fuel tank vent?

[tonyjh63]

Could someone please explain this whole fuel tank vent thing to me? For some background, for a while now, every time I would put gas in my boat (1999 Bryant 182 Limited, and the fuel tank is up front) I would get this very strong smell of gas - as if there was a leak in the fuel line going to tank somewhere.
Anyway, a guy was working on my boat and I had him look at the situation. He said the problem was something about my vent line wasn't capped, so he went ahead and capped it for me. So, I picked up the boat this afternoon,stopped on the way home and put gas in the tank. While filling up, the gas spewed outward a couple of times as if I had overfilled the tank...I stopped for a second, then kept going (I knew it needed more gas than what I had already put in).
So...what causes the gas to spew outward like that (I was pumping the gas in pretty slowly)? And what about this putting a cap on the vent line?? I would have thought that a vent line would/should be uncapped, otherwise how would it "vent"? I checked it out while gassing up - there is a hose that runs up to the inside top, and it is capped off - so what is the point of this hose (vent line) anyway?
Thanks in advance!
Tony

 

[GA_Boater]

Gas spewed out of the filler because, get this, the vent is capped off.

The reason for smelling gas is the gas going in the tank which is filled with gas vapor, The vapor must be displaced or gas backs up through the filler. The smell is from the vent doing it's job, so you smell gas.

Is the vent near the filler? With no wind you may smell more fumes than usual.

Avoid whoever worked on your boat. He doesn't know his behind from a hole in the ground. The only way to cap the vent hose is to take it off the vent fitting and now the tank is no longer vented. If you use the boat it will starve for fuel and the motor will quit. Have you used it since the guy capped the hose?

 

[Lowlysubaruguy]

The thing to do if you can is to take that vent line and T it into the filler neck just below where the fuel nozzle goes in they make a special fitting for this that puts the vent just above where the actual pumps nozzle will be so the vent can be above that.

 

[GA_Boater]

Why do that. You also need a vented cap or closing the cap shuts the vent.

Hook up the vent hose the way it was before the guy capped it.

 

[tonyjh63]

^^^ But I don't know anything about this subject, so I don't know how it was before he capped it.
In fact, the reason I posted this question is that putting a cap on a vent hose sounds counterintuitive to me. I mean, how can it "vent" if it's capped??
And no, I have not run the boat since picking it up. It'll be Monday before I get a chance to get it to the lake...

 

[GA_Boater]

If it dies on you, open the fuel filler to vent the tank to get back to the dock/ramp.

 

[tpenfield]

Is this a below deck tank? I know of no reason why the fuel tank vent should be capped off. Maybe the guy working on your boat is an idiot :noidea:

When you re-fuel, are you smelling gas from within the boat, or just outside the boat?

 

[ahicks]

I agree that the tech who capped the vent line was a DA. I have to wonder if the original problem wasn't caused by over filling the tank? If there's too much fuel in the tank, as it warms it's going to expand, and if there's not enough room for that to happen within the tank, it's going to come out the vent.

 

[tonyjh63]

tpenfield - before my mechanic capped the vent, the smell was definitely from within the boat. Unfortunately, when I started pumping the gas into it this last time, gas spewed out almost immediately, so the smell was strong anyway, and I couldn't really tell from where the it was coming.
ahicks - honestly, I'm fairly certain I wasn't overfilling the tank, 'cause the last couple of times I got gas, I only put in a few gallons - I was actually testing to see if I was overfilling it. Also, the strong smell of gas was immediate - not really any time for the gas to heat up and expand. That's why I was worried that I might have a gas leak into the bilge and wind up catching on fire.
Is there any circumstance wherein it would be a good idea to cap the vent? Capping it seems very counterintuative to me...

 

[GA_Boater]

Is there any circumstance wherein it would be a good idea to cap the vent?

Never.

I think what happened is the vent hose somehow came off the vent fitting and your unqualified mechanic took the easy way out by capping the hose instead of reattaching to the vent fitting. It got rid if the smell. :doh:

I hope the mechanic isn't a family member.

 

[tpenfield]

tpenfield - before my mechanic capped the vent, the smell was definitely from within the boat. Unfortunately, when I started pumping the gas into it this last time, gas spewed out almost immediately, so the smell was strong anyway, and I couldn't really tell from where the it was coming.
ahicks - honestly, I'm fairly certain I wasn't overfilling the tank, 'cause the last couple of times I got gas, I only put in a few gallons - I was actually testing to see if I was overfilling it. Also, the strong smell of gas was immediate - not really any time for the gas to heat up and expand. That's why I was worried that I might have a gas leak into the bilge and wind up catching on fire.
Is there any circumstance wherein it would be a good idea to cap the vent? Capping it seems very counterintuative to me...

Leave the vent open so it vents (It vents to outside of the hull (right?)

Find the source of the gas fumes. You could have a hazardous situation.

Stay away from 'the guy'

 

[tonyjh63]

Ok, talked to the mechanic who capped my vent hose. Turns out, the cap has a tiny hole in it to vent. He said we can drill a bigger hole in it, but that the smell of gas will be right back. I told him I'm ok with the smell, as long as I know what's causing it. I just didn't want my bilge filling up with gas/fumes and wind up catching fire. I'm going to replace the gasket on the sending unit, and may also just take the cap off that vent hose during fill up.

 

[ahicks]

You need to get that vent venting overboard, whatever it takes.

 

[Texasmark]

Fumes sink and a lot depends on location of the vent and the prevailing wind at the time of filling. I have had the same thing happen many times especially when filling at a marina. I think the USCG requires some sort of venting for below deck tanks. I had a blower on my Starcraft I/O and just scoops on a Caravelle outboard. The Caravelle was the biggest problem as the vent was near the top of the Gunwale, amidship. Once refueling, you had to get out and do some running to get the scoops to get rid of the smell. Agree on the DOA of whomever capped the vent.

 

[tpenfield]

If you are smelling fumes within the boat, then you and your mechanic are missing something important.

 

[440roadrunner]

You need to get that vent venting overboard, whatever it takes.

I don't know much about marine regulations, but ^^THIS!!^^. I would be getting a mechanic to trace WHERE the vent line starts and ends and insure that NO lines coming/ going to the tank are cracked/ leaking, etc. The vent should most certainly NOT vent into the interior of the hull at any point. OVERBOARD!!