How to get better fuel economy w/your diesel

trendomtrendom Member Posts: 2
After talking to hundreds of folks across the country I found that the average diesel owner gets 15-16 mpg.

Also what I have found is the "posted speed limit" has everything to do with mpg.

If someone lives where they hardly drive over 60-65 mph unloaded they will most likely brag that they typically get 19-20 mpg.

Someone who drives 75-80 mph will most likely be getting 14-15.

I have personally taken and compared side by side a "broke-in" 05 Cummins and a 05 Power Stroke.

What I found was at if I maintained a speed of 65 mph I averaged 18 mpg. Once I increased my speed to 75 mpg I averaged 14 mpg. SAME TRUCK... 4 MPG DIFFERENCE.

The Cummins actually dropped less mpg than the Power Stroke with the increased speed and I contribute that to the fact that the Cummins hits it torque band faster at lower rpms.


(I did however talk to a guy the other day that installed a performance module called the Workhorse and says it increased his 05 PS MPG from 15 to 20. He also said towing a boat he still got 17mpg. He said he bought it at


  • madeinamericamadeinamerica Member Posts: 1

    I'm new to the group, and have a few questions for everyone. Currently I own a quad cab 2500 4x4 diesel Ram and get an average of 14.2MPG with a highway speed of 72MPH. Can anyone tell me from experience how much better fuel milage is switching to a synthetic motor oil? Also can anyone tell me how much better the fuel milage is when using a cold air intake on hte Cummins engine? These are two options I am considering to try to get my MPG to around 18 without easing my foot on the gas pedal.

  • KCRamKCRam Member Posts: 3,516
    The Cummins is more affected by gearing than anything like motor oil viscosity. My 96 Ram 3500 4x4 with stock tires and 3.54 axles nailed 24.3 mpg over 270 miles at an almost steady speed of 57 mph. My 05 3500 4x4 with 3.73s and stock tires has no trouble hitting 20 mpg at 55 mph. However, I will lose about 1.5 mpg for every 10 mph over that. If you have the 4.10 axles, it will be even worse.

    kcram - Pickups Host
  • tex10tex10 Member Posts: 27
    some guy was telling me that desiels do better on a bigger tire. but he said after 35" inch tale tires every thing gos to hell gas, axles, transmission.
  • cornfedcornfed Member Posts: 2
    I have researched the aftermarket gear vendor overdrive/underdrive that basically gives the cummins diesel 6 spd transmission 11 gears.

    I did this after test driving a 2500 Dodge cummins 6spd today and found it very disheartening to be running at 2500 rpm at 75 mph. The Rep at Dave Smith Motors i Idaho told me about the option and my internet research seems to be pretty positive, makes sense if you got 11 gears like a semit truck your engine runs more efficient and thus better mileage. the add on is 2900.00 per the dealer. Any thoughts? anybody running one presently? I do alot of highway driving, rarely tow and want the engine to be relaxed going downt he interstate.
  • mullins87mullins87 Member Posts: 959
    Gearing is all important with a diesel engine, that's why big trucks have multiple gears. The ones I've had any experience with had 9 speed Eatons, shift 1-5 in low range, then hit high range and go back to 2nd to get 6th gear, then on up to 9th. Unless you can switch the range on that overdrive unit while underway, you'll still only have 6 gears. I admit, I haven't looked at the Gear Vendor unit in a fairly long time, maybe they changed that.

    Do you have a 4.10/4.11 gear ratio? 2,500 rpm sounds about right for 75 mph with that ratio. I had an F-350 with 3.73's in it and it ran around 2,100 rpms at 75 mph. I'm afraid that if you go with an overdrive unit, your highway performance will suffer. Turbocharbed diesels need some rpms to get the turbo spinning fast enough to create boost, which in turn builds HP. Find out the overdrive ratio, is it a 15%, 20%, etc... Reduce your engine rpms by that percentage to figure out what your engine speed will be at a given speed in 6th gear. Then get out on the road and try driving in 6th gear with the engine near that rpm. You'll probably want to do this on a not so busy road since you'll probably be driving slowly. Then roll into the throttle. If the truck has plenty of "get-up-and-go" to it, then the overdrive may be an option. I'm betting the engine won't be spinning fast enough. I know how my F-350 drove at 1,600 rpm in 6th gear, even with a chip.

    Another option is to just regear your axle. I think that would be considerably cheaper.
  • sirmavericksirmaverick Member Posts: 2
    Has anyone installed the Bosch Upgrade injectors? I have a 12 valve cummins and was wondering if they noticed a difference in their mph or torque and horsepower?

    here's a reference link: the exact ones I bought:
    auction from the guy I bought from
  • ezshift5ezshift5 Member Posts: 858

    ..I couldn't agree more.

    ..doing 55 mph (absorbing big time nasty looks from many citizens), my diesel will turn in that same figure in mpg. Increase to average citizen speed and fuel efficiency heads for the cellar. I plan ahead, drive 55 and try to avoid eye contact.......

    all the best, ez
  • KCRamKCRam Member Posts: 3,516
    Same here... at 55mph, I get a solid 20 mpg in my 05 Ram 3500 Quad Cab 4x4 dually (Cummins, automatic, 3.73 axles). At 65, that drops to about 18.

    kcram - Pickups Host
  • farmboy4farmboy4 Member Posts: 9
    I'm buying '98 2500 Laramie SLT diesel 4X4 with automatic transmission. I'm looking to get better mileage than my 2000 1500 gasser. Keeping track of how efficiently I'm driving is important. The truck I'm buying has an overhead console but doesn't give the average MPG. Does anyone know if this is just something wrong with this particular console, or if direction and temperature are all it every showed. If it's a model that only shows direction/temp or is just not working on the MPG function, does a replacement console have to be specific to a diesel? Also, if the existing console came only showing direction & temperature, would the wiring be in place for a console that will show MPG? Is everyone totally confused now by what the heck I'm talking about? If not, thanks for your help.
  • steedoflondonsteedoflondon Member Posts: 8
    Here's my mileage numbers on my 2004 Dodge Ram 2500 diesel quad-cab with a 4-speed automatic. We started the journey with approximately 9,500 miles on the clock. We averaged 19.49 MPG.

    Col1 Cumulative Miles Travelled
    Col2 Actual Miles Travelled
    Col3 Number of Gallons
    Col4 Miles/Gallon
    Col5 Price/Gallon
    Col6 Fill-up State
    Col7 Fill-up cost
    Col8 Comments

    Col1 Col2 Col3 Col4 Col5 Col6 Col7 Col8
    389.1 389.1 22.20 17.53 $3.16 CA $70.13 Mostly freeway at 80MPH
    640.9 251.8 14.00 17.99 $2.86 OR $40.01 Montain, Coast and freeway
    1003.2 362.3 17.07 21.23 $2.73 OR $46.59 Mostly freeway at 65MPH
    1352.2 349 17.69 19.73 $2.99 WA $53.04 Mostly freeway at 70MPH
    1702.8 350.6 16.97 20.66 $2.84 WA $48.18 Freeway, mountains, traffic
    2143.6 440.8 22.24 19.82 $2.79 OR $62.02 Mostly freeway at 70MPH
    Average MPG 19.49

    These numbers are based on a round-trip journey based on driving up I5 from CA into Vancouver BC, and then back into CA. This includes moutain passes in northern CA and southern Oregan, as well as driving from Vancouver BC into Whistler. Note that I haven't included the last fill-up here, since I haven't filled up the tank yet!

    Some points of interest... diesel is way much cheaper in OR & WA. In fact I think that us Californian's are getting ripped off. I'm not sure why diesel is so much more expensive in CA than the other states. Any ideas? Would be interested to hear what others are paying in their locale.

    The mileage numbers are based on using the tried and tested method of Miles travelled divided by number of gallons. I haven't checked the onboard computer... but I don't know if I would necessarily trust it.
  • farmboy4farmboy4 Member Posts: 9
    In reply to steedoflondon. I live just outside of Philadelphia. I haven't paid a lot of attention to the cost of diesel because I didn't have a diesel, but would occasionally notice that the cost of it was about 25 or 30 cents more per gallon than 87 octane. I'm in the process of buying a Dodge Ram 2500 diesel so have been paying more attention lately while I've been looking. At most stations that carry diesel the price is still higher than 87 octane, but several weeks ago I was at a station and diesel was 7 cents cheaper, $2.459 vs $2.529 for 87. Today I went by the same station and diesel was still $2.459 but 87 was $2.599, a 14 cent difference.
    Can anyone also recommend a good light truck tire that will help get good mileage? I'm never off road, don't tow anything, and don't usually have a very heavy load. I do, however, need something that will get me through wet roads, snow, and ice, without costing a fortune. I'm trying to save money, not just shift the spending from gas to tires.
  • steedoflondonsteedoflondon Member Posts: 8
    Just one point to add to my original posting. The onboard trip computer in the truck states that I got 18.7MPG during the trip. I'd actually expected it to be more optimistic than my calculations.

    During the trip I only noticed a couple of places that had diesel less than the middle or premium grade of gasoline. I didn't see a place that was cheaper than regular.

    in response to Farmboy4, have you considered taking a look at Biodiesel (e.g. and then seing if that is cheaper than #2 diesel in your area?
  • bruchkobruchko Member Posts: 3
  • bruchkobruchko Member Posts: 3
    I recently bought a 2000 F-250 Crew Cab Lariat SB with the 7.3 Powerstroke with 68,805 mi on it from a dealer. It's a 1 owner vehicle and is in great condition. When I test drove it the mpg readout said 17.1. I took it home for the weekend and it was down to 15 when I took it back on Monday. Since buying it 2 days later (2 weeks ago) it's now getting 13.3 mpg. The dealer has a good reputation though I've never bought from them before. The fuel filter and air filter have been changed, it runs fine and I'm not driving it hard at all. I've tried getting fuel from different places but no change. Any suggestions?
  • farmboy4farmboy4 Member Posts: 9
  • farmboy4farmboy4 Member Posts: 9
    I'll only speculate that the 17.1 readout was the average of what the previous driver had been getting on the way he was driving, maybe mostly highway miles, and what you're seeing reflects a different type of driving, maybe more stop and go.

    Also, if you go to the AAA website at, click on the Automotive tab. In the upper right side of the next window you'll find a spot to click on for fuel prices in your area. Here's a comparison of stations that sell diesel within 10 miles of me in Glenside, Pa.

    Brand Regular Mid Premium Diesel
    Hess 2.62 2.72 2.82 2.56
    Gulf 2.62 2.80
    Hess 2.62 2.82 2.60
    Sunoco 2.64 2.80
    Texaco 2.66 2.76 2.88 2.99
    BP 2.66 2.92
    Hess 2.68 2.74 2.60
    Sunoco 2.70 2.80 2.77
    Mobil 2.73 2.87
    Sunoco 2.76 2.84 2.85
    Sunoco 2.78 2.80
    Exxon 2.90
    Gulf 2.86

    You'll notice that Hess is the one that sells diesel cheaper than regular. Someone told me yesterday that Hess has their own refinerie so doesn't have to buy it from someone else.
  • bruchkobruchko Member Posts: 3
    True, I am doing more stop-and-go driving. I think the previous owner pulled a horse trailer or an RV. I only pull a pop-up camper or a fishing boat from time to time. This truck is in almost brand-new condition throughout. I had my mechanic give it a once-over and he thought it was a great deal. I paid 23K.

    A local diesel repair shop said my fuel jets are probably dirty though I would think a dealer would clean these out before selling the vehicle. I'll try that before looking into a performance chip. I don't need more horsepower, just better fuel economy. I'm looking into the "Workhorse" performance module as a possible solution if I need to. The dealer says it doesn't inject more fuel, just burns it more efficiently.

    Here in the Parker CO (just SE of Denver) diesel is between 2.56 and 2.69 depending on what part of town you're in.
  • rafitarafita Member Posts: 1
    I have a 94 Cummins, just bought it.... I power washed the motor last night and when I was about to turn it on..."water in fuel" light came on....I did leak the filter like the manual says.... but the light keeps coming on.. will this light go off after several driving cycles,,,Please help..

  • kerckhofkerckhof Member Posts: 6
    Diesel in Walla Walla Washington, SE corner of Washington, is 3.30/gallon. :cry:
  • viking6viking6 Member Posts: 3
    Ok i just wanted to know about the mph for my new truck. Truck is the 2002 F250 XLT CREW CAB SHORT BED 7.3L diesel, 4x2 Can someone tell me what kind of mileage i should get in the city/ highway. I am not planing on towing or hauling anything.
    Thank you :confuse:
  • cactus5cactus5 Member Posts: 22
    It's seems like it's been forever that I wanted a Dodge Ram 2500 quad cab and this tuesday 9/19 it happen got an 06 Big Horn 4x2 auto trans and limited slip. I'm 54 years old all I can say is WOW everything I hoped it would be. Avondale dodge fleet dept. ROCKS they drove it up from tucson for me and it even came full of fuel. Only the odometer LCD does not work. My girlfriends cousin steve wanted me to get a DuraMAX and her other cousin Victor has a powerstroke. But I think cummins is the best.
    I have been reading comments from all you guys for at least 8 years about your diesels. Well welcome me to the club. I'm ready for some advice. By the way I named her " Lucille" after lucille ball
  • cactus5cactus5 Member Posts: 22
    Silly me ,I took the word of a 20 something [ he drives a 05 Ram 1500] who said it was under the tach. When actually it's under the speedo. Yes my odometer does work.
  • cdb3cdb3 Member Posts: 1

    I will share with you what I have learned about mileage on the truck you mentioned. I have driven a 2001 F250 with the 7.3 P-stroke for 4 1/2 years.

    You cannot go by the mpg readout for the short term. It can be fun to play with and may be used as a guide but it is not accurate. Certainly don't trust it to accurately tell you how much further you can go without fueling! You can reset it by pushing both buttons at once while in the mileage mode. Did you know it measures temperature and distance to empty as well as mileage? Toggle to the different modes by pushing the button on the left side. It can also be set to measure in metric.

    The only way to get an accurate reading for your mileage is by carefully filling the fuel tank all the way to the top of the filler neck until fuel no longer runs down. Pumping diesel is not unlike pouring warm beer - lots of foam. Ford has never chosen to put a large filler hose on the pick-up tanks like I think Dodge does. Completely filling in warm weather will take about five minutes after the filler starts to automatically shut off.

    Anyway fill it up into the filler neck until fuel is w/i 1/2 inch of the cap and stays there. Drive until you have used up 3/4 or more of your fuel. Fill up the same way. All the way to the top, get past the foam! Use a calculator or pencil (God forbid!) and divide the gallons into the miles.

    Do this for every kind of trip for a year and you can see what your truck is really doing.

    These trucks do much better on the highway than in town. They will run like hell but if you want better mileage accelerate slowly, use cruise control and keep your speed down. Wind resistance at 70 mph is twice as much as at 55 mph (as per NPR last week.)

  • santa1santa1 Member Posts: 1
    Last January I bought a very nice used 01 F-250 7.3 Turbo prw stroke.It is a 4dr shortbed ( my wife and I,75 & 70,enjoy the comfort), I am a professional Santa Claus and we travel to SE Pa. every year to do Santa, my question is- can another fuel tank be installed in place of the spare tire? We have a 30 gal single tank and would like to have an aux. to take advantage of the (rare) times we find a good deal on Diesel fuel. I haven't been able to find any info on doing this here in South Central Texas. Does anyone have answers for the "Old Folks"? Thanks, Santa
  • yrbenderyrbender Member Posts: 25
    I purchased my F250 4X4 crew cab diesel in Feb. 05 at that time diesel was about .10 cheaper than regular gas. Today the price of diesel is 0.75 more per gallon than regular! Does any one know why diesel is more now and should this trend continue?
  • brookshdbrookshd Member Posts: 8
    My '02 7.3L consistently gets 15 to 18 mpg, loaded empty, combined gross vehicle weight of almost 30,000 lbs (over the rating, DO NOT try pulling that kind of weight without airbag suspension and equalizer hitch and bars). I can be pulling passes or running flatland. I have the superchip and K&N million mile air filter, otherwise bone stock motor. Keep your tire pressure up, it changes with temp and altitude. Top speed is 95 mph, not built for speed, built to PULL. Nothing really seems to vary my average or tank to tank mileage.
  • polsonpolson Member Posts: 1
    Here is what I have learned over the past 4 years or so with some experimentation.

    First off, let me say, my stock 2002 Ford 7.3 got about 15-18 mpg. I drive 140 miles round trip (all interstate) to work and back so I have had plenty of time to figure out what makes it tick.

    Gearing is everything. My truck runs 3.73 rear ends. To the engine I have added a K&N filter and air box. I also modified the front intake behind the grille for better airflow. The stock intake was about the size of a silver dollar and I took a dremel and opened it up. Also, a 4" exhaust made a big difference. The engine had more "snap" and it lets the turbo spool up noticibly quicker. I also have reflashed the computer with a power programmer. I left it at the 60 HP "performance economy" mode. I am not drag racing it and I was going more for mileage. I also reprogrammed the transmission for stouter shifts. As you all know, the stock transmission setting is a little mushy. Also, a set of decent quality gauges are an absolute must. Heres why: The lower you are able to run the boost, the better your fuel economy. I have experimented with different highway speeds and found that with the 3:73's 55-60 MPH equals 24MPG. The faster you go the more boost the turbo produces the lower the fuel economy. At 70 MPH the mileage drops off to around 20MPG. Now, if the gearing were a little taller say 3:08 it would stand to reason that the fuel economy would be better at highway speeds. Conversly, with 4:10's or lower expect the turbo to be building more boost at highway speeds and fuel mileage to suffer.

    Food for thought.
  • ezshift5ezshift5 Member Posts: 858

    ".....I have experimented with different highway speeds and found that with the 3:73's 55-60 MPH equals 24MPG. The faster you go the more boost the turbo produces the lower the fuel economy......"

    ..IMHO, that is impressive fuel efficiency for a 7.3l TD...
    well done!!

    (this from the left coast: 1.6l non-turbo trucklet.......

    seasons best, ez....

  • tjmax2tjmax2 Member Posts: 1
    Cactus 5
    I have a 05 Dodge 4*4 HO turbo diesel w/ 14k miles
    My first easy add on would be a K&N air filter
    worth every penny, aprox cost $60 and you can hear the diesel breath easier after instalation.
    After break in period I would highly reccomend full synthetic oil for the motor. The rear end should be synthetic already from the factory. Keeps it cooler and actualy reduces some noise!
    Hope this helps

  • boxmaker1boxmaker1 Member Posts: 1
  • roughneckroughneck Member Posts: 21
    In case you haven't found an auxiliary fuel tank yet. You can get some from Northern tools. I think they have about six to choose from. Once u get one u can run a fuel hose from the aux. tank through the filler neck to keep your main tank full. I've got a 91 gallon fuel tank toolbox combo and love it.
  • jyardjyard Member Posts: 1
    Has anybody experienced fuel problems like this with your 05 diesel? The dealership preformed afuel economy update to the truck and my trans serviced also .I dont know if any of this has to do with the problem,but please let me know. Thanks John Y
  • tomk2tomk2 Member Posts: 1
    I'm not sure of this, but I was told that a lot of it has to do with the military demand for diesel. Since most (if not all) military vehicles use diesel, and with 2 wars going on, the military is using more diesel than they would in a "normal" period. It's a simple supply and demand issue. :(
  • gagricegagrice Member Posts: 31,450
    Welcome to the forum
    Your take is logical. I don't know if we are buying diesel from refiners in the Middle East or shipping it from home. Good question to ask. I think a lot of the high price is the refiners are re-configuring to produce ULSD that is mandated this year. Some are already selling it, others are in the conversion process. That and the 3 refineries in TX that went off line in Rita did not help. May just be a combination of problems.
  • xabntroopxabntroop Member Posts: 7
    I received a notice in the mail about the update you just had completed, it says I may not be able to register my vehicle if I don't go get this done. I knew if it had something to do with registration that it could affect my Ca we're always re-inventing the wheel...I get fair milage but I'm worried about this thing...The notice gives me 3 years to have the update. :mad:
  • yrbenderyrbender Member Posts: 25
    Trying to get better mileage on my F250 asked the dealer about the larger intake and getting a 4 inch pipe to help air flow. He said both would void manufacture warrany and wait till after warranty period is over. Had a friend with a chip blow an enginer at 5k mile has to pay 15k for new motor no warranty due to chip. Anyone have any info on the intake or bigger pipe
  • stdbobstdbob Member Posts: 14
    What is the difference between on and off road diesel fuel? Off road is much cheaper.
  • cctdicctdi Member Posts: 82
    On road diesel is for the vehicles on the roads; passenger cars, light trucks, heavy trucks, buses. The dirt trucks, diggers on the mine field, farming trctors, heating oil are using the off road diesel which is colored with pigment. There is no difference between these two, but you are not allowed to use the off road diesel for the car on regular driving.
  • whisky6whisky6 Member Posts: 7
    Hi, this reponse to fuel of diesels my son had a 1999 f-250
    ford and one day we were driving around and checking the
    fuel mileage on the on board computor and we coasting down a hill and watching fuel mileage on the computor and we stopped believing what it saying when it got up to 55mpg
    so those little gadgets in these truck are a little off,thank,s
  • keuper20keuper20 Member Posts: 5
    for 6.0l owners be careful when thinking about a computer chip when trying to increase economy.if under warranty installing a chip may void your recommends using a cetane booster addative every fill.ive personally seen this addative increase fuel economy 10 mpg!!ford now also recommends changing BOTH fuel filters every 15k(6.0l).contact your local ford dealer for any questions.thanx.
  • huevosrancherohuevosranchero Member Posts: 2
    06 Ram 2500 Cummins 4x4

    Two weeks now with ~500 miles on the clock with mostly city stop and go driving and I am averaging 15.5 according to the trip computer. During a 100 stretch of highway, that went up to 18 driving a steady 70 (cruise).
  • stdbobstdbob Member Posts: 14
    Not trying to get away with anything, but am currious. Other than color why aren't we allowed to use it?
  • arrowstraparrowstrap Member Posts: 1
    it's dyed red so that when burned in an on-road engine it will bellow alarming colored smoke.

    other than the dye the only diffrence is that the on-road diesel is taxed and the off-road is not.
  • ruking1ruking1 Member Posts: 19,826
    Taxation is a main issue. However home heating oil and red dye farm diesel have GOBS (many more times 10x more in CA) more sulfur content. This of course pollutes more. (you are probably wondering why it is permitted given this fact? ME TOO!!)

    So for example in CA farm diesel aka red dyed diesel can have 500 ppm and more of sulfur vs 50 ppm on the road. In other states the ppm of sulfur is FAR higher. Again keep in mind the 2006 standard will be 15 ppm.
  • jbclawjbclaw Member Posts: 1
    don't know if this is still timely, but aero tanks in corona california has a number of large replacement and other tanks, they have a website and ship. I replaced 20 gallon forward tank in my F-350 with one of their tanks that bolted up and provided 45 gallon capacity, which they rated at 40, best wishes
  • lumberjackjmlumberjackjm Member Posts: 1
    I used dyed diesel (offroad diesel) in my tractor. I don't notice any unusual smoke.
  • ddf1ddf1 Member Posts: 18
    I know a lot of people running off road fuel in their personal vehicles around here. About the only way to tell if they are running on or off road fuel is to dip the tank or a sniffer. Because of the higher sulfur content. At start up on a cold engine there might be a difference but I don't think it is very much.
  • jim314jim314 Member Posts: 491
    Why would you not believe 55 mpg going down hill? In that case most of the motive force is gravity and there is no reason to question 55 mpg as the true mpg. If you take your foot off the accelerator and cost at a slower speed, you will get even higher mpg.

    Going up the same hill at 50 mph you might see the mpg gauge read 10 mpg. This could also be correct.
  • taointntaointn Member Posts: 2
    recently I've been researching some of the pros and cons of the vegetable oil possibilities. Does anyone have any personal experience of running veg oil through their diesel. I'm sure it will work in the short term, but I'm interested in the long term effects on plugs, fuel lines, etc...if someone has first hand experience.

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