the gen4 trucks.

I have an HO being built soon and will have to put my A-Car/fuelly app to better use than I have been in the past.

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post #11 of 24 (permalink) Old 01-18-2020, 12:55 AM
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Originally Posted by brutal View Post
I'm pleased to hear that from someone that's more in tune with the gen4 trucks.

I have an HO being built soon and will have to put my A-Car/fuelly app to better use than I have been in the past.
Youíll find a lot of outlandish claims on forums about fuel economy. Mid to upper teens with normal use is what can be expected. Towing around 10-11.

Itís been the same on every Cummins Iíve ever owned.
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post #12 of 24 (permalink) Old 01-18-2020, 01:18 AM
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Quote:
Originally Posted by dillonjm View Post
Youíll find a lot of outlandish claims on forums about fuel economy. Mid to upper teens with normal use is what can be expected. Towing around 10-11.

Itís been the same on every Cummins Iíve ever owned.
I'm getting 9-10 towing 16K now in Colorado running around 65-70MPH on the flats with the 5.9 and he struggles entirely too much on the big hills and heavy headwinds given the (limited) mods installed and the stock 48RE is starting to act up at 72K. Sometimes closer to 8 if we're really loaded up for a week going out. I was getting 11-12 pulling just under 14K before we upgraded the RV.

If I keep the tuner turned down and keep my foot out of it, 21-22 empty on the lie-o-meter. More like 16-17 running 75-80 MPH with 4.10's and just 285/85/17's.

Getting 10-11 towing 16K would not bother me at all with the move into bigger power numbers.

A friend going from a 94 12V to his 2008 6.7L had been crying the blues getting 12-13 but I think it's gotten better or been flashed better. He's still only getting 8-9 hauling his big 16K RV around.
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