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Fuel Venting Issue (causing incorrect fuel reading & motor to shut off)

Discussion in 'Technical Stuff' started by gnc1017, Sep 4, 2018.

  1. gnc1017

    gnc1017 Well-Known Member

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    Location:
    Carlyle Lake, IL
    This past summer, we had two instances where our motor had shut off without warning. Initially thinking our sending unit was bad and we were out of fuel (more on that later), we finally found that the tank was no longer venting due to a clogged vent fitting filter screen.

    We have a side-fill cap fuel system with the tank in the center toon and a carbon canister. From the tank, there are 2 vent hoses (one towards front and one towards rear of tank) that are Y'd together to a common vent hose under our port rear lounger (we have a RCW - center walk-out). This common vent hose connects to a check-valve assembly with another hose then dropping down from there to a carbon canister. The other end of the carbon canister vents through the deck floor below. My understanding is that this system is very typical on these newer boats (ours is a 2015). All of this on our RCW is located under and just behind our port lounger backrest (that backrest just pulls off as it was held on by Velcro).

    The end of our vent hose has a fitting that is screwed from above to the deck and flush with the deck on the underside. Once removed, this fitting has a small round black cap that screws off and a fine mesh screen just inside. Our vent screen was clogged with a residue (we're not sure exactly what yet - possibly evaporated fuel?), preventing the tank from venting properly.

    What transpired during operation was that the fuel tank would suck inwards due to the inability to vent - so much that the fuel level and gauge would still read quite high (would read ~ 7/8 full and then drop to ~5/8 after vented by removing the fill cap). This suction also in-turn even caused the sides of the tank to bend our fuel sending unit rod (this happened twice until we figured out what was really happening). Initially thinking we were fighting a bad fuel sending unit (until our second one also bent) we finally realized it was the venting issue that was causing the motor to shut down.

    I'm not sure if they still install the fine mesh screen in the end of the vent hose, but I'm curious if anyone else has this fine mesh vent screen and if so, if it is also clogged from some sort of residue. Most owners likely wouldn't realize it as our motor-shutdown issue only occurred after a full tank and then some lengthened run time. What we also now realize is that the amount of venting that comes through the fuel filler cap when we remove it is significantly less than it had been so thinking we have had this problem for a little while. So if you also experience a ton of air when you loosen your fill cap, you may want to check this component. If you check your system for a fine mesh vent screen, please post back your findings (does it exist and if so, is it clogged).

    Here are some pictures of what we found. I've also posted the pics in my profile Media.
     

    Attached Files:

  2. SEMPERFI8387

    SEMPERFI8387 Moderator

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    Interesting. I’ll have to check my GCW and see if I have this vent. I’ll pull it and check for cleanliness. I haven’t had any issues yet, but did notice last time I fueled up at marina, I had quite a vacuum built up when I opened my cap.
     
  3. gnc1017

    gnc1017 Well-Known Member

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    Location:
    Carlyle Lake, IL
    Thanks Semp! I'm figuring this to now be an annual maintenance item for us so very curious as to what you and others find.

    Looking back, we had the big 'woosh' from the cap for quite a while and now it is so much better. I have to believe we aren't the only one that has/had this happen, whether they realize it or not.
     
  4. the-little-B

    the-little-B Well-Known Member

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    I wws going to make a post about this yesterday bit didnt get around to it so I'll add to this one.

    Just went through a very similar problem as this but was a bit bigger problem. Mine is a 2018. The vent you have pictured was partially plugged with sawdust from when the hole was drilled through the floor but...the hole was drilled right on top of one of the aluminum frame cross members. Not only was the tank not venting properly , the result of the vent being on top of the cross member was it acted as a ramp if you will and pushed water right into the vent line! And that siphoned lake water right into the tank. Not good! The charcoal filter was full of water and the vent line had water in it right up to the tank vent itself!

    From day one it was difficult to get gas in the tank and I also got the "whoosh" when I'd open the cap and the last time the tank was sucked way in from the vacuum. After the boat dying a couple of times out on the lake , several tanks of gas full of water drained , and several filter changes , I have fixed the issue but what a pain it was!

    Another thing...my fuel pick up in the tank is low enough that it can just about suck the tank dry. So every little bit of water was going right through the system and would fill the separator , fuel bowl , and reservoir at the fuel pump in no time.

    The last time out I was able to fuel up with the gas nozzle at full speed and have no more signs of water getting into the system.

    Your issue I would think more common than the problem I had but could be the cause of a lot of the problems some are having with the slow fuel fill.
     
  5. gnc1017

    gnc1017 Well-Known Member

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    Location:
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    Little-B, can you confirm that your 2018 still has the same vent line cap and fine mesh screen that ours has? I'm curious if this is still the current design or if improvements have since been implemented.

    Also, from your indication of water intrusion through this vent, guessing you don't have the under-deck wave shield (and ours that has the shield doesn't have a risk of that issue)?
     
  6. the-little-B

    the-little-B Well-Known Member

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    Yes I have the exact same vent. Mine wasn't gummed up like yours and the mesh was actually pretty clean I'm guessing from the bath it got every time I took the boat out!

    I do have the wave sheild on mine too. Don't ask me how the water is getting there but the mis drilled hole is also right by the edge of the transom where it bolts to the underside. The wave sheild does have some minor gaps in that area so it's probably where it's coming from. Don't know if that's the norm or they got a little sloppy cutting out for the transom? The vent line needs to be towards the center of the boat/transom to keep it dry in my opinion. That and not having a cross member directing water right to it!
     
  7. gnc1017

    gnc1017 Well-Known Member

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    Location:
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    Thanks for following up Little-B. Since the vent line cap/screen appears common to several recent years, it will be interesting to hear if others are having any issues with gumming up/debris or water intrusion due to placement - or if ours are just isolated incidents.
     
  8. Oldchuck

    Oldchuck Well-Known Member

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    Location:
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    Since I have not purchased my boat yet, I would be very interested as to how common and on what models the vents are positioned like yours.. Any chance of a word from Bennington?
     
  9. Michiman

    Michiman Well-Known Member

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    GNC, thanks for taking the time to document, explain and provide pictures of the problem. I've got a 2016 GCW that has a similar if not identical setup but so far, no problems. That said, I think I'll try to take a closer look if weather permits before we put her to bed for the season.
     
  10. Oldchuck

    Oldchuck Well-Known Member

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    Location:
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    Again, Would like to know what models use this system and also if the-little-B is running at speed or a slow mover.
    Wondering is the water being forced up into the vent line and into the tank is caused by speed and is not experienced by slower boats with less HP..
     

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