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Get a new one, price of gas these days is almost the cost of a new 6 gal. tank filled.
Besides, you don't want to repair a plastic tank, just not worth the worry of explosion or other damage.
Dave

bscott wrote:So what do you do with a leaking gas tank
1) Weld it with a match--KaBOOM
2) Look into it with a match Byebye Bonnie
3) Have a few brewskies,fill it up and forget about it

Bob

Sue Kevin - - - you were just joking

Rick

I think you should weld it up. Then throw it away and buy a new one! Maybe salvage some of the fittings for possible future use, if storage of them is not an issue. Cut the bottom off and use it for an oil change tray or something, or bilge storage tray if you can get it clean enough.

I think the repair scenario is somewhat of an academic discussion, but if you are so inclined, take advantage of the situation to learn how to weld plastic on something that doesn’t matter. The walls are nice and thick, so they’re nice to work with. And then when something does come along (got vinyl seats?) and you have no other choice, you will have the skill to do it.

You will want to constantly watch that you don’t let the temperature get too high, or you will risk blackening/weakening the joint. You will also need to be sure that you penetrate all the way through the entire thickness of the wall, which is very difficult to do all along the entirety of the split on the inside of the tank. Harder still because the back is not easy to access.

You could probably do a good cosmetic job, but if the split is not to return, you will need to make it stronger than it was before, also hard to do, even if you build it up. The expansion and contraction of the tank (breathing) and normal flexing will open it again, next to the repair if not at it.

If it’s a poly tank, it’s not really a seam per se that you’re looking at, but a parting line where the two parts of the mould joined together imperfectly. Even though the mould parts are held under considerable pressure, the edges can wear and round, and dirt and debris can prevent them from closing completely, which results in a flash of excess material which is trimmed off, leaving the area thin, and weaker than the surrounding wall.

Because of it's naturally plastic, waxy nature (it does not have to have a plasticizer added to it, it's naturally "plastic"), there are no known effective adhesives/ solvent cements for polyethylene, so welding is your only real option for repair.

BTW – Ditto kmclemore’s procedure for cleaning as well. I might swish a ¼ cup of alcohol after the gas. Alcohol is miscible in both gasoline and the aqueous detergent solution that follows it.

Good luck!

BTW – Not to be flippant about it by any means, but a dose of reality is in order about the risk of explosion.

An explosion can occur only under a very narrowly defined set of conditions. The ratio of the fuel to air mix (the stoichiometric ratio, or lambda) must be within a narrow range or combustion simply cannot happen. Rinsing out and filling the tank with water will effectively prevent this from happening, but the weld area cannot be in direct contact with the water because it will simply disperse the heat too rapidly and prevent the weld from penetrating.

I safely welded up an old propane tank years ago, no boom boom. But others working around me were not as familiar with the laws of physics, so I did have a “blast” doing it just the same.

Kinda’ like the way some of you guys pull the ballast valve at the launch ramp, while saying loudly “time to empty the holding tank”.

I was doing some polyethylene welding for a customer app and recall the weld temp was about 220 C.

I believe the autoignition temp for auto grade gas is higher than this.

Filling the tank with water up to the weld point would take care of the fire risk nicely....after you gave done the multiple steps to remove the residual gas above.

After the gas is three months old you'll need a bigger match to ignite it "like maybe a blow torch"

So long ! J

So would some sort of epoxy or JB Weld work to reattach the threaded flange back to the top of the tank?

I would sure like to sail some more before I pull the boat home for gas tank replacement.

Thanks.

Jim

I do not know of any epoxy or glue that will successfully bond that plastic. The only way I know of is to weld it.

As for filling with water prior to welding, no, that won't work - the surface will be too cold and you'd never get the heat penetration you need to get a good weld, deep into the thermoplastic. As noted, after rinsing you should dry it out and let it air dry before commencing welding.

Trust me, once you've washed it thoroughly with detergent (twice) and followed the process I outlined in my posting, there is ZERO chance it will blow up. If you can smell gas, wash it again... if you can't there is no way in God's green earth that it can blow up, since you need a considerable mix of gas and air to get an explosive mixture, and you sure can smell that. I know this process works - I've welded and/or soldered dozens of gas tanks, and they were all cleaned in this manner and then welded with an open flame torch - I've not had a single 'ka-boom' yet. And here you're only using a soldering iron - no open flame, and at well below gas-igniting temperatures - so there is absolutely no chance it will explode.

As for swishing it with alcohol, although I agree it will mix with the gas, I don't think it's really necessary. Besides, you're just adding more potential fumes (alcohol) which are also flamable and as such I think it's a bad idea. Strong detergent will accomplish the same emulsion and it's entirely safe.

In a MacX there is a seam that was 5200 that others had problems in the fuel lockers leaking. They complained of water leaking in. Just Imagine gas leaking in the aft end interior of a boat and someone decides to light up a cig. while laying down in aft. berth reading a book.
If insurance found that a person welded a plastic tank.... for them as there would be no claim.
Like I said, replace tank.
Dave

I agree, Dave, replacing the tank is probably the best bet. I noted my repair method in the event that one might have to do this in a situation where one cannot get a tank (i.e. at sea), or where one cannot be sourced in the right size anymore.

DaveB wrote:In a MacX there is a seam that was 5200 that others had problems in the fuel lockers leaking. They complained of water leaking in. Just Imagine gas leaking in the aft end interior of a boat and someone decides to light up a cig. while laying down in aft. berth reading a book.
If insurance found that a person welded a plastic tank.... for them as there would be no claim.
Like I said, replace tank.
Dave

Dave . read a book !!
I was thinking more along the line of "Come On Baby Light My Fire "
where's Peaches when ya need her !
J

I also should have mentioned any retailer you bought the tank from will honor replacement.
They don't want Liability on them and usually take back no question asked.
I work with all types of Resins,epoxies and Plastics. Your temp heat method is great for temp. repair until replacement for a person with experance with heat generating tools for plastics, don't put your name on it.
It goes like this, I new a person that did this and this is how he did it. I can't recall his name.
Dave

kmclemore wrote:I agree, Dave, replacing the tank is probably the best bet. I noted my repair method in the event that one might have to do this in a situation where one cannot get a tank (i.e. at sea), or where one cannot be sourced in the right size anymore.

Is this forum takeing on a Political avenue?
Dave

Highlander wrote:Dave . read a book !!
I was thinking more along the line of "Come On Baby Light My Fire "
where's Peaches when ya need her !
J

I will be removing the hardware and cutting up the tank as the trash guys will not take it--then find a one piece 6 gal tank.
So who is peaches and what am I missing

Bob

Took a look at my gas tanks, made by Scepter, this morning. I expect the Moeller tanks to be made in a similar manner (got to be competitive ). They appear not to be made as individual units in a mould as I described above (envision inflating a giant fat plastic balloon inside the mould, using the filler opening to blow into).

It looks like they are made instead on a continuously-run line, with the tanks being pinched off into the moulds from a long plastic tube. While this would give a much higher production rate, this method would also leave a weak seam (and a “seam” in the true sense of the word) at the ends where the tube was pinched off, if the temperature and other conditions were not right for a good fusing of the material.

So Bob, if all manufacturers happen to be using this method, I would suspect that a truly “seamless” tank might not really exist on the market.

Regarding filling with water- note as I stated above that when you “fill” the tank with water, you don’t actually “fill” the tank with water. In order for this to work you need to leave some air space at the top of the tank in the area where you’re doing your welding so the heat doesn’t just disperse into the water. Any water film remaining on the inside surface of the material (be it plastic or metal) will quickly migrate away from the heat or evaporate. The obvious disadvantage of this method is you will have to deal with internal expansion from the heat, causing pressure to open the seam you’re trying to close. But of course if you clean the tank you won’t need to use water in the first place...

Does peaches smoke?