First of all I want to say that I am a newbie to Diesel trucks, never ever owned one but have friends that own them. Mostly Dodges. I did alot of research before I bought my used 2007 Dodge 2500 4x4 Diesel 5.9 cummins with 6-speed manual. Alot of people that I know own these trucks and have bragged about the mileage that they get. I have ridden in these trucks and was very impressed with everything about them including the power.
To tell you a bit more about my truck before I tell you my woes. The truck is bone stock, no mods anywhere.

Being a newbie to Diesel trucks I have a few questions and probably alot of these have been answered in other threads but I wanted to post them to get some expert advice.

First of all I have questions about the RPM range that my truck should be running with the 6-speed manual, 3.73 gear ratio and 4wd. At 75 mph it runs at 2300 RPM, 70 MPH about 2050 RPM and 65 MPH about 2000 RPM.
Is this normal or is something wrong? It's seems to be high for a 6-speed manual truck.

Next is the MPG, when I bought the truck in August it had 87,000 miles now has almost 94,000 miles. The first tank full of gas I was able to get 18 MPG running 70 MPH and 17.5 MPG at 75 MPH both times running empty all calculated by hand not based on the lio-meter.
I was expecting way more than this based on the information that I had researched. That is why I bought a diesel truck because I could get better MPG out of a 3/4 ton diesel truck than I could from a GMC Yukon.
I was expecting around 19 - 20 MPG instead of 17.5.
Since this time running empty I was averaging 17.5 MPG running empty. While pulling a two place snowmobile/atv trailer (this trailer is heavy built but no 10,000 lbs) I was able to 12.5 MPG at 70 MPH.
This sucks in my book. The MPG should have never dropped when pulling this trailer in my book.

Also I have changed the fuel filter twice since I purchased it in September thinking that this might be part of the problem and they have not made any difference.

I took the truck to a Dodge dealer to have them check it out for any problems and they told me that there was an ECM update available for the truck that would help fix the mileage and other things and since then the weather has turned off cold and my mileage has went to 12 - 13 MPG loaded or empty.

At what RPM should the turbo kick in? And shouldn't I be able to hear it spool up?

Does anyone have any suggestions for what to check for to improve my MPG? I am very disappointed in this part of my truck because the GMC Yukon 1/2 ton 4x4 would get better MPG loaded or empty than this diesel.

I know lots of questions, I would like some suggestions on what to look for or what might be going on with my truck to get such poor mileage and poor performance.

Thanks

 

At 75 you are driving a brick slow down alittle mileage will go up, as for the 12.5 how big is your trailer.

 

Welcome to the forum.. keep in in mind winter blend will not give you as good mileage as summer.. Top off the tires and like Purplezr2 says slow down a bit(set the cruise control).. I get 20+ at 70 on the hwy with the 05.. Try some fuel additives as well, they will improve your millage and keep things lubricated..

 

i loose 3mpg during the winter because of the winter blend fuel. put a larger tire on it to reduce rpm's and that will help.

 

your rpm are like that because of the G56 tranny as opposed to the nv5600

 

Dude, what they all said....+1

If I push my dually (heavier than your rig) up over 60-65 my mileage drops by 8-10 mpg's!
If i hit the cruise control and keep it in the 1600-1800 rpm range I can squeeze about 24-26 mpg out it on the freeway running empty.
If I hook up to our 40' triple axle enclosed 5th wheel car trailer then it drops like a rock to around 15-17 mpg on the same freeway.
Keep in mind I have almost 190K miles! The moremiles you get the better the mileage.
Check out the thread son here on MPG's and you could spend all weekend reading up on the subject.
Add in the benefit of synthetics in everything from engine to rear end and you have the reason for the great mileage claims.
If you drive that thing like a gasser, expect gasser mileage (which you apparently already know) Being a 4 x 4 will kill some as opposed to a 2 wd rig, and running those big swamper mudders will also contribute to the pisspoor mileage thing.
I keep my tires up at 80 psi, use full synthetic everywhere I can, even wheel bearings and driveline u-joints and have virtually no backpressure on my exhaust (4" from turbo back to the 6" stacks) so I let this baby breath all it wants.
It's a very interesting thing, this fuel mileage stuff. I can be on the road to a great 700 mile run on a tank full and then get stuck in traffic, sit at a stop light or two and literally watch the mileage drop like a rock. Yes, hand calculating is the best, but for on the fly data the lio-meter is close. It shows you which way the mileage is going...

 

I had ran a 96 F250 Ford with the 7.5 (460) for 12 years. I bought it new and ordered the 4:10 axle with the 4 speed automatic. This truck used lots of fuel. It delivered 10 mpg most of the time towing and non towing. I have seen 9 mpg while towing a 5800lb low profile 5th wheel. However on two occasions I hand calculated 14 non towing! On these two fill ups I had topped the tank, drove 90 miles on the Interstate at 50 mph and then got off and topped the tank. There was absolutely no city driving. I could not drive faster because of early morning fog. It made me realize how much better my mileage was at 50 vs 70/75.

When I traded it for my 05 Ram Cummins I immediately started hand calculating mpg. If you keep your RPM below 2000 it should deliver 19 non towing highway and possibly more. I have logged 22mpg highway running 60 or less non towing.

Bottom line is this, speed has everything to do with mileage. Stop and go has a tremendous effect on it also. You will find this to be true on gas and diesel engines of all makes and classes of vehicles. Your best mileage is obtained at a speed where it runs in 4th gear without lugging the engine. Years ago the highway mpg figures on new vehicles was calculated at 48mph. I'm not sure how it is done today because they use a more realistic approach. 48 mph is not realisitic driving.

 

You will also get worse fuel economy in the winter. The blended fuel, the air is more dense, the oil in the differentials is thicker, you are also taking btu's from the combustion process to keep the engine warm in cold temps. That takes an amazing amount of fuel if the engine is running cool/cold. Do you have a winter front? Blocking that icy blast from hitting that radiator can make a huge difference.

 

Thanks for all of the replies. I know that I need to drive the diesels a bit different than gassers but I have tried everything to get my MPG to improve. So what you are all telling me is that I need to drive this truck like a grandma (haha) to get the best mileage? Who wants to drive like that. I know from talking with my friends that I will lose MPG in the winter while running winter blend and that makes sense to me.

I am not expecting the world from this ton of bricks but I was expecting more from the MPG but I guess that I need to change my driving habits even more. When I was pulling the same trailer (I will post pictures of my setup later) at 75 MPH I was able to get 10 MPG from a GMC Yukon 4x4 with a 350, I assumed that this diesel would be able to get better than that. I know I shouldn't assume.


What about the turbo? In my original post I had asked some questions about the turbo. At what RPM should the turbo kick in? And shouldn't I be able to hear it spool up?

 

You should sell the truck. Sounds like you're unhappy and it's not living up to your expectations. Put that young 5.9 back into the market rotation so a more appreciative owner can purchase it.

Honestly, it just sounds like you fantasized a diesel right out of the reality and your friends really worked you up.


If you want to hear the turbo spool up pull out the silencer ring. Otherwise turn off your AC and radio and listen for the whine after you press the go pedal. It's there.

Here's a FAQ read: http://dodgeram.org/tech/dsl/FAQ/turbo_faq.htm


No one wants to drive like a grandma all the time. Here's a secret, no one does. You just gotta do it the majority of the time. Usually every third or fourth tank is lower mpg than the others because I go on a streak of not driving like grandma

 

I have to agree with everyone else but at the same time im going to tell you your lucky, my uncle's 04 hooked to a 16' stocktrailer is a thirsty little pig for a 5.9, if he keeps his foot out of it he might break double digit fuel economy haha.

Mostly i agree with Shorts, you imagined it would be far superior to what the reality of a diesel normally is

 

As much as we want a 8,000lbs, stump pulling, 4x4, lifted beast on 44 inch tires going 90mph pulling 9 tons and getting 42.56mpg its not a reality. A buddy of mine has a 2001 Ford F250 4x4 with a 5.4 gas engine and he gets 11-12mpg at 75mph to my 16-17, and my truck weighs more. Your truck is fine. Your expectations are just a tad too high my friend. If this truck makes you unhappy, no need paying for it. Just sell it and get a gasser and end all your frusterations. :-)

 

Can't say too much about the Ford performance......but can say that 19-22 for a pre-2003 diesel is pretty good. But despite the power that you get from the diesel, they are not hotrods (they will run like one, but you'll pay the fuel price). Drive like a Grandma? Yup, if you're looking for optimum fuel mileage.

 

My first 700 miles in my truck, a 2006 5.9 got 17.5 MPG running just under 2000RPM most of the day with an occasional burst of speed to get around some freeway traffic etc. I was real pleased with the 17.5 for a 3/4 ton truck. My Toyota extended cab V6 1999 gets 20-22 if I go 62 MPH and if I am pulling a 18 ft Lowe Roughneck with a 75Hp Merc decked out with camping and fishing or hunting gear I'll get 14-15 with a engine that is working like a hog in a breeding pen.

I've driven Isuzu, Ford and Cummins commercial trucks and you need to watch the RPMs to get good economy. Find the 'zone' for your truck and you'll be happy.

 

Something is wrong if you are getting mileage the low when towing, I pretty sure guys that pull GNs get that kinda mileage towing. Also diesel worksd better if you tow heavy, Example, my bosses yukon pulling 5500lbs for 1/2 the miles and maybe 1800 for the other 1/2, running hwy speeds (55-70) got around 8. My truck making the same trip and same load I got around 16.5. My truck is older and get better mileage since I don't have extra injection event