X15 cummins lugging?

Discussion in 'Peterbilt Forum' started by Edjahman, May 13, 2020.

  1. Edjahman

    Edjahman Medium Load Member

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    So I keep reading about ISX and dropped liners if you lug the motor.

    Apparently, the X15 suffers from the same issue.

    If I'm on flat ground, but fully loaded, is 1250 RPM in 18th gear OK if the engine is obviously not struggling?

    I keep reading about guys running at 1400 and above at all times apparently?

    If I had to run 1400 and above all the time then I can never use the 18th gear then.

    Advice?

    Thank you!
     
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  3. SmallPackage

    SmallPackage Road Train Member

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    Do you tend to find the engine needing more manifold pressure/boost at lower rpms to hold the speed? If so that is an indication that the engine can’t breathe and run free. Higher rpm’s may let it run a little easier and work less which means a happy bottom end and cooler liners. Nothing wrong with running in 17th all day if you don't have the legs for it. Running in Overdrive doesn’t always mean better mpg’s either.
     
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  4. Edjahman

    Edjahman Medium Load Member

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    I'll do some research and get back with you.

    Thank you.
     
  5. Wespipes

    Wespipes Medium Load Member

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    I tend to run in 8L instead of 8H. Puts me at around 1400 rpms. 8L puts me around 1200-1250. Seems to run better for me at least.
     
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  6. Dave_in_AZ

    Dave_in_AZ Road Train Member

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    Peak on my torque curve ISX is 1250. Itry and stay between 1325 and 1400.

    After 1400, fuel mileage drops off.
     
    Last edited: May 13, 2020
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  7. baha

    baha Road Train Member

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    Any time oil press. falls its time to change the oil, doing oil change at any time oil pressure falls will make motor last longer, use oil anil. to find out if its fuel in oil or just dirty oil making oil press. fall?
     
  8. Dave_in_AZ

    Dave_in_AZ Road Train Member

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    I've noticed when my oil is nearing the end of it's cycle, when it really gets cooking, it will drop about 2 or 3 pounds, and not bounce back to normal as quickly.
     
  9. Edjahman

    Edjahman Medium Load Member

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    If I'm running flat land and / light then 1250 - 1300 feels great.

    I just keep reading about this old liner problem with the ISX that is supposedly still apparent with the X15

    Thanks
     
  10. Edjahman

    Edjahman Medium Load Member

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    I'll run it 1250-1300 pulling light or flat land.

    It feels fine but I keep reading about the liner problem with the ISX.

    I guess the lugging issue may be when dragging heavy up hills etc.

    Thanks
     
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  11. Snow Monster

    Snow Monster Medium Load Member

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    Nothing wrong with having a going home gear.

    If you're empty or light or have a tailwind or it's downhill, like from Denver to KC, that extra gear can save you money.

    Personally, the only truck I ever ran down the road below 1500 rpm with a full load had a Cat engine in it, only because the limits were controlled by the computer.
    Truck ran 68 mph at 1350 rpm and got good fuel mileage, but if you read the manual Cat tells you to run at 1500 rpm or higher when 90k lbs or more, suspect Cummins says similar in their literature.

    Keep an eye on your gauges.
    If your temperatures, boost and pyrometer are on the low side, you're probably getting decent mileage.
    Some times you need to drop a gear and/or slow down a few mph in order to achieve this.
    Instead of torque'ing your way up a short hill at 1350 rpm, drop a gear and don't work the engine so hard, go part throttle instead of full throttle but one gear lower.
    If you're cruising at 1350 rpm and approaching a long grade, drop a gear before you start climbing to get into the higher hp range of the power curve.

    Just don't work the engine hard at low rpm's and you should be fine.
     
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