Cummins ISC overheats at idle **most of the time**

Discussion in 'Heavy Duty Diesel Truck Mechanics Forum' started by Mach, Dec 9, 2023.

  1. Mach

    Mach Light Load Member

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    This is an old problem that I've kind of just.. let go.

    2009 Cummins ISC "off-road spec" since 2011. Engine had a full in frame rebuild back in October of 2021 and ever since then, the truck would over heat at idle. We tried multiple thermostats (175* thermostats) , coolant flushes and new cooling lines but regardless of outside temperatures, the truck will eventually overheat at idle.

    If it's 80* out side, it will over heat in about 15 minutes of idleing and will stay at about 200* with the engine fan always running.

    If it's 10 degrees out side, it will eventually overheat after about an hour or more of idleing. The engine fan will keep it at about 185* in below freezing temps

    But here's the kicker. Every once in a while it won't overheat at all. Water temps even on the hottest days will sit at 175 to 180 and never rise above that when idleing. I can usually tell when it will or will not be "hot" just based off of hight the water temp is when driving.

    I have been putting this issue off because we could never find the issue, and using insite shows all temp sensors reading normal and there are no unusual hot spots on a temp gun indicating a blocked cooling passage that we can see.

    However the other day I noticed something. Was going to idle the truck through the night a few weeks back for heat since it was going to be a chilly night. I noticed that the truck was behaving and wasn't going to over heat and so I left the engine fan off all night and sure enough it was fine. Well the next day I shut the truck off to get loaded up and then restarted and went on my way. That night came and I was going to idle again but noticed it was running hotter and again, wanting to creep up while idleing. What I noticed though while laying in bed, was that the engine harmonics were different. You wouldn't notice it sitting in the driver seat or standing out side. But while laying there I started paying attention to it. It would have a very inconsistent vibration to it and it would come and go. Basically the harmonics were all over the place. But then when the engine is running cool and not wanting to overheat, it would idle smooth as butter with no inconsistencies in the vibration or anything

    I don't know if that helps out case in figuring out why it's like this but it's the only thing that I've noticed different when it's acting up, which is more normal than when it behaves.


    Any ideas?

    And yes the engine fan will always kick in and keep it from actually overheating, but that only happens at 220*. One day it didn't come on due to a failed water temp sensor and it actually tripped the high water temp alarm during idle. I had to jump in and hit the engine fan switch to cool it down.

    Thanks
     
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  3. Goodysnap

    Goodysnap Road Train Member

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    Water pump? Pull it and make sure the impeller is tight and does not spin independent from the pulley. Inspect the inlet and outlet of the radiator and main rad pipes as well as the water inlet to the engine for foreign object such as shop rags or plastic caps maybe left inside during overhaul.
     
    BoxCarKidd Thanks this.
  4. Mach

    Mach Light Load Member

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    Water pump is the only thing we haven't taken apart. I've since had a new radiator installed with new upper and lower hoses after the engine fan exploded on me last year. And the shop rag or something has always been my fear. But since we've gone though most major cooling lines, I'm kinda worried if it is a foreign object, it may be wedged in the water jacket of the head.

    But would any of that cause the engine to be fine one day, But as soon as you shut it off and restart, it could be running hot and "rough" for the next week before it decides to clear up? Not trying to dismiss what you are suggesting but just wondering.
     
  5. Goodysnap

    Goodysnap Road Train Member

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    Mechanical failures are usually more consistent or repeatable. If something is floating or moving around inside somewhere it could most certainly be more random.

    Please share the ESN if you have it and I can do some more digging. All Cummins parts used on the overhaul?
     
    JB7 Thanks this.
  6. Mach

    Mach Light Load Member

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    Knoxville Tennessee
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    46924665

    and yes all genuine cummins parts were used and it was a new head as well.
     
    Goodysnap Thanks this.
  7. Ridgeline

    Ridgeline Road Train Member

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    pull the radiator, pull the tanks off and clean it up the core.
     
    BoxCarKidd Thanks this.
  8. BoxCarKidd

    BoxCarKidd Road Train Member

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    Air in system? There is some air that circulates in the coolant all the time. Some engines have air bleed hoses from different areas on the engine back to a coolant surge tank and such. Others have a small bypass port for the thermostat and such.
    I could give an example or two but an air pocket in the cooling system can cause odd things. ( My bride says I go into to much detail, I am trying to do better ) Look for those.
     
  9. Mach

    Mach Light Load Member

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    Knoxville Tennessee
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    I think my best bet is to do the cleaning route. I'm going to guess that since the radiator and all the large hoses have been replaced since all this happened, there's something clogging a smaller line or even worse, a passage in the head. I'm gonna look into this here in January when we do some other work
     
  10. JB7

    JB7 Medium Load Member

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    I would pull the coolant filter and check and change it. Also pull the thermostat(s) and check there. For the smaller hoses you can blow air in the opposite direction of flow. See diagrams.
    Download - MEGA
     
  11. Mach

    Mach Light Load Member

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    Nov 19, 2017
    Knoxville Tennessee
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    Thanks. This is a ISC, not an ISX but the idea is about the same. Believe it or not but this engine actually doesn't have a coolant filter. But I'll still look into blowing through the lines with air when I drain the system next.
     
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