Diesel Leaking from Fuel Vent

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phild
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Diesel Leaking from Fuel Vent

Post by phild »

Apparently over the winter diesel fuel has been leaking from what I believe is the fuel vent (located roughly center of cockpit). Not just a few drops either, a very noticeable spill. I've always been careful to add a biocide keep the tank full over the winter to minimize water accumulation. I've never had any water contamination issues or anything like this. So what would cause diesel to leak from the vent while a boat is on the hard over the winter? Any thoughts would be appreciated. Thanks!
Phil and Mary DiDomenico
s/v Arabella
36094

"There is more to sailing than ropes and winches, cleats and bulging sails. There are faraway places and the everchanging light, and the silence, and a great peace at the bottom of your soul." - Mate
duetto
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Re: Diesel Leaking from Fuel Vent

Post by duetto »

hi,

most typically it comes from the fuel expanding during the heat of the day. if vent doesn't have a "pump overboard preventer" the fuel will escape thru the vent. don't fill quite as full next season.
john & diane cummings
duetto mv34 #23
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phild
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Re: Diesel Leaking from Fuel Vent

Post by phild »

Thanks for the reply. That was my first thought as well but this happen over the winter in the Northeast, tough to envision it getting that hot. Maybe I am underestimating the heating effect of shrink wrapping...
Phil and Mary DiDomenico
s/v Arabella
36094

"There is more to sailing than ropes and winches, cleats and bulging sails. There are faraway places and the everchanging light, and the silence, and a great peace at the bottom of your soul." - Mate
Loki
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Re: Diesel Leaking from Fuel Vent

Post by Loki »

Hi Phil, unfortunately I've had some experience with this.

First, to your PM question about raising fuel tank cover/cockpit floor. It should lift right up. If you've never had it up, its possible the black rubber foam gasket that runs around the edge had become one with the surface below, so some convincing might be needed. Its should be easy to replace if it gets trashed (the gasket, not the cover!). If I had this problem I'd be thinking roofer's pry bar and maybe a hacksaw blade to start the foam where you can get at it by the cabin door. Removal of the floor is really a two person job since you'll want to move it aside to fully inspect the tank.

There are several fittings - filler pipe, overflow preventer/air vent, two supply pipes and a fuel level sensor - any one of which could leak a small amount if the tank was filled to the brim. Leakage would make its way under the tank and out the drain in the middle, but the most I could see there is about a quart from the filler hose. If you put fuel in cold (say 50 degrees) and it heated to 80, thermal expansion would be maybe two quarts, not likely in New England, but definitely possible since we had a few hot spells this weird winter. It is possible for the fuel lines to siphon (if the siphon preventers are not installed or faulty) but I think the result there would be fuel in the bilge. (I can say from experience a bilge filled with diesel is not fun.)

What happened to my tank, however, was worse. The bottom of the tank corroded, leaving numerous pinhole leaks. This had happened in my old boat from a bit of perpetual water in the bottom, but the area was limited and I was able to get it repaired. On the PDQ, however, a significant area was corroded and the tank needed to be replaced. I concluded it was not from water inside the tank, but moisture from the outside as there was copious decayed organic matter trapped under the tank. I wanted to blame some design/manufacturing flaw, but it was probably due to my aggressive power washing of leaves!

The fuel was drained with a siphon hose that included a gas fuel squeeze pump. Removal was straightforward - my wife and I were able to wrestle it down and off to an aluminum fabricator who duplicated the tank, better than the original. It was a tad undersized to allow easy fit and drainage below. Quality anti-siphon valves (with spares) and level sensor were added and the installation was easy. All for about $1000, or one boat buck! Thinking back its possible the tank could have been repair with a "cold-welding" system like Durmetal, but I wasn't in the mood to haul it back and forth and try different solutions.

Hopefully your problem will be easier to solve - maybe a loose hoseclamp!
Jeff Morris, Loki 36072
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Re: Diesel Leaking from Fuel Vent

Post by jimlong »

I also developed a pin hole leak on the bottom edge of the tank.
I smelled gasoline while under the catamaran last year and checking the drain underneath verified that gas was leaking from somewhere on the tank. The floor covering the tank comes up readily as Jeff pointed out and once that is up the rest is pretty clear cut. My tank was sitting on small starboard shims at each corner which barely elevated the tank off of the floor. I'm inclined to think that the problem might be here as I also had lots of crud underneath that would prevent water from escaping thru the drain under the tank. Anyway, the gas was leaking thru a corroded pin hole on the bottom edge. I brought the tank to a tig welder to have it checked out and found just the one spot. After having it welded I clean it out several times with acetone and reinstalled it. Only this time when I put it back I used larger shims at each corner which raised it off the floor a little higher allowing better flow underneath, also epoxy-coated the bottom of the tank.
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