I definately think there are things that can be done to the dodge cummins to significantly improve fuel economy. I bought my rig with the thot of fuel economy in mind (a diesel engine is more efficient than a gas engine. I actually rented a diesel 98 and a gas 98 before I purchased my rig and ran a 100 mile course with each and got 5mpg better fuel economy in the diesel so decided to purchase the diesel) I didn't care much about the power aspect but it seems that most people on this web site are more concerned about "bombing" their rigs. Especially with the cost of fuel going up I would love to see more and better info in this web site on increasing fuel economy. People often respond to my request for info on increasing fuel economy with a the idea that with the cummins pickup we can't significantly increase our economy because of the formula: weight vs speed equals MPG or some other such info, in other words our rigs are heavy, their like pushing a brick thru the air and there's really not much you can do to change the situation. I believe that if a Big rig pulling 70,000 lbs can get 6mpg at 60 mph (I actually went to a truck stop and talked to a number of big rig drivers and this was their average) then my 8,500 rig (includes my 2000 lb camper) should get significantly better than 14 under the same conditions. Also people with diesel pushing motor homes that probably weigh at least 30,000 lbs get 8 to 10. Wetspirit (previously in this thread) talked about improving economy by experimenting with Different turbo, different camshaft and different fuel timing. These are the kinds of things that I'd like to have info on that people have experminted with and have specific fuel economy results before and after results. For example, I was told by people on this forum and by the manufacturer that I could expect approximately a 10% increase in my fuel economy if I installed a True Torque Power Module from Diesel Dynamics so I purchased one. These are the results of 3 economy runs I made over a roundtrip course of 89.3 miles: 1) without the power module 17.82 mpg, 2) With power module set for timing only 17.82, 3) with power module set in #3 position (most agressive) 17.00. Needless to say I returned the module within 30 days and got a full refund. I tried to discuss my economy results with the representative and find out how they got 10% but he didn't seem interested, said most people were only concerned about the increase in power and it sure did increase my power but in my opinion my truck has plenty of power, stock and personally I'd sacrafice power for better fuel economy.

 

About the only thing you can do is to make sure you have a free flowing intake and exhaust and that you have enough boost for the amount of fuel you're burning (no smoke). Some use Water/methanol injection to increase power but I don't know if that has much effect on economy. You don't want to overboost because that will cost in terms of the engine working harder to compress a greater volume of air. In most cases however at cruise speeds you're at a low boost anyway and you're only injecting enough fuel to maintain equilibrium with the drag at the speed you're moving. If you increase speed much over 65 though you really suffer economy wise because drag increases faster at higher speeds especially with the 1st gens brick shaped body style. Otherwise, the usual suspects work to make sure you're getting the most miles per gallon of fuel. Proper tire pressure, reduce drag by streamlining your truck/trailer etc....

Miracle fuel additives just don't work. The factors you have to play with are engine efficiency and drag. That's it!

Edwin

 

I agree with you that it seems logical enough that if a big rig pulling 80K can get 6mpg, then a Dodge Cummins should be able to get a lot better than 14mpg.

Even at a basic level, it would seem that 1/4 the weight would give you 4 tiems more mpg-- or 24mpg.

This is without even accounting for the super heavy tires (and rolling resistance) and the worse aerodynamics of a big rig.

So it would SEEM that when you add it all up, something doesn't add up!

So what are the "non-linearities" that keep the mpg of the Dodge Cummins lower than it should be? You've no doubt read a lot on this already, so I'll spare you the regurgitation.

I'd agree that you should expect better mpg from a 4x2 truck than you are getting.

Heck, I have a 4x4, and I can get 20mpg hwy on a consistent basis-- and this is with the added drag, worse aerodynamics, and extra weight of a 4x4.

I'd expect 22mpg from a 4x2, and not be happy with less.



My first recommendation would be transmission improvement. I suspect a good portion of your fuel may be going into warming the trans fluid. A quality torque converter and valve body would probably help a lot.

What tires are you running? You need to fill in your signature with more specifics: 2500/3500, long/short bed, etc.


Finally, flat beds are really bad for aerodynamics. The faster you drive, the worse it gets.


Justin

 

I seccond the T/C VB upgrades, intake & exhaust... Maybe a Smarty on fuel saver?

Tall skinny tires aired to max pressure would also help, maybe 235/85's And synthetic driveline fluids should help as well. The flat bed is certianly not helping you.

Part of the problem is that most of us on here are more intersted in HP and torque than MPG.

ON EDIT: Lugging the engine will also hurt your MPG. And swapping to 3.08 rear end gears would maake a nice jump in your milage on the highway.

 

johnr9q
I've been looking for the same thing you have for a long time also. Injectors, timing, tires, and speed. Spray pattern of the injectors, atomizeing the fuel. Most claim improvements in mileage with some timing advance? Narrow tires inflated to max, and keep your speed 60mph or less.
I'f you want to go beyond that try adding a hydrogen unit or use waste oil to save money.
I've only had 7 of these trucks. None of them has averaged 20mpg on the hwy. Rare exception yes. 18mpg is the rule for highway. I tried the edge juice no difference, better intake filter, opened up the exhaust still no gains. Hydrogen is where I'm at now look at the alternitve fuels forum.

 

I'm with you guys. I feel that there is room for improvement on these trucks. I'm thinking camshaft and Torque converter upgrade would help significantly, but the cost of the two would take a while to recoup with the mileage gains. Although it would probably run and drive much better. The things we do

 

Hello- -

I have experimented with different setups and here is what I have found to help MPG.
First: Free flowing exhaust. The faster the exhaust gets out of the tailpipe the better. Exit your exhaust down and infront of the rear weel. 4" is plenty.
Second: TRUEFLOW Intake systems have been the best for MPG for myself. Remove Silencer Ring and Install a Turbo Fin (HoneyCombed piece of aluminum that actually speeds the air going into the turbo making it more efficent at the same boost levels. I have actually seen lower boost numbers pulling the same load up the same hill and keeping the same speed that I did while stock.
Third: Full synthetics in diff's and tranny's! Royal Purple oils/Amsoil- - - -Lower operating temperatures= longer life and better lubricity.
Fourth: TQ Converters/Lower weight flyweels- - less rotating mass! Better efficency than stock. Not as much slip!!
Fifth: Slower constant speeds, always under 70mph- - -68mph seems to be the magical number for all of my Diesels.
Sixth: Roll into the throttle while accelerating, keeping boost linear with no spiking.
Seventh: Tire Pressure 60-65psi
Eighth: Trailers= Higher tire pressures and make the load as aerodynamic as possible. Keep the trailers loaded so that the weight is distributed over the trailers axles and make sure that the trailer is at proper (Level Riding) height. Keep the nose of the truck stock height or lower if at all possible.
Ninth: Hard tonneau covers, or keep the tailgate up. Its been proven time and time again that the tailgate up creates less drag than the tailgate down.
Tenth: Smarty: Probably the best on the market for improved fuel consumption. Better Injectors that atomize fuel better.

Good Luck!!

 

It would be interesting to run a Cummins without the turbo and check the mileage. Max HP might only be around a hundred or so and it would have to be run easy enough to not smoke. But it might show that the newer (3rd gens) are using some power to make boost that is not needed at reasonable speeds. How much exhaust manifold pressure is there at, say, 10 PSI boost? The 1st gens, or the 12 valve second gens get better mileage and I'm wondering if the turbo is at fault on the later ones by making boost earlier than is needed to help keep the exhaust cleaner. It seems like my old '93 didn't get to positive boost till about 60 MPH if driven easily on level ground. How about one of the new variable turbos that we could set to "economy" for just cruising down the road. Also I've been wondering about the cams. Do they have more overlap than the earlier ones to dilute the charge for emissions? Is that how they got away with no EGR on the later 3rd gens and in the process lowered the mileage? I know the third injection cycle has an affect too. I'm seeing these new cams for the Cummins that can increase the mileage by 1 or 2 MPG. Do they really?
I don't expect to see any dramatic gains, because we're talking about a power plant that is only about 40% efficient at best. The piston engine in it's current form, is just incapable of truly great mileage or mileage closer to the potential in the fuel. And I like how heavy duty and capable my truck is, so I want better mileage without making it lighter or smaller or with smaller tires. Not too much to ask.
The over the road trucks, in spite of being very heavy and having a lot of wind resistance, can be geared to match the engine to the highway speed exactly, they average a little slower speed than passenger cars, and they make fewer stops per mile. They also have engines that have few cylinders with very large displacement. It seems like large displacement cylinders always do better (for a given horsepower engine). It may be because displacement increases faster than bore size (surface area of the piston is an exponential function) so less internal friction on a big bore engine, or that there are higher temperatures in the combustion chamber of big bore engines since the heat path to the cool cylinder wall is farther.
And timing seems to be a factor. Too bad we can't have a **** to adjust it with and a true gallons per hour meter that would actually read the fuel used instead of the time the injectors are energized.
In the end it seems like just slowing down is the most sure and effective way to get better mileage. But I don't want to slow down!

John

 

Since mileage seems to drop above 65 mph, and assuming it's due to drag, it seems that there are potential gains with streamlining. The fast 1/2 Dodge would be worth looking at for starters as they probably needed to address some of thse issues. Unfortunately a lot of improvements look dorky, like wheel covers, sloped canopies, air dams up front etc., but it's worth looking into.

Most of our trucks do have synthetics in the axles and manual trannies, at least synthetic blends in the autos, so there may not be as much to gain there.

Tires and tire pressure are obvious candidates, but most here seem to afflicted with what I've come to call 'corn', which is the complement to 'rice' used to describe the goofy mods on Honda Civics and whatnot.

 

The 10 points that Boostjunkie1 suggests may all be good but a scientific approach to determine the benefits of each one is the key. You need to determine the hand calc MPG before and after the mod. It takes time and money to really test properly. You need a course that is at least 100 miles and be a round trip course and one that you run at a time of the day where traffic will not slow you down. (the course I run is flat but ideally two or more courses would be used, one that is flat and one that has grades) Also best to run the entire course a number of times at various speeds, say 55, 65 and 75. You need to fill up at the same station at the start and finish of the course and at the same pump. You need to insure that you fill the truck tank to the same level each time. You need to run the before and after course as close together in time as possible and insure that the same conditions exist (wind, temp etc) The information I provided in a previous thread on the True Torque Power Module was obtained using the above guidelines. As I said, it is not easy to really check out a mod but anecdotal info info is not adequate.

 

I agree, and I always fill up at the same pump and fill to the top of the filler neck. Takes a while but I know that this helps in the accuracy. I drive 95% all Highway to and from work and after performing these mods to my 03 my HAND Calculated mileage increased from an average of 17.9 to 19.6mpg. Unloaded!! But I also noticed that there was a great improvement in the way the truck pulled even at lower boost levels.
My 01 was probably the best truck that I will have ever owned. I kick myself in the rear every time that I fill the truck up. I averaged 21mpg at 68mph. 6spd 3.55gears with the cruise set always. Same speed for the SO 03, auto, 4.10gears. The HO 01 pulled so much better and felt more like a truck. AHHHHHH those were the days.
Both trucks had all of the mods installed at one time, so no real test per mod.

 

Each engine seems to have a sweet spot for a balance of power and mileage. I have a 2003 SO with a stick, and friends with the 2003 HO with autos say they get about the same mileage, which is 16 to 18 mpg in town, 19 to 20 mpg on the highway. I think that they're geared a tad taller with the auto, as well have the 3.73 axles. The spread of 235 hp vs 305 hp and 460 lbs/ft of torque vs 555 suggests that the sweet spot is around there somewhere, as there are more complaints about mileage with the later model, higher output engines.

I've hit 20 mpg with about a half payload, so moderate amounts of weight don't seem to affect the trucks that much. Still, it'd be interesting to see what they'd do stripped down, like with an empty short bed regular cab, no spare, half a tank of fuel, etc.

 

Weight becomes more and more of an issue if you drive in stop and go traffic. Or if you drive to different altitudes. Generally, in the city you coast to a stop and brake but you have to accelerate that weight back up to speed with fuel. So over and over you're using fuel to accelerate but not getting anything back while stopping. Another example is driving up to the mountains. I get about 12 MPG towing my trailer up, and over 20 coming back empty. The weight is the variable. On a steady cruise, on level ground, weight should not matter too much. The biggest factor, and the one that requires no purchase of hardware, or redesigning the engine, is speed. It's speed, that's the biggy. If we were willing to slow down about 10-15 MPH there would be a big improvement with no initial investment.

The later model engines do seem to get worse mileage but I don't think it's because they have more power, it's because they have more tuning for emissions. The big mileage drop seems to have come with the 04.5-06 models. Of course, if you are using that extra power for fast starts at signals then the mileage will be worse just because you are using more power and thus, more fuel.

The automatics are geared slightly higher than the six speeds but the autos are hydraulic trannys and are less efficient because they are generating heat and maintaining hydraulic pressure. And they still have an overdrive that robs power, instead of a straight through design. The whole idea of "overdrive" is, in my mind, a marketing buzz word that people are fixated on. The most efficient tranny is straight through in high gear, and the axle ratio should be correct to provide the most efficient gearing in that straight through gear.

John

 

I too feel that overdrive is not the most efficient way to get the power to the ground. Our trucks should be geared higher and a better choice of internal transmission gears selected by the factory. Whenever you put power through more gears you are going to loose efficiency.

This is why I don't feel that there are big gains to be had using units like U.S. gear or Gear Vendor overdrive units.

 

Sled,

No kidding. An extra tranny or gear splitter will allow you to split the gears for extreme heavy loads, but it brings inefficiency. Before it could help at all it has to more than makeup for another problem that should be corrected some other way. There is a lot to be said for keeping it simple. Why spend thousands of dollars to add a part that adds inefficiency to correct another inefficiency?

John