Jumper K. Balls UberDork
Jan. 23, 2017 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

 photo tank1_zpsj1hxkhgh.jpg

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

 photo IMG_8156_zpska5skxxb.jpg

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

 photo tankstuff.jpg

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

 photo tankafter.jpg

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

 photo IMG_8158_zpslyrnpvcv.jpg

 photo IMG_8161_zpsi09gygjs.jpg

 photo IMG_8163_zps7ophpmcx.jpg

Tools for this step are

 photo IMG_8164_zpsr389rrws.jpg

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

 photo IMG_8166_zpsinfauegl.jpg

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

 photo IMG_8167_zpssnnnv9lc.jpg

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

 photo IMG_8168_zpsg1erxkym.jpg

And continue to the next area.

 photo IMG_8171_zpskc5wyqlu.jpg

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!)

 photo IMG_8172_zpstouo728h.jpg

Popped a 7/16" plug with the press punch

 photo IMG_8173_zpsdvymvf9g.jpg

Soldered in place

 photo IMG_8176_zpsitg9mlr1.jpg

Whole tank cleaned up

 photo IMG_8179_zpswshiy7mn.jpg

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
March 31, 2017 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...

March 31, 2017 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 UberDork
April 16, 2017 12:59 p.m.

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

Jumper K. Balls UberDork
April 18, 2017 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.

 photo sportscarshop121100_zpstmozrccf.jpg

Mix up the epoxy.

 photo sportscarshop123100_zpszep8fdtk.jpg

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

 photo sportscarshop125100_zps3kukfytb.jpg

pour it in the filler neck.

 photo sportscarshop126100_zps80f29z4k.jpg

Yep it is in there alright.

 photo sportscarshop127100_zpsrr15b9rr.jpg

Then tape up the opening.

 photo sportscarshop128100_zps1xwssgpm.jpg

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.

 photo sportscarshop130100_zpsql9qmsv4.jpg

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.

 photo sportscarshop131100_zpspoph6qja.jpg

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
April 18, 2017 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 UberDork
April 18, 2017 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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