Corrosion on bottom of fuel tank

Max_Florida · #1 09-22-2011, 06:40 PM

I pulled the fuel tank today and was cleaning off the bottom of it. There were three strips of some type of rubber that had either adhered on their own or were glued to the bottom of the tank. When I started pulling them off I noticed that there was corrosion under them in some places. One spot in particular was bad, so I kind of dug at it with a screwdriver since it was pretty soft. Sure enough I ended up with a little hole.

$405 for a brand new custom tank. I'm already way overbudget for the current round of projects, so I'm looking to get this fixed somewhat cheaply.

I called around and found a guy who will weld on a patch.

What I was thinking of doing was cutting off the bottom of the tank(leaving a 2" lip for him to weld to), cleaning the tank out and then having him weld on a new bottom.

Is there any reason not to go this route? Is the aluminum inherently corrosion resistant or does it need to be treated/coated? Is there a particular type of aluminum I need to use or will any "good" 1/8" aluminum do?

Blue_Heron · #2 09-22-2011, 09:28 PM

What you have is called crevice corrosion. Aluminum's resistance to corrosion comes from a thin layer of oxidation that forms on the surface of the metal and acts as a protective layer against further oxidation. But it has to be able to breathe to work. In a tight space where water can be trapped against the aluminum, you get the type of pitting you've got.

I wouldn't trash the bottom of the tank unless you've got large holes or the pitting is extensive. If you've got someone who can weld it for you, clean out all the pitting with a wire brush and let him weld over the holes and fill the pitting. Just make sure you get all of it. And before you start the process, make sure you clean the tank thoroughly to get all fuel and fuel vapor out. When I did mine, I emptied all the fuel, filled it to the top with water and a healthy dose of dawn dish washing liquid, and then filled it and drained it twice with clean water. By filling and emptying the tank three times, you can be sure you've purged all of the fuel vapor.

You will probably want to coat the tank before reinstalling it to protect against future corrosion. There are several options. I use epoxy resin and glass cloth, but there are more economical ways to do it.
Dave

abl1111 · #3 09-22-2011, 09:51 PM

Use closed cell foam strips or strips of lexan glued on the new tank. Water combined with little-to-no oxygen will allow aluminum ( most metals ) to corrode like that. Even if you keep water out, condensation over time will do it too. The strips are just to keep tank from sitting in any water - so Lexan will do the trick - BUT, the seal between the strips and the tank must be water proof !

I'd use a barrier coat of some sort, maybe InterProtect or similar on the new tank so aluminum is isolated even further.

I pulled my OEM tank, a '75, years ago and had the same thing you had. Cleaned it out, had it welded, epoxy coated it used closed cell foam strips - no problem. Looks like new !

Good luck

gofastsandman · #4 09-22-2011, 09:56 PM

Quote:

I pulled the fuel tank today and was cleaning off the bottom of it. There were three strips of some type of rubber that had either adhered on their own or were glued to the bottom of the tank. When I started pulling them off I noticed that there was corrosion under them in some places. One spot in particular was bad, so I kind of dug at it with a screwdriver since it was pretty soft. Sure enough I ended up with a little hole.

$405 for a brand new custom tank. I'm already way overbudget for the current round of projects, so I'm looking to get this fixed somewhat cheaply.

I called around and found a guy who will weld on a patch.

What I was thinking of doing was cutting off the bottom of the tank(leaving a 2" lip for him to weld to), cleaning the tank out and then having him weld on a new bottom.

Is there any reason not to go this route? Is the aluminum inherently corrosion resistant or does it need to be treated/coated? Is there a particular type of aluminum I need to use or will any "good" 1/8" aluminum do?

Cheap equals boom. If it is leaking, shut her down.

You have corrosion inside as well. You just can`t see it.

I push and squeeze food to look inside, but stiff things do not allow me that advantage.

Boom is not a good sound, and I know someone will say that I will never hear the boom. Too fast.

Me, not so much.
Cheers,
GFS

Bushwacker · #5 09-23-2011, 12:12 AM

Good thing you pulled the tank - I think you would have been smelling fuel in the bilge before long! Check out Coal Tar Epoxy for a coating - it's supposed to be one of the best coatings. And put the plastic strips on the bottom when you're done to keep it from sitting on a damp surface. Might want to have tank pressure tested after welding to make sure you got all the leaks.

77SceptreOB · #6 09-23-2011, 12:33 AM

I agree with GFS. Is your life something that is worth value engineering? I bought a new alum 100 gal tank and never looked back. my 2 cents.

strick · #7 09-23-2011, 01:01 AM

Quote:

There were three strips of some type of rubber that had either adhered on their own or were glued to the bottom of the tank. When I started pulling them off I noticed that there was corrosion under them in some places.

Rubber has carbon in it that reacts with the aluminum and causes the corrosion. This has been well documented and many people including myself have run into the same problem where rubber meets aluminum.

I would bite the bullet and buy a new tank so I could sleep better at night. There are some things on a boat you just dont want to mess around with...fuel tanks, hoses and fittings are one of those things.

strick

Blue197320 · #8 09-23-2011, 01:27 AM

$405 for a new tank, well i would be all over that if i were you. it will be worth it in the long run to know that your fuel system will not fail you. my new tank cost me about $1000 dollars. all i had was a little hole in the top of the tank.

Wildman · #9 09-23-2011, 08:38 AM

Replace the tank. Repair may buy you a few years, but then youll be in the same predicament again once the next crusty spot breaks through. Then you'll have to do ALL the work to pull it back out and still have to buy a tank.

Islandtrader · #10 09-23-2011, 09:34 AM

Where in FL. are you? I have a tank builder that does excellent work and fair prices. Let me know.

Check out the for sale section. Maybe the cost of tank and shipping would be a better deal for you now.

PS. put your location in your personal information it helps us all in answering questions.