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Old 03-24-2014, 10:32 PM   #1
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Unhappy Diesel fuel mileage (MPG) seems low

I recently purchased a RAM 3500 DRW with a 3.73 rear end. I am only getting about 14-15 MPG at 65 W/O any load and about 8 MPG towing a Montana fifth wheel on level road. Is this all I should expect. My old 5.9 2007 got about 21 unloaded and 11 MPG pulling the same fifth wheel.

What type of mileage are others getting and what do they have is data I would like to get.

Is there any way to improve the mileage besides trading truck?
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Old 03-24-2014, 10:48 PM   #2
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Slow down about 3 mph. Keeps rpm under 2000. That will improve fuel milage.
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Old 03-24-2014, 11:09 PM   #3
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I get 15-16 solo with a 2009 3500 DRW 4WD, and between 9.5 and 10.5 towing a 13,000 pound fiver. I figure my mileage solo is down about 15-20% from my 1997 5.9 2WD 2500, and about 10% towing at 62mph.
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Old 03-24-2014, 11:23 PM   #4
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How many miles on it? My '13 3500 dually with 4:10's is slowly getting better and I am now getting 17 mpg at 65 mph.
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Old 03-25-2014, 08:36 AM   #5
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Quote:
Originally Posted by crewstx View Post
I recently purchased a RAM 3500 DRW with a 3.73 rear end. I am only getting about 14-15 MPG at 65 W/O any load and about 8 MPG towing a Montana fifth wheel on level road. Is this all I should expect. My old 5.9 2007 got about 21 unloaded and 11 MPG pulling the same fifth wheel.

What type of mileage are others getting and what do they have is data I would like to get.

Is there any way to improve the mileage besides trading truck?


What year truck? This will make a very big difference on fuel mileage. The older 2007.5 to 2012 trucks with the 6.7L engine used a different emission control strategy than the 2013.5 and up trucks. The poorer fuel mileage with the older engines is due to the fifth injection and the injection of diesel fuel in the exhaust cycle when regeneration is required, and excessive EGR taking place at idle.

Now with the SCR emission strategy diesel fuel is now longer required to clean the DPF and there is less EGR taking place thus the fuel mileage has improved tremendously over the older trucks. Along with other fuel management changes to the engine.

The only way to really improve fuel mileage other than deleting the emission system which is illegal is too slow down and drive under 60 MPH. This is where I get my best fuel mileage on my truck which is between 55 and 60 MPH, I get about 11 MPG.

Remember you have a very large SAIL behind you trying to slow you down and you are pulling this sail down the road.

Jim W.
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Old 03-25-2014, 09:07 AM   #6
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This is all interesting information. I just purchased a '12 Ram DRW to handle the new Dutchmen Toy hauler we have on order. With this information, I almost wish I had gone ahead and went with a new '14 Ram.
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Old 03-25-2014, 09:15 AM   #7
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I had a 2011 ram with Cummins diesel motor. What I noticed from all the older Cummins diesels I had was that towing mileage was very similar to older ones. The empty mileage was where it suffered over the older engines. I suspect that the engine working harder towing was producing enough heat that it did not have to add extra fuel for DPF. When empty it had to add extra fuel there for lower MPG.
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Old 03-25-2014, 09:17 AM   #8
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DEF rams should give better fuel economy and the engines run cooler because the exhaust is more free flowing with a more neutral tuning.

I personally wouldn't buy a DPF only diesel truck. They are tuned to run hotter(produces less NOx but more Particulate Soot matter), which also reduces fuel economy on top of the regen burn cycles.
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Old 03-25-2014, 10:10 AM   #9
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Just remember folks, the EPA is run by rocket scientists who know exactly what is best for us.
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Old 03-25-2014, 03:12 PM   #10
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Just remember folks, the EPA is run by rocket scientists who know exactly what is best for us.
EXACTLY. Nuff said.

Chad
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Old 03-25-2014, 04:25 PM   #11
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Now with the SCR emission strategy diesel fuel is now longer required to clean the DPF and there is less EGR taking place thus the fuel mileage has improved tremendously over the older trucks. Along with other fuel management changes to the engine.


Jim W.
Im not going to say im 100% sure but 95% sure that any DPF equipped truck will go into a regeneration by adding raw fuel into the exhaust upstream of the DPF. DEF is used for a different emissions control. The DPF is still used to collect soot and regeneration by adding raw diesel fuel to raise temps over 1000F is needed to cook the soot in the filter. A quick google search and it appears that the Cummins is not exempt from cleaning out a DPF. However the newer diesels out of the big three do seem to have less regen than earlier ones due to the DEF fluid and the aid of passive regeneration.
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Old 03-25-2014, 04:35 PM   #12
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I don't think that the fuel required for occasional DPF regeneration is enough to significantly impact overall mileage, if anything it would more likely be the exhaust restriction caused by the DPF. Or maybe it's the EGR. Or maybe it's tuning to support use of DEF. IOW, I don't think you can single out a single system as being responsible for MPG reduction, modern diesel emissions controls are very complicated but that is one of the prices paid for clean air. If you don't like DPF or EGR or DEF then by all means design a system that works better... you'll make millions.
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Old 03-25-2014, 04:38 PM   #13
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Did , Dodge / Cummins repairs at a dealership from 93>07. Every time the rated HP was increased the fuel mileage went down.
That being said, these engines have a LONG break in period, don't expect your best mileage till 15k + miles, vary the RPM, often on a new motor and check your owners manual for cruise control use during the break in, some years they said not to use cruise for the first 10>12K miles.
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Old 03-25-2014, 05:21 PM   #14
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I have a 12 CTD SRW and get decent MPG. 10.5-11.9 towing and 5'er. I get 17-18 on the freeway running 65-70mph. I see a drop in mpg when the regen starts. I can tell when it's regening cause the mpgs drop. With that being said it's not in regen long enough to really affect mpgs. It will but on a long trip it's not all that noticeable. The DEF equipped trucks should do better than mine.
To the OP I would take it in and see if it needs a reflash or something. You mpgs are way to low.
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