Secondary air pressure keeps dropping/fan turns kn

Discussion in 'Trucks [ Eighteen Wheelers ]' started by mhlvc, Jun 2, 2020.

  1. mhlvc

    mhlvc Bobtail Member

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    2016 579 Cummins ISX15

    Its 90+f and coolant gets hot really quick, and all of the sudden my secondary air pressure keeps dropping and engine fan keeps going on all the time.

    What could be the issue? Any ideas?
    Radiator?
     
    D.Tibbitt Thanks this.
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  3. D.Tibbitt

    D.Tibbitt Road Train Member

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    Idk about the air pressure but the fan coming on and off is normal on a hot day with the ac running
     
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  4. mhlvc

    mhlvc Bobtail Member

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    Now even when I idle more than 5min or so the secondary air pressure goes down and engine fan turns on.
    WTF is happening. I had this issue 2 weeks back and Kenworth/Peterbilt shops couldnt get it to act up so they didnt find out what the problem is
     
  5. mhlvc

    mhlvc Bobtail Member

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    I guessed so but man even going on a straight highway with a little hill - fan turns on. It wouldnt be an issue if my secondary air pressure didnt act up as. I have no idea what to do. Im at a PETRO right now but not sure if taking it in the shop here would do me and good. It is acting up currently so maybe they could find out what the issue is?
     
  6. magoo68

    magoo68 Road Train Member

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    Anyone look at fan hub to see if it’s leaking.
     
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  7. D.Tibbitt

    D.Tibbitt Road Train Member

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    How much psi are u losing ? i wouldnt worry about the fan coming on and off. That is normal . with ac on and it hot outside its going to repeadtly come on every minute or so
     
  8. mhlvc

    mhlvc Bobtail Member

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    I literally just keeps going down, so a lot. It mostly happens when downshifting, but now even when I idle it happens it seems.
    I did put new air lines, but even when not hooked up to a trailer it happens. Could it be anything computer related or electrical/fuses/relays? Peterbilt did computer/engine software updates so idk
     
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  9. SmallPackage

    SmallPackage Road Train Member

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    Sounds like the fan hub or the solenoid to control the fan. Or the air line between the solenoid and hub is leaking.
     
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  10. mhlvc

    mhlvc Bobtail Member

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    Will get that checked out. How safe am I to drive through the night and tomorrow where Ill take to to a local shop? Temps did drop down to 60s
     
  11. BoxCarKidd

    BoxCarKidd Road Train Member

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    How low does the air pressure go before the fan kicks on? How low does it go at the most?
    If it does it in the parking lot maybe try this. Turn the key off to stop the engine and noise. Turn it back to the on position. Then get out and try to find an air leak.
    If the engine is never over 220 for a short time and air pressure under 90 I would rock on. Better to fix it if possible. If the fan hub is leaking air and is air disenguaged cap off the line somehow and get home.
     
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