Fuel spitting from vent, sometimes.

[Schmoe]

This one has me puzzled. '96 Marada 19ft, 3.0LX Merc/Alpha G2 setup. Filled the boat up Friday after getting it ready for the lake. Filled it slowly since I had to drive it over to the pump and didn't want gasoline (liquid gold) to go spewing out, as it has done this in the past before. Got finished and headed over to the dry stall to do some other things and let the boat sit outside in the sunlight. In the middle of the floor behind the driver and passenger seats, I noticed what looked like a 4X4 section of the carpet literally popping up. I had thought that since it was getting hotter and the boat was out in the sun, maybe the floor was warping a little and being that the boat is 13 years old. Well, I stood on top of it while checking the engine oil and then heard something spilling out, it was gasoline coming out of the vent hole. As soon as I got off of that certain spot inside the boat, the fuel quit pouring out. Took it on the water for a little bit and burned off some fuel and that section of the carpet was flush again and I could stand there without any fuel pouring out of the vent. When this intially happened while out of water, I had figured the vent pipe may have been clogged, so I slowly unscrewed the gas cap thinking it would be under pressure, but it wasn't. Any ideas?

 

[180shabah]

Re: Fuel spitting from vent, sometimes.

Let me get this straight - you had raw gas leaking inside the boat, and then decided the best course of action was to run the boat?

Ever hear of the Darwin awards?

If you have an internal fuel leak you need to get it repaired (and ALL of the spilled gas out of the boat) before opperating it again.

Go read Boats will explode

 

[collind]

Re: Fuel spitting from vent, sometimes.

Agreed, I would not even think about starting a boat with raw gasoline inside, especially from an unknown source. Lucky to be alive, fumes alone in the bilge become explosive!

 

[Schmoe]

Re: Fuel spitting from vent, sometimes.

Maybe I'm a little lost on the proper vernacular, but isn't the vent line right next to the gas cap on the OUTSIDE of the boat? Geesh, I'm not an idiot. I mean, I figured it was a vent line, it looks like a small protruding cap with a hole in the bottom of it, facing down. If you follow the line from the inside of the boat, it parallels with the fueling hose all the way to the gas tank. Am I missing something here?

 

[180shabah]

Re: Fuel spitting from vent, sometimes.

So clearing up a little - ALL gas that leaked went overboard (not good), and not internal to the boat.

That changes things a bit.

Fuel will expand in the sun light, but at no time should it exert enough pressure on the under side of the deck to force it up. It sounds like you deck has deteriorated to the point that the gas tank is all that is supporting it. This s a hole nother set of issues, as your gas tank is not designed to support any weight, that and the continued rubbing between it and the deck will create wear.

Perhaps some pictures, the deeck layout, any inspection/deck plates, tank mounting etc.

After this is solved, there is a device called the vent-whistle that will keep you from overfilling the tank. It installs in the vent line, as you are filling, the air that is escaping through the vent "whistles" when the fuel reaches the level of the whistle it stops. Then you stop before "spewing". It doesn't help with temperature expansion, but it does keep one mess under control.

 

[Schmoe]

Re: Fuel spitting from vent, sometimes.

Thanks. Never thought of that. No, the fuel didn't go overboard in the water, it was in the dry stall at the time. I inspected the boat last year for rot, but found nothing. But, you do bring up a good point. Obviously, where I was standing was on top of the fuel tank, which was expanding because of the vapor pressure building up, so there is no internal bracing between the floor and the gas tank. But my question, shouldn't that fuel vapor escaped from the gas tank via the vent line or at least when I opened up the gas cap? I mean, marine fuel tanks do vent, don't they?

 

[tashasdaddy]

Re: Fuel spitting from vent, sometimes.

you may have a clogged vent line. boat is 13 years old, may be time to change fuel lines. we now have ethanol in the fuel, which is known to soften old fuel lines.

 

[Schmoe]

Re: Fuel spitting from vent, sometimes.

That was my first thought, but then gas wouldn't be coming out of the vent line if it was clogged. That's whats confusing me. Also, if is was the vent line, wouldn't that pressure back up into the fueling hose and I would have pressure coming off of the gas cap when I opened it? This just isn't making any kind of logical sense to me.

 

[haulnazz15]

Re: Fuel spitting from vent, sometimes.

Okay I'm having trouble understanding this scenario. Lets get some things straightened out. The fuel tank in your boat is located under the floor where the "4x4" section popped up, correct? You then were standing on it, forcing any excess fuel out of the vent line (normal if it was that full). The gas couldn't go out of the fuel fill hose because there is a gas cap sealing it off, so it took the only other route to escape the pressure from you standing on it which was the vent hose.

I don't see anything wrong with any of this except that as you move down the road or across the lake, fuel shouldn't be leaving out through the vent line unless you over fill the tank, which you may have done. I would also keep an eye on the floor when you fill up to make sure that the floor doesn't raise when you fill it, thereby causing the same problem you experienced when someone walks on top of it. You could solve that problem by getting an aluminum fuel tank, or by adding reinforcement stringers a bit taller than the gas tank to keep pressure from affecting the fuel tank from people walking on it. Otherwise, just don't fill it up so much.

 

[Schmoe]

Re: Fuel spitting from vent, sometimes.

Thanks!!!! So, I'm guessing I have a plastic fuel tank? I did fill it up as much as I could that day. The fueling point is about head level when on the trailer and the fuel hose runs down to the gas tank at an angle from that point.

 

[allinmygarage]

Re: Fuel spitting from vent, sometimes.

21 Maxum SR 4.3

Somewhat similar thing happened to me this weekend. I posted a while back about my tank filling slowly at the gas station. So of course I got frustrated when filling it and basically went until gas was almost at the cap. Sure enough once on the dock people hopped in and the boat moved a little some gas poured out the vent. Only on mine it went into the lake

Anyway I would bet you overfilled it. At least that was my issue.

Your floor popping up makes no sense to me but I think I am still a little confused.

 

[Silvertip]

Re: Fuel spitting from vent, sometimes.

So the fuel went overboard out the vent. Yet it is apparent that the tank was expanding so much it raised the floor. Your investigation should be why was it NOT venting when the floor was raised. I think the relatively obvious answer is the vent line is pinched or plugged with something and it is venting only when extreme pressure is applied to the tank (as in standing on the bulge). That probably forced out whatever was in there (mud daubers perhaps). Inspection of the vent line is essential in this case and verify that it is really venting.

 

[haulnazz15]

Re: Fuel spitting from vent, sometimes.

Your floor popping up makes no sense to me but I think I am still a little confused.

He most likely has a plastic fuel tank under the floor. When the fuel tank is full/expands, it causes the plastic to bow up and this lifts the floor a bit. Once the fuel is burned (likely only a gallon or two) it will go back down to normal level.

 

[180shabah]

Re: Fuel spitting from vent, sometimes.

The fuel tank in your boat is located under the floor where the "4x4" section popped up, correct? You then were standing on it, forcing any excess fuel out of the vent line (normal if it was that full). The gas couldn't go out of the fuel fill hose because there is a gas cap sealing it off, so it took the only other route to escape the pressure from you standing on it which was the vent hose.

I don't see anything wrong with any of this

You don't see a problem with fuel tank compression caused by "standing on the deck???

 

[Mark42]

Re: Fuel spitting from vent, sometimes.

Yeah, something is not right. The deck should not be buckling up. There should not be enough pressure buildup to even begin to buckle a deck, regardless of how hot it was that day.

My guess is there is an obstruction in the vent line. Try disconnecting the vent from the gas tank and blowing air through it. Inspect the vent hose for wear or collapsing or kinking. Replace if anything appears not normal.

Lots of critters like to make nests in vent hoses. The actual hull fitting should have a screen on it. Inspect the fitting to be sure that the screen is not clogged.

And the deck has probably separated from the stringers at some point due to the expanding tank, so there is probably some structural integrity issues going on with the deck over the tank.

 

[salty87]

Re: Fuel spitting from vent, sometimes.

if he shot gas out the vent, it should be able to vent air now.

if you had to step away from the bulge to unscrew the fill cap, the pressure was removed so it wouldn't come out the fill line.

either way, if you were able to compress the bulge by standing on it...you've got deck problem(s).

 

[Schmoe]

Re: Fuel spitting from vent, sometimes.

Thanks for all the reply's, that's what I'm talking about! Deck is actually in good shape but now that one of ya'll mentioned it, there are about two screws on that section above the obvious fuel tank location that had been stripped when I was checking for loose screws/nuts/bolts, etc. etc. a few summers ago prior to setting up for the winter. That would explain why the floor "buckled" up. If those screws were not stripped, then I probably wouldn't be having this issue. The deck is in great shape and the boat has been stored inside and covered throughout it's life, never been in the rain and never parked in the water overnight...too many bugs out here. Maybe the former owner over tightened them and stripped them, he was a warrant officer at a maintenance batallion out here at Fort Sill and was maybe too anal about maintenance. When the floor is not buckling as last week, you can't tell if it's loose or anything, it fits snug and doesn't rattle. That particular piece has never come out. This was the first time I've ever seen that and also the first time I really tried to fill it up that much. I was trying to fill it to the brim as I know gas prices are going up and got it as full as possible. I have checked the vent lines for obvious damage or kinks, but all looks good and secure. I have not yet blown it out or taken it out to inspect it and there is a vent screen.

 

[haulnazz15]

Re: Fuel spitting from vent, sometimes.

Like I said, if fuel came out of the vent line, air will definetely come out too. The vent line is fine.