Jumper K. Balls
Jumper K. Balls UberDork
1/23/17 1:38 p.m.

The0retical's post and the fact that I had one needing to be done seemed to align. So I figured I would share how I usually do it. Others may have other methods. So do I, but this all this tank needs.

First installment:

This here is a fuel tank from an old Fiat

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It is actually in really nice shape, but to see all of the issues it needs to be clean. The easy button for me is to send it to a local company who specializes in acid dipping cars. I give them $60-100 depending on the tank and get it back in a week or two like this

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It is totally clean at this point. All rust, varnish, grease, oil and factory galvanizing is gone.

Now I realize I am very lucky to be able to have this done quickly and inexpensively so here is the GRM solution It is messy, kinda dangerous and inexpensive.

Go to Lowes Depot and purchase a gallon of muriatic acid

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Plug all holes with rubber, hose clamps, tape... whatever. Fill your tank 3/4 full with HOT water. Pour in the acid. Block off the filler neck and rotate the tank every ten minutes until you are positive that every square millimeter has been exposed to the solution for 20 or more minutes.

Pour out the rusty acid solution into a drum or large bucket and neutralize for safety. I used baking soda

Marvel that the innards of your tank went from this

 photo tankbefore.jpg

To this

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Note: there is no way I would ever do this again. It was a huge, stinky, skin burning mess. Neutralizing the acid kept foaming it up, my patio is still stained from it 8 years later. But it was under $10 If your tank is actually perforated and leaking fuel it will also be leaking the strong acid solution. It sucks, it is unnerving, your wife will hate you for it.

OK back to this Fiat tank today

now that it is clean we can see the issues

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Tools for this step are

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The liquid acid flux is only available via welding shops around here. It is critical. Flux pastes will not work. The solder is regular old lead free plumbing solder

Clean the area with a wire brush

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heat with the propane torch, dab some flux with an acid brush to clean, apply the heat again and start flowing the solder over the area

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File the high spots down (if you care to, totally unnecessary)

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And continue to the next area.

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It will be a mess of sticky burnt flux but that cleans off with a little solvent

When you have the tanks professionally dipped they have to drill a hole in them to ensure they get the air bubble out and the acid in. This one is 3/8" (they actually do this to the roofs of most cars too!)

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Popped a 7/16" plug with the press punch

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Soldered in place

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Whole tank cleaned up

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The reason I am soldering instead of welding is that fuel tanks are really, really thin. Some as thin as 24ga and to cut back far enough to get real metal to weld to I would most likely be remaking the entire bottom of this tank to fix that one corner. Brazing is another solution but the higher heat necessary will usually burn back the delicate lace of metal resulting in even larger gaps to try and seal.

The real star of this show is the tank sealant, which I ordered this morning. I usually use POR15 but I am really interested to try the Caswell product.

Next installment will be the cleaning and coating. Probably a week before the product arrives? Stay tuned, or don't. It is up to you.

AWSX1686 HalfDork
3/31/17 7:08 a.m.

Looks good!

I went over the tank on my e28 maybe 2 years ago when I thought it was leaking. I cleaned up the outside with a wire brush, then rust prevention spray pain, then bedliner on the outside, and POR15 tank liner on the inside. Turned out pretty well since I didn't actually have any holes.

My old motorcycle fuel tank was another story. It had some holes that would seep fuel, so I had my friend try to weld them and he ran into the issue with fuel tanks being thin, and the more he did, the more weak rust areas he uncovered. I ended up getting a used fuel tank on that one...

The0retical Dork
3/31/17 9:21 a.m.

Oh wow, I can't believe I missed this post. Thanks for posting I'll likely make an attempt to reproduce it depending on what I find.

I'm interested to see how the Caswell stuff worked for you. It's sitting on my workbench but I haven't had time to do much of anything with it.

Jumper K. Balls
Jumper K. Balls UberDork
4/16/17 12:59 p.m.

I will update this thread I have apparently forgotten about Monday with the sealing portion.

Jumper K. Balls
Jumper K. Balls UberDork
4/18/17 11:35 a.m.

Sorry about the delay.

So when we last checked in on our Fiat tank We had filled all visible pinholes and plugged the hole that the dippers had to make. The tank is clean and ready to go. The box from Caswell has arrived, you have read the directions, heated up the shop to the desired temp and are ready to go to work.

Get a roll of duct tape and start sealing off the sending unit hole and any other orifices. I use the little silicone plugs that come with powder coating kits for the smaller stuff and then tape over those.

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Mix up the epoxy.

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This stuff is thick and viscous. I am guessing around 30,000 centipoise but I no longer have a viscometer at my disposal.

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pour it in the filler neck.

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Yep it is in there alright.

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Then tape up the opening.

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For the next hour you will be turning the tank every which way. Letting it sit on all sides for 5 minutes or so. Tipping and turning to coat the insides with that thick goo.

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And after a while you will notice that it is coming out of holes you didn't see on first inspection.

When you think you have it everywhere it needs to be pull the tape off and pour out the excess.

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Now I found the catalyst in this to be ridiculously time sensitive. I had exactly one hour of working time. The sealant did not change in viscosity or gel up until an hour had passed and then the catalyst reacted, the tank came up to about 110 degrees and the stuff set up instantly. Within 10 minutes it was hard and dry. That made it more predictable than the POR-15 product I am used to which took a day to harden and 3 more to cure enough for fuel to be poured in.

From there the exterior needs to be painted.

That really is all there is to it.

AngryCorvair UltimaDork
4/18/17 4:06 p.m.

So where it comes out the pin holes you didn't know were there, does it seal those pin holes?

Jumper K. Balls
Jumper K. Balls UberDork
4/18/17 4:34 p.m.
AngryCorvair wrote: So where it comes out the pin holes you didn't know were there, does it seal those pin holes?

Yes. That is what it is designed to do and why it is so viscous.

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