Air vent from main water tank seems clogged

Discussion in 'General Discussion' started by JeffMac, Nov 6, 2018.

  1. northern

    northern Well-Known Member

    Jan 17, 2007
    West coast Vancouver to Alaska
    380 Aft Cabin 1989 GPS and Charts by Nobeltec
    Twin 454 strait shaft
    We have a water maker on the boat. When I was checking water level I noticed the sides of the tank were bowing out. I loosened the fill cap and a lot of compressed air came out. I then took a thin wire and put it into the over flow below the fill port on the outside. I got stuff out of the overflow. There was no screen in the overflow. Before I put the wire in I could not blow into the over flow after I could.
     
  2. MonacoMike

    MonacoMike Well-Known Member

    Sep 15, 2009
    Indiana lakes and Lake Michigan
    2000 Cruisers 3870
    97 270 Sundancer
    85 Sea Ray Monaco 197
    8.2 Mercs,
    7.4 BII
    260hp Alpha 1
    I believe simple tank expansion would happen first, then back flow.

    MM
     
  3. JeffMac

    JeffMac New Member

    22
    Nov 6, 2018
    Seattle, WA
    320 Sundancer, 2004, twin v-drives
    350 Mag 300 hp inboard
    Amazing input everyone. I’m the OP. Here is some more info.

    First, this is still a mystery.
    I took off the vent hose both where it enters the tank, and where it connects to the stainless steel valve in the hull. I was able to flush water in both directions and also breath into the hose comfortably from both sides. It felt like I was snorkeling, which tells me it flows well. Next, I removed the stainless steel fitting that goes through the hull. It has some little metal screens in it. All was clear, no obstruction. Next, I removed the fitting that connects the vent line to the actual water tank. It was clear as well. Lastly, checked for any kinks in the vent line and there were none.

    So, as it stands now, when I fill water into the tank it expands significantly (breaking the wooden enclosure). No water exits the vent and I don’t even feel any air exiting. The tank just swells.

    My current workaround on this is to just fill my tank to 3/4 going forward because I can’t figure out the issue.

    Anothe theory mentioned above is an issue inside the tank itself. That may be the issue. Not sure.

    Can’t thank all of you enough. Any other thoughts? I’m all ears

    Here’s a question I should have asked: Is the water vent intended to allow excess water to drain out if I overfill the tank? Or, is it merely for air to pass in both directions?

    Here is the next test I plan to conduct today... With the water vent line removed, and the fitting that goes into the tank removed, I'm going to fill more water into the tank from the fill cap. If excess water comes shooting out of the tank through the hole where the vent typically connects, then I know my problem is somewhere in the vent line or the fittings. If water doesn't come shooting out then I know my issue is inside the tank itself. However, this all assumes that water is designed to exit the water tank through the vent hole. Perhaps it's only meant to transport air (see question above)..
     
    Last edited: Nov 7, 2018
  4. MonacoMike

    MonacoMike Well-Known Member

    Sep 15, 2009
    Indiana lakes and Lake Michigan
    2000 Cruisers 3870
    97 270 Sundancer
    85 Sea Ray Monaco 197
    8.2 Mercs,
    7.4 BII
    260hp Alpha 1
    That is very odd.

    MM
     
  5. Lazy Daze

    Lazy Daze Well-Known Member TECHNICAL Contributor

    Apr 21, 2009
    PA
    Various
    Various
    The vent is a simple tube - nothing more, nothing less. So, yes, excess water will escape the tank via the vent line. Excess water will fill up and overflow the vent line before it does via the fill line since the vent line is smaller.

    OK, here are some things you can try to further narrow down the variables. I realize you have sort of already done some of these - but doing these in a different way may help shed some light.

    -- With the vent line removed, try filling the tank. Same results = issue with the fitting or just inside the tank. "Normal" results = issue with the vent hose/hull fitting.
    -- Remove the hose, again, from the hull fitting. Blow/suck through the hose. It should "feel" about the same as with the hose removed from the tank fitting (which you already did). Or, suck/blow directly on the fitting or use a short length of extra hose that you may have laying around.
    -- Try poking something, like a zip tie, through the tank fitting.

    From what you have done, though, it seems like there is an issue with the fitting in the tank

    EDIT: Just saw the last paragraph in your most recent post and looks you're planning on doing some of things I thought of, as well.
     
  6. Woody

    Woody Well-Known Member

    Nov 20, 2007
    N. Wisconsin/Lk Superior
    2005 420DA
    Cummins 6CTA8.3
    Your physics teacher would be unhappy with you. His water tank vent will have water coming out before the fill hole will because it's lower. If you stopped filling at any point before that the water level in both hoses would be the same regardless of dia.
     
  7. Lazy Daze

    Lazy Daze Well-Known Member TECHNICAL Contributor

    Apr 21, 2009
    PA
    Various
    Various
    :)

    Funny... I wasn't even thinking about that (water will always find it's own level) as I wrote that reply. Which, of course, is true. However, because the water is being forcefully introduced into the tank, I do think the vent hose fills up a bit faster. The only reason I say that (and what was on my mind when I replied) is because I've filled up tanks where the vent and fill are at the same height (within the same deck plate) and I see spurting from the vent before it backs up the fill hose. Now, I've only ever done that a few times, and it's been a while, but that's what I "seem" to recall.

    To be honest, it does make more sense that they would still fill up at the same rate... but I do remember seeing that vent hose spurt first. But again... it's been a while...
     
  8. JeffMac

    JeffMac New Member

    22
    Nov 6, 2018
    Seattle, WA
    320 Sundancer, 2004, twin v-drives
    350 Mag 300 hp inboard
    update... the problem appears to be in the tank itself. Something about it is not allowing air or water to go into the vent tube despite a clear tube, clear fitting, clear hull piece. So, the good news is that as long as I just fill the tank to 3/4 full I don’t have any risk of it expanding and breaking the wood enclosure like before. Also, I tested for potential implosion by draining water from a sink and after draining about 3/4 of my tank I was satisfied that there is no implosion risk. So, let’s call this mystery “solved” for now. Thanks again for the all the ideas.
     
  9. Woody

    Woody Well-Known Member

    Nov 20, 2007
    N. Wisconsin/Lk Superior
    2005 420DA
    Cummins 6CTA8.3
    Jeff, you can't do this to us. One of the benefits of this website is we all get to learn something from the other guys headaches.

    I've read this post and have even more questions... If the tank vent doesn't work, how can he pump 30gal of water out, the tank should be crushed. Why does his tank expand enough to damage the wood enclosure that's around it?

    We need pictures of that tank and enclosure and the bulges. We need to figure this mystery out, it'll be satisfying. It just ain't fair to us if you call it 'solved' prematurely. The CSR group doesn't allow premature jubilation, we finish the job.:cool:
     
    techmitch and Great Lakes like this.
  10. LUnaCY

    LUnaCY Member

    71
    Aug 28, 2018
    Afton, MN
    310 Sundancer 2002. Mercruiser 5.0 MPI Bravo III
    Mercruiser 5.0 MPI Bravo III
    Yup...Once you “defer” a maintenance item you may as well let it sink.

    (Maybe a bit drastic)
     
  11. MonacoMike

    MonacoMike Well-Known Member

    Sep 15, 2009
    Indiana lakes and Lake Michigan
    2000 Cruisers 3870
    97 270 Sundancer
    85 Sea Ray Monaco 197
    8.2 Mercs,
    7.4 BII
    260hp Alpha 1
    Agreed!

    MM
     
  12. JeffMac

    JeffMac New Member

    22
    Nov 6, 2018
    Seattle, WA
    320 Sundancer, 2004, twin v-drives
    350 Mag 300 hp inboard
    I will let you know if I discover anything else on this mystery. For now, I reattached everything and closed up all of the places I had opened to gain access to the tank and vent hose. Sorry we don’t have full closure on this! It really is weird and the fact that it’s my first boat and I’m not very handy doesn’t help. At least I’ve confirmed that this is highly unusual.
     
  13. MonacoMike

    MonacoMike Well-Known Member

    Sep 15, 2009
    Indiana lakes and Lake Michigan
    2000 Cruisers 3870
    97 270 Sundancer
    85 Sea Ray Monaco 197
    8.2 Mercs,
    7.4 BII
    260hp Alpha 1
    Good luck.

    MM
     
  14. Brett H

    Brett H Member

    144
    Dec 12, 2009
    Lake Lanier, GA
    2004 550 Sundancer w/ MAN's - Unleashed
    Raymarine e127's; KVH HD7; Xantrex 3024 Inverter
    T-800 MAN's (D2848LE403)
    FWIW, using the vent in conjunction with the fill cap off, you should be able to use a shop vac as a test tool to purge by pushing or pulling air/water through the water system. Using it to suck or blowing from either fill or vent could achieve various results. Typical shop vacs shouldn't have enough power to do any damage.

    I would first try sucking from the vent to see if air (if tank isn't full) or water (if tank is full) is coming out the vent and/or air seems to be going into the fill. This may flush foreign matter described by others from the vent outlet. Then I might try blowing into the fill to see if air (if tank isn't full) or water (if tank is full) is coming out the vent.
     
  15. Blueone

    Blueone Well-Known Member SILVER Sponsor

    Jan 24, 2007
    Lake Erie, Ohio
    2004 420 Sundancer
    Cummins 6CTA 450's
    That just doesn't make sense. The tank is a big empty box with maybe a baffle or two but I doubt it though. Something has to be blocking the vent tube. Maybe its floating near it or stuck to the opening and closes it off when full.... but still if you were filling fresh water and the vent was plugged it should backflow out around the hose and not bulge the tank. You have to be missing something obvious on such a simple system.

    320 water tank.png
     
  16. dwna1a

    dwna1a Well-Known Member PLATINUM Sponsor

    Apr 23, 2012
    James River
    88 Weekender 300 "Seahorse"
    Twins 350
    Jeff, this may sound weird and the guys may fuss at me.

    Go over to the pump out station and suck the water out of the tank. You should hear air being pulled into the tank thru the vent. Some thing is being pushed to or near that fitting and blocking it. I also agree with removing the tank fitting cleaning it and cleaning the hole into the tank. If it's easy to get to all these fittings and hose think about replacing it

    It's just a idea and I may be way off base with it.
     
  17. MonacoMike

    MonacoMike Well-Known Member

    Sep 15, 2009
    Indiana lakes and Lake Michigan
    2000 Cruisers 3870
    97 270 Sundancer
    85 Sea Ray Monaco 197
    8.2 Mercs,
    7.4 BII
    260hp Alpha 1
    Mechanically I get what you want to do. From a sanitary side, gross. LOL

    MM
     
  18. Blueone

    Blueone Well-Known Member SILVER Sponsor

    Jan 24, 2007
    Lake Erie, Ohio
    2004 420 Sundancer
    Cummins 6CTA 450's
    I doubt the fill inlet in the tank goes to the floor of the tank.... plus the sanitary issues
     
  19. Sublimetime

    Sublimetime Active Member

    501
    Oct 22, 2007
    clifton nj
    420 da
    454

    use the shop vac as mentioned earlier.
     
  20. dwna1a

    dwna1a Well-Known Member PLATINUM Sponsor

    Apr 23, 2012
    James River
    88 Weekender 300 "Seahorse"
    Twins 350
    I told you it was off the wall suggestion

    Unless you have a commercial grade shop vac I'm not sure it would be able to make it pull that much of a vacuum.
     

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