2001 Dodge Ram 2500 Diesel

Does anyone know what the optimal speed is to obtain the best fuel eceonomy with the 2001 Dodge Ram 2500 (4x4) Diesel Cummins 5.9? I have had many discussions with people who tell me one speed and others who tell me
another. My truck has a 5 speed tranny. I am aware of the fact that diesels do not like higher RPMs....
Thoughts anyone?
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AMT Tech wrote:

The Cummins PowerSpec program says the ISB's best cruise engine speed (for mileage) is from 2100 to 2400 RPM for vehicles 10,000 GVW and under. I believe that's true if your loaded or towing heavy but I've found the best fuel mileage at 2000 RPM or below when empty.
PowerSpec Report:
1.Select a gearing combination that will result in an engine speed of between 2100-2400 rpm at the vehicle's intended cruise speed (mph). 2.For maximum fuel economy or for vehicles operating 65 mph or faster, select a gearing combination that will result in an engine speed of approximately 2150 rpm at 65 mph checkpoint. 3.Gearing combinations that produce an engine speed less than 1900 rpm at the vehicles intended cruise speed (mph) should be avoided. 4.Note: ISB is not intended for weight over 50,000 lbs.
Engine: ISB Application: Recreational Vehicle Gearing Recommendation Type: Line Haul Typical Gross Vehicle Weight (GVW): Under 10,000 lbs. Percent time operating off-road or on soft surfaces: < 10% Percent time spent operating on Interstate highways: 90 - 50% Intended Cruise Speed: 70 mph Gearing Desired: Fuel Economy
The PowerSpec program that calculates optimum gearing based on information supplied initially by the user. Any variation between this input data and the actual operation could affect the accuracy of the results, and make comparisons with actual operating experience questionable. PowerSpec does not have the capability of making distinctions in resistance forces and factors affecting energy requirements, such as; Air Resistance due to frontal area or aerodynamic drag coefficient. Rolling Resistance due to tire construction (bias, radial, low profile radial, etc.). Air resistance increases due to winds and rain or snow. Rolling Resistance increases due to cold and rain or snow, or due to different pavement types and condition. Drivetrain and accessory loss increases due to cold weather. Increased fuel consumption due to use of blended fuels and long periods of idling in cold weather. Cummins is in no way liable for hardware selections made by the users. Specifications should be reviewed with the vehicle manufacturer dealer or with a Cummins distributor.
--
Ken



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In response to Nosey 's post. I thought everyone should know:

good info Ken and i'd have to agree with your observation. with the 05 6 speed anything below 65 mph will get me low 20's mpg as long as its not all city driving. that puts the tach right about 2,000 ~ 1900 or that neighbor hood.
--
Chris

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wrote:

Simply put depend on load on engine, any engine be it gas or diesel preoduces the most amout of work for fuel consumed when it is operating at or near its torque peak. This peak is where engine reaches its peak VI (volumetric efficency) and is its most efficent under load. The varible here is the amount of load because you do not want to load it to point of lugging and in which case a higher RPM with a reduced throttle setting will produce better MPG. Even still you want to keep RPM below 2300 IF max MPG is your goal. That engine does its brest work at that RPM an below for amount of fuel consumed. Sure it can rev a bit higher but efficency goes out the window as RPM climbs as big cylinder bore long stroke diesel engines (number of cyclinders vs total displacemen) do best at lower RPMs. ----------------- TheSnoMan.com
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A fair assumption.

That would be "VE", not VI, and the point of best VE isn't necessarily the torque peak.

Wrong. The amount of load has nothing to do with the VE of the engine.

True.
True.
True, but wind resistance of the vehicle plaays a bigger part assuming operation in top gear at highway speeds.
--
Max

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At one point, Cummins had recommended 1850-1950RPM for the ISB to operate most economically. I believe this is still true, based on personal observation in my 2000 Ram. The RPM mentioned in another post comes from RV usage, and so may not apply to your truck.
In my truck, a 2000 Ram, AT, 3.55 gears, my best fuel economy is observed at the above RPMs. I've found that with the truck empty and cruising at 70-75 MPH, my average over a long trip will be 19.5 MPG or so. Backing off and running at 60-65 MPH results in a better average. Depending on conditions, it can be as high as 22 MPG. at 60-65 MPH, my RPMs are 1900 or so. 70MPH results in RPMs of 2050 or so. On that same trip recently, I pulled an empty car trailer (1350lbs) down, and a loaded (3500lbs) car trailer back. My average was 18 MPG, and my speed was 60-65MPH.
However, I have to say that the biggest factor in fuel economy isn't the RPM at which you operate your engine, but the speed at which you go through the air. Wind resistance increases as a square of the increase in speed.
--
Max

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