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Diesel Questions and Problems in General (non specific makes)



  • muncymuncy Posts: 10
    how can you tell which glow plugs are bad with out changung all of them
  • MrShift@EdmundsMrShift@Edmunds Posts: 43,626
    It's best to change them all, like spark plugs. They wear out.
  • orchiddjorchiddj Posts: 13
    On my 1990 the glow plugs are easily removed like a spark plug. (My book says on some models you have to remove valve covers to get at them) it probably would be best to replace them all. You can test by pulling the glow plugs and connecting to a battery. The end will “glow” also it will get very hot. It only takes a few seconds for them to heat up. If any do not heat up they are bad.

    I would test before replacing. I almost just replaced mine. After testing found all were good and that was over a year ago.

  • MrShift@EdmundsMrShift@Edmunds Posts: 43,626
    I've read that they should be replaced somewhere around 100,000 miles, give or take.
  • wisdodgewisdodge Posts: 6
    I have a 2004 Dodge Diesel. I bought it for towing a 35-foot travel trailer. I talked to several Dodge owners before I bought mine that were towing travel trailers and they always said they get 18 MPG towing. Mine only gets 10-11 MPG. After two years I decided to put in the Bully Dog chip and I didn’t see a difference. Last year I added the K&N filter and I still didn’t see a difference. This year I had them change the muffler and I still don’t see a difference. I also went by the onboard MPG calculator and I now realize that with the chip it’s no longer accurate. I will re-check my MPG again but calculating it by hand.
    The big question is why am I not getting 18 MPG? Is there something I am missing?
    Is there that much of a difference between engines? It does have a lot of power to tow the trailer. This last week towing the trailer I hand calculated the MPG and it was 10.2 MPG. The onboard computer showed 13.
  • MrShift@EdmundsMrShift@Edmunds Posts: 43,626
    Probably you are relying on anecdotal information from other owners, and anecdotal information can be very tricky to confirm. For instance, maybe one day one time in ideal conditions someone got 18 mpg, and then they presume to declare this the standard for the truck. Also if you have a different rear end ratio, or dual tires, this can have a big effect. And then there is the matter of what type of terrain you drive in, vs. the report from the other owners. So a guy in Kansas with a 3:55 ratio rear end is going to perform a lot better than someone in Colorado with a 4:10 rear end.

    Your reports on chips and K&N and fancy mufflers only confirms my skepticism that while these things might make the car run better they are not likely to increase fuel mileage.
  • KCRam@EdmundsKCRam@Edmunds Mt. Arlington NJPosts: 3,495
    In additio to Shifty's reply, it's also important to ask what year those other Rams are. The old mechanical 12-valve engine (used until December 1997) was phenomenal on fuel... my 1996 3500 extended cab dually 4x4 had no problem getting 24 mpg empty with the 3.54 axle. My 2005 3500 Quad Cab 4x4 dually requires a lot of effort to get 20 mpg with 3.73s under the same conditions.

    kcram - Pickups Host

    KCRam - Pickups/Wagons/Vans+Minivans Moderator

  • cayadopicayadopi Posts: 12
    4:10 ratio here, '92 Ford F350 dually, Int'l 7.3 diesel.

    When I do mileage checks, I fill the tanks to the very top, so I have a consistent starting point.

    I was wondering also if there was a difference in mpg in various states based on their fuel mixture or something. I pulled my 37' RV from FL to NM recently. In the hilly area of FL I was getting 11mpg when towing a lot of weight - which was pretty much consistent in the flat and hilly areas in FL over many years. The further west I went the worse the mpg got, with a low of 7.3mpg in western TX and across NM (I-10). I didn't think the short times I had to downshift for hill climbing would have affected the mpg. The hill country N of San Antonio and then west for a while required more downshifting (9mpg area), compared to W. Tx and NM, which seemed flatter with fewer steep hills/mountains.

    I used to get 18mpg consistently in combined traffic (city/highway) until a few years back (16mpg). It's hard for me to imagine any p/u truck getting 18mpg towing a big rig.
  • MrShift@EdmundsMrShift@Edmunds Posts: 43,626
    Well it's no accident that places like Texas are good for wind generators. Headwinds can really knock down mileage on a towing rig.

    I kind of agree with the other posters---in the final analysis, fuel mileage on this or that diesel truck is kind of "genetic"--it's going to get what it was built to get and driving habits are probably the best way to get any improvements.
  • wisdodgewisdodge Posts: 6
    Thank you everyone for your input. I drive on fairly level roads. I hand calculated my mileage to and from work the past two weeks, not towing and empty, and with the outlook computer set to stock I get 18.4 MPG and with it set to towing I get 18.39 MPG. Not much difference. Now this is in heavy traffic with a lot of stop and go, some times at speeds of 62 MPH. I wanted to check this quick before I tow my trailer out to Colorado for a week leaving July 26. I was hoping to see an increase in the MPG in the tow mode compared to the stock. I Believe I have the 3.73 gears. I was wondering if the others had the 4:10 gears that were getting the better mileage. I used to have an F150 with the 3.02 gears and it didn't have the power to tow a small popup camper. I changed them to the 3.73 gears and my MPG jumped from 12 to 18 and I had no problems towing anything. I was told that the 3.02 gears kept the engine at a bad power range. I wonder if the same is true here with the 3.73 vs 4.10 gears. From now on when I ask about their gas mileage I will have to ask which gears they have.
  • MrShift@EdmundsMrShift@Edmunds Posts: 43,626
    It is my understanding that when you have engines of considerable horsepower and torque, that ONCE they get moving and develop some forward momentum, from that point on, you wouldn't see that much difference in fuel economy if you just added another few thousand pounds to an already moving truck. Does an 18 wheeler empty vs. one with a few thousand pounds in the back on a flat highway really change its MPG? I doubt it.

    Sure, if it were fully loaded with 10 tons and churning up a hill---yeah, that would eat up fuel, but for a pickup truck towing a trailer, once it got moving, I'm not surprised your MPG is close with or w/o the trailer. I'm sure that in traffic and stop and go, your MPG difference would be much more noticeable.
  • wisdodgewisdodge Posts: 6
    Normally I would agree, that is why I don't understand why the mileage drops so much. Most of the time I tow the highway is fairly flat, a few small hills. That is why I wonder if the gear ratio is the big difference. I would assume the 4:10 gears would hurt the gas mileage not help.
    Thanks for all your input.
  • MrShift@EdmundsMrShift@Edmunds Posts: 43,626
    Yes lower gearing would eat up more gas (but give more low end pulling power); also there might be an aerodynamic factor at play, depending on whether you are pulling a Bullet or a Cinder Block. :P
  • wisdodgewisdodge Posts: 6
    Yes, my trailer is a big box, which doesn't help. Last year I towed my brothers 12' V nose trailer with a couple of 4 wheelers and It didn't seem to get any better mileage. I didn't hand calculate the mileage but the onboard computer still had the same reading as my big trailer. I was surprised because I couldn't even tell his trailer was back there. I thought for sure I would get 20 MPG on that trip. He has a gas truck and he gets 18 pulling it.
  • galena50galena50 Posts: 3
    We are looking at a RV that uses the International VT360 diesel engine. I cannot find any HP versus torque curves for the 300HP engine. Anyone know where I can locate the curves for the 300HP engine?
    Thanks :)
  • I towed the trailer from Wisconsin to Colorado and back a few weeks ago. I figure I averaged about 10 MPG and I kept my speed about 68 to 70 MPH instead of 75. My brother in-law then towed it out to South Dakota using a Ford F250 diesel that he borrowed. It was a stock truck, no chip or K&N air fileter. He said he only got about 6 MPG and he said he was going about 65 MPH to try and get the best MPG that he could to try and beat my milage.
  • fphilli1fphilli1 Posts: 30
    2001 7.3 Excursion no start. It started this morning, hooked up my trailer harness and started fine. After we did some rewireing on the trailer harness it did not start. I unplugged the trailer harness from the truck and it did not start. It cranks good but will not light. I have replaced the CPS last year due to recall. It has never done this before.
    What fuse or relay should I check. It have fuel and when I turn the key on I can hear the fuel pump/relay run.
    I have disconnected the battery terminals twice to try and reset the moduel. Help!!!! :sick: :sick:
  • MrShift@EdmundsMrShift@Edmunds Posts: 43,626
    Glow plug relay would be a good start and the CPS is troublesome on these, as you know.
  • fphilli1fphilli1 Posts: 30
    ;) Thanks for the reply. It was a 20amp fuse. The fuse circuit was for the cigar lighter and data. The data communication fuse blown will cause a no start.
  • MrShift@EdmundsMrShift@Edmunds Posts: 43,626
    One wonders why a 20 amp fuse would blow, so this may not be the end of the story but I hope it is for you.
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