Fuel Tank Leak???
 

So I have the motor out of boat for rebuild and found gas in bilge. Cleaned it up and went back in about 3 weeks later and another puddle of gas in bilge. Set up a test rig, blocked off fill and vent tube at the tank and threaded line into pick up hole with tee gauge valve. Was putting air into tank and when it got to 1psi there was a lot of creaking from the tank expanding so I bailed out. I guess my question is would there be any type of check ball or something in fill tube? Also did I set up my test correctly? I think the tank is leaking for sure because even at that 1lb. When I closed the valve it lost pressure pretty quickly. Going to check all my connections with soapy water for leaks so I can rule that out. Should I try to get the air in quicker to get to the 3-4psi test pressure? Started out with a air brush compressor and then got out my big compressor and set pressure to 20lbs. for filling but like I said I stopped at 1psi.

Thanks for any input in advance.

There should be an anti siphon valve on the supply line. Do not use any more than like 3 PSI to test the tank. There are very few reasons to have fuel in the bilge. If you have not spilled any, have a leaking hose(fill,vent or supply) or the sending unit gasket has failed, you have a bad tank.

Also a vacuum test would work as well.

An emissions smoke machine for evaporative emission systems works well also

I should be able to pump my air into the tank tho correct? The anti sipgon line would be on the supply line and not the tank itself?

It is usually the barbed nipple fitting at the 90* fitting on the siphon tube.

Finding gas in the bilge. Start thinking about a new tank.
All the sending units and fills and such are in the top of the tank. Unless you have it's super full and its been hot out these things will not leak.

Thanks everyone for all the responses. I guess I've been in leaky tank denial. Lol.. It looks like I will pull the bolsters and the back seat and pull up the carpet. Maybe there will be a panel over the tank but I doubt it being a 1990 boat. Any tips anyone can give to make this project as painless as possible?

Scott:

Let a qualified boat yard do the tank repair/replacment. It all depends what kind of tank (alum, galv. steel, fiberglass, etc) you have. This is nothing to fool with. Knowing how to repair the bedding that holds the tank properly and glassing it in is tricky if you do not do this work normally.

Wannabe

Thanks for the advice wannabe but the tank is 23yrs. old as well as the boat and I am replacing with new tank and going to tackle this project myself. Have a good idea on the project. Just looking for some tips on things to make the job easier, if there is a easy way to do this.

fixx
 

if you have to cut open the floor to get access drain the tank of its fuel and fill the tank with water b4 cutting with a power say so you dont ignite the fumes,also flush out the bilge with dawn soap and water..make sure all the compartments are open and have air moving through them..try not to be in a enclosed garage when cutting...once you get the floor removed you will have to dig out the foam to get the tank out,,i use a over head chain hoist once i get under the tank..when you built make sure you have the tank coated with coal tar epoxy,,it will never rot again..

Thanks mrfixxall, that is good advice. I did pump the tank out thru the pick up tube. Would that have enough of the gas out to fill tank with water or is there a way to get more out before I start cutting?

Maybe I am missing someting but there are many places that could leak fuel into the bilge without it being a leaky tank.

Check that there is in fact an anti siphon valve. There should be one but often if it plugged once, it my not have been replaced.

Check all fuel lines are dry, especially at connections. Tighten clamps but sometimes a rubber line can crack at the nipple, allowing fuel to leak regardless of how tight the clamp. Might need to remove lines, inspect and possibly cut off 1" or 2.
Fuel fliter dry and not leaking.

Pulling a tank can be lot of time and money. I would make real sure that was the problem.

You can take out the fuel sender and get the rest from there. Last tank I pulled I filled with water and flushed a bunch of times. There was still fuel soaked foam to deal with.

Pretty confident there are no leaks on the top side of tank. Everything is dry. Boat has been sitting with no motor since October and only had 17gal. of fuel in a 55gal. tank, so I'm pretty sure the fuel wasn't touching the top to leak anywhere. Going to double check all my connections on my pressure test tomorrow and retest.

you lost pressure quik from 1 psi. there is no question the contents of the tank are leaking. tip bow up and fill with water. you might see a thread of water running down from under tank. you need to fill it at least once anyway to flush out most of the gas fumes. i filled a bike tank 10 times and emptied. put torch over fuel neck and it still blew a 5 foot flame out. residual gas in the tank walls will still give you a free flying lesson. be careful. don't remember name but there is a good and reasonable tank builder around tom's river...

Still going to do one more test just to confirm before I start taking things apart.

Not to hijack your thread, but I have my motor out and have been toying with replacing the tank "just because". Not sure at this point.

take a look at the top of your tank. if you can see the whole thing, the job is doable. if it is buried under flooring? "if it ain't broke..."

I can see like a 16x16 area under the backseat. That will help with seeing where I am going to cut.

Did a final test on tank this weekend. Took it up to 4psi. Lost that in one hour. Took out interior tonight and will probably start on removing tank this weekend.

Carpet up and tank is empty. Going to fill with water and drain a couple times. Hope to have tank exposed over the weekend.

When I removed my tank, I cut along the inside edge of the stringers on each side of the tank. After digging thru all the foam I got the tank out and discovered there was a screw laying under the tank. Took it abt 15 years to rub thru and cause a leak. Found a welder that would weld an alum gas tank (that wasn't easy) and he welded it and press tested tank. After tank was back in, I glued, screwed and glassed some 1 X 1's to the inside edges of the stringers and re-used the portion of the floor I cut out (it was still in great shape). Glued,screwed and glassed the floor portion back in, lay'ed the carpet back down and walah. That was abt 15 years ago and it's still good.
Digging out the foam was the hardest part..

Well I got the tank out today. No foam holding it in which was great.

Did you find the leak ?

Yes.

Have same problem. Who makes new ones? 100 Gal.

I got mine made locally. Patriot Marine. Great work.

Where was the leak? What was the root cause?

starting this exact same project this weekend in my tantrum . makes me feel better to see someone else not afraid to do this themselves .

Leak was on the bottom where it meets the side. Tank was built in 1990 with the old standards. Only .090 aluminum. I've read that aluminum tanks have a life expectency of 15-20 years so it was due. New tank is .125 and is epoxy coated.

I hear you. I was pretty nervous about this project myself. Got a lot of good advice from some good friends. Project has gone pretty smooth so far.

What did the new tank run, replacing my 100 gallon soon and looking for a ballpark. I like the epoxy coating

My tank is a 55 gallon tank and came with fill, vent, 1/2" pick up tube, fuel gauge sending unit, ground lug and epoxy coating for $750.00.

100 gal will run about 1k.