Air leak “whistle hiss” while idling- help

Discussion in 'Heavy Duty Diesel Truck Mechanics Forum' started by jgpixTrucking, Feb 16, 2020.

  1. jgpixTrucking

    jgpixTrucking Bobtail Member

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    Feb 16, 2020
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    Hello I have an International 4x6 daycab. My air tanks have been building pressure way too high 135psi. When it gets up to that pressure, you’ll hear a whistling hiss sound coming from under the cab. This noise will stop when air depletes , like pumping the brakes down. But pressure builds again and the noise comes back. Also, when I set the parking brake, I’ll have some excess air shoot out from under the cab for 10-15 seconds. This is new, the truck hasn’t always done this. Lastly I should mention that I lose about half the air in the tanks while truck is parked over the weekend. Your thoughts on what this could be?
     
  2. BoxCarKidd

    BoxCarKidd Road Train Member

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    Most likely a bad air governor to regulate pressure. Air lose is probably not related.
     
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  3. Minion120

    Minion120 Bobtail Member

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    I had a main airline burn off with the wires it was bundled with, they rubbed through and shorted out, result was a straight leak from the compressor, result was the same wierd spiking pressure built up and just about cooked my compressor. I had a bit of extra length so I could trim it out and used a quick connect to repair. Wires were a lot more involved, lol.
     
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  4. GFTLLC

    GFTLLC Bobtail Member

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    ☝️☝️ What he said. I'd definitely start here.
     
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  5. AModelCat

    AModelCat Road Train Member

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    If its holding half its air over the weekend I wouldn't lose sleep over it. The leak(s) are so small they aren't even worth wasting the time to look for IMO.
     
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  6. SmallPackage

    SmallPackage Medium Load Member

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    Sounds like a safety “pop-off” valve on an air tank could be letting the pressure out when it gets to high then reset itself when it goes halfway down. They are usually set to not allow pressure build up higher than 140-150 psi. in the system.
     
  7. lwlevens

    lwlevens Medium Load Member

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    #### my tri axle dump loses all the air over night.
     
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  8. jgpixTrucking

    jgpixTrucking Bobtail Member

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    Feb 16, 2020
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    Thanks. My mechanic says purge valve is stuck open but no clue why pressure is building so high all of a sudden. If it’s air governor related I’d want him to take care of that at the same time. I don’t like when stuff only gets fixed halfway then I’m spending additional days in a different truck
     
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  9. SmallPackage

    SmallPackage Medium Load Member

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    Governors are usually the first suspect in the cause of the pressure spike. And the surge/pop-off valve is doing its job in that case.
    I had one go bad that every time that day I’d hit a pretty good jarring bump on a rough ranch road it would pop-off at normal psi. I’d have to physically push it back closed then build psi back up then go down road till the next dang bump. That was a new one to me at the time. Replaced it that night and moved on.
     
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  10. AModelCat

    AModelCat Road Train Member

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    I've seen a gummed up governor cause purge valve to stick. If you've got an SKF air dryer I've seen those purge ports stick very often.
     
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