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C15 air hissing oil fill cap?

Discussion in 'Trucks [ Eighteen Wheelers ]' started by Chevyho, Apr 17, 2016.

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  1. Apr 17, 2016 #1
    Chevyho

    Chevyho Medium Load Member

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    I noticed while doing an oil change on my 07 c15 acert yesterday I could hear a small air hissing sound from the oil fill cap with truck off and cap off. The compressor was replaced about a year ago because it was thought to be the cause of the air leak. It doesnt do it all the time, what could be causing this? Dryer check valve? Or is it normal? Truck runs good and builds air normal otherwise. Thanks for any help.
     
    Chevyho, Apr 17, 2016
    Chevyho, Apr 17, 2016
    #1
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  3. Apr 17, 2016 #2
    SAR

    SAR Road Train Member

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    I have a 06 mxs acert and mine will do that too but not all the time. I'm glad you mentioned this cause I thought there was something wrong with mine. I am curious also why it does that sound.
     
    SAR, Apr 17, 2016
    SAR, Apr 17, 2016
    #2
  4. Apr 18, 2016 #4
    Chevyho

    Chevyho Medium Load Member

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    How long has yours been doing it for?
     
    Chevyho, Apr 18, 2016
    Chevyho, Apr 18, 2016
    #4
  5. Apr 18, 2016 #4
    SAR

    SAR Road Train Member

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    It's been doing it ever since I owned it, for 5 years now. I actually just changed oil and I had put oil in it, started and rechecked the level. I had to add more and when I pull off oil cap it is releasing pressure out of it.

    It doesn't make much sense why there is pressure released out the filler cap and not out the blowby tube or dipstick.
     
    SAR, Apr 18, 2016
    SAR, Apr 18, 2016
    #4
  6. Apr 18, 2016 #6
    Chevyho

    Chevyho Medium Load Member

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    Well i think i just got mine figured out, with truck off when i removed the discharge line from compressor the hissing goes away. When i put my hand over the discharge line it xonitues to build pressure so im assuming dryer check valve is bad. Ill know in an hour.
     
    Chevyho, Apr 18, 2016
    Chevyho, Apr 18, 2016
    #6
    SAR Thanks this.
  7. Apr 18, 2016 #6
    SAR

    SAR Road Train Member

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    @GrapeApe i know you are knowledgeable on the Acert engine as you have some in your fleet do you experience this sound coming out the filler cap and if you do what would be causing this?
     
    SAR, Apr 18, 2016
    SAR, Apr 18, 2016
    #6
  8. Apr 18, 2016 #7
    GrapeApe

    GrapeApe Road Train Member

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    I have not run into that before, but 2 things come to mind. If the compressor outlet valve was not seating well (common on those compressors) AND the dryer check valve wasn't seating, air pressure could go back through the compressor and get passed the compressor piston rings and into the crank case. If only the dryer valve wasn't seating, the compressor outlet valve will stop it, so it needs to be both. If that's the source, it should not feed back if the compressor is unloaded because the discharge hose should be vented through the open purge valve at that point. This may be why it only happens sometimes, it depends on if the the compressor was loaded or unloaded when you shut it off.

    The other place that air can back feed the compressor is the unloader port, which comes right from the wet tank through the governor. If that's the source and the governor is working properly, you'd only hear it if there was enough air pressure to unload the compressor.

    This is what I'd do, when you hear the noise, pull the compressor discharge port and see if there is air pressure in it and if the noise stop. That's an easy hose to pull. If you don't hear the noise, try listening close to the dryer purge valve.
     
    GrapeApe, Apr 18, 2016
    GrapeApe, Apr 18, 2016
    #7
    SAR and Chevyho Thank this.
  9. Apr 18, 2016 #9
    Chevyho

    Chevyho Medium Load Member

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    Dryer check valve fixed it no more hissing. My check valve was missing its o ring. Mechanic at the parts place said that if the check valve is allowing air back to compressor its normal at high psi to go past the compressor rings, which is probably why I only noticed it when I would shut the truck off with air tanks right at 125psi.
     
    Last edited: Apr 18, 2016
    Chevyho, Apr 18, 2016
    Chevyho, Apr 18, 2016
    #9
    SAR and GrapeApe Thank this.
  10. Apr 18, 2016 #9
    Chevyho

    Chevyho Medium Load Member

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    I have an ad-ip dryer, so the check valve is on discharge line from dryer to tank. Quick check tho is with truck off to pull off discharge hose from compressor to dryer and after you initially pop it off and let whats in the hose escape plug it and it shouldnt continue to build pressure which is what mine was doing.
     
    Chevyho, Apr 18, 2016
    Chevyho, Apr 18, 2016
    #9
    SAR Thanks this.
  11. Apr 18, 2016 #10
    SAR

    SAR Road Train Member

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    Thanks for all the good information, when I get time I'll have to check out mine. I just thought this was normal and didn't pay much attention to it.

    Thanks for bringing this up chevyho.
     
    SAR, Apr 18, 2016
    SAR, Apr 18, 2016
    #10
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