Fuel Tank vent?

The friendliest place on the web for anyone who enjoys boating.
If you have answers, please help by responding to the unanswered posts.

tcoop

Veteran Member
Joined
Sep 12, 2018
Messages
65
Location
United States
Vessel Name
Time To Play
Vessel Make
Nordic Tug 37
I have been having an issue while filling fuel tanks. Initially, the starboard tank was whistling and seeping fuel out the vent thru-hull, now the port vent is whistling and a little seeping just not as much as starboard.

I went below to see what I could and found a white plastic thing in the vent line on both sides. I am guessing it is a check valve but it is just a wild guess on my part.

The boat is a 2002 Nordic Tug 37. I would like some suggestions on what the white things are and what my next steps should be. I probably won't be able to make meaningful changes until we get farther north but I would like to have a plan of attack.
Thanks everyone.

IMG_2341.jpg

IMG_2342.jpg

IMG_2343.jpg
 
Looks to me like that's the source of the whistling noise. It's actually a whistle. I put them in my boat but mine look different, a different brand probably. The idea is when fueling you listen to the whistle and when it stops, shut off the nozzle. The tank is then full. Because diesel foams a lot, it will gurgle some first as the foam reaches the whistle. On my boat the vents are about two feet below the fills, that should be the other way around. Fuel will come out the vent before you have any warning that the tank is full. Possible $10,000 fine for that, hence the whistles.
I don't know why the vents would weep fuel other than a WAG that if you filled until fuel was at the vent outlet, the whistle might prevent it going back down to the tank. As the boat rocks some might spill out the vent. If you stop when the fuel hits the whistle it shouldn't do that.

And by the way I believe the plastic hose clamps are a no no, should be stainless.
 
Last edited:
Some tank vents have a low spot where fuel can collect and not drain back to the tank. They will then "spit" fuel when filling and vapors escaping... even when tank level is below the vent. If you havevaccess and can verify routing you may be able to shorten or reroute to eliminate the low spot. Many not that accessible and it is what it is.
 
Some tank vents have a low spot where fuel can collect and not drain back to the tank. They will then "spit" fuel when filling and vapors escaping... even when tank level is below the vent. If you havevaccess and can verify routing you may be able to shorten or reroute to eliminate the low spot. Many not that accessible and it is what it is.

That low spot holding fuel will eventually soften the hose and cause a weepy leak there. One of my sailboats did that. Best to route them so it's a straight downhill run.
 
Agree on the whistle. Should not have a check valve in the vent. Also agree on checking for low spots and the eliminating the low spots.
 
In the pix the whistles appear to be horizontal. The directions for mine said to mount them as vertical as possible or fuel would pool inside stopping the sound. That might be why one of yours was not whistling but now is. There was fuel in it that finally flowed out.
 
Those whistles are supposed to be oriented vertically. Looks like they have odd or no hose clamps on them. I advise to add some.
 
There's another current thread here about hose clamps where the AYBC standard is quoted. Those plastic ones are not compliant.
 
Cool when I know what to look for it is easy to find. I found Green Marine Fuel Whistle at Defender looks to be the same. I will check again but I think they are vertical. I will also check for any sags. I will also change the clamps. When I took the pictures I found one of the plastic clamps broken.
 
Yup, that is why plastic clamps are not approved.
 
Some tank vents have a low spot where fuel can collect and not drain back to the tank. They will then "spit" fuel when filling and vapors escaping... even when tank level is below the vent. If you havevaccess and can verify routing you may be able to shorten or reroute to eliminate the low spot. Many not that accessible and it is what it is.

Had that issue on a previous boat. Re routing the vent and cutting off extra fixed the problem.

Rob
 

Latest posts

Back
Top Bottom