Have you ever welded or bonded a sump to fuel tank?

[Truckedup]

I weld ,braze or soldier motorcycle tanks ....They are smaller and easier to handle but I flush it with acetone or lacquer thinner, then drain it out...Shop vac on blow for about 1/2 hour...Then a flush with alcohol and more shop vac action...I don't believe in filling tanks with water because any remaining fumes will be compressed and more like to ignite with force..If you're in a hurry, inert gas filling is the best approach...

[rebelrouser]

Oxy welded several, sumps in gas tanks. The old dog way I was taught was to drain the tank, then hook up a hose to car exhaust, run the car for a few hours, the engine exhaust will displace the gas fumes. Of course you have to use a car with an engine running well with no issues. And tank has to have enough openings to have a flow through the tank. Used it a couple times and worked like a charm.

[Dan Timberlake]

I love epoxy, but would not trust it on a "structural" modification without mechanical fastening back up.
A general rule for aircraft composite structures is that additions to a (one piece) "primary structure" must use mechanical fastening in addition to bonding.
I picture a gas tank sump is going get whacked once in a while, like just being slapped by running over a piece of truck tread.

Steel typically has 10% or more elongation before failure which is just what I need to protect me from myself.

One piece Integrally molded Composite parts have virtually no elongation, and epoxy bonded joints are worse. Immense bond areas can be pretty strong,
Lesser resins, like polyester "fiberglass" resins are mighty weak, and shrink a bunch while curing, so use up a lot of their bond strength just hanging on to the primary structure.

[55chev]

Oxy welded several, sumps in gas tanks. The old dog way I was taught was to drain the tank, then hook up a hose to car exhaust, run the car for a few hours, the engine exhaust will displace the gas fumes. Of course you have to use a car with an engine running well with no issues. And tank has to have enough openings to have a flow through the tank. Used it a couple times and worked like a charm.

this works very well..

[Dave Koehler]

The epoxy is a bad idea. I am more concerned with your dangerous welding concern.
What process did you intend to weld with?
If you have no welding skills, just go hire a pro and save us some worry.

[peejay]

I have brazed.

Empty the tank, connect a garden hose to your water heater and set the thermostat to Chernobyl, then when the water is up to temp, fill the tank to overflowing. Gasoline evaporates at 150F, so get the water hotter than that and it WILL remove the leftover fuel, even the fuel embedded in the metal's pores. Proof that you got it all is when there is no more oil sheen on the top of the water. Do not use soap or detergent, that allows the water and oil to mix and that is the opposite of what you want!

I then drain the water out and work on a dry tank.

Ain't exploded yet.

[Dirtybob]

We do a lot of underground storage tank (gas/diesel) replacements at work, 800 to 10,000+ gallons. State requires the tanks have holes cut in them and certified clean before going to scrap. Typical procedure is to inert with nitrogen but I have seen some industrial vacuums work well too. Think of a shop vac, mounted on a 55 gallon drum, powered by an air compressor. Will inert a 5k gallon tank in short order. I would think a shop vac could achieve similar results (on a smaller tank).

[econo racer]

I would only weld on a new tank now after what all has been said. I don't want any rust in the fuel what so ever. Can I drill a hole at the lowest point and install a fitting with threads and some type of crush washer? I might just use the tank as is new.

[enigma57]

Oxy welded several, sumps in gas tanks. The old dog way I was taught was to drain the tank, then hook up a hose to car exhaust, run the car for a few hours, the engine exhaust will displace the gas fumes. Of course you have to use a car with an engine running well with no issues. And tank has to have enough openings to have a flow through the tank. Used it a couple times and worked like a charm.

That's exactly right! I've done several this way many moons ago. Very important to flush tank, empty it and allow to dry thoroughly before beginning and to purge at least 15 minutes before beginning. I ran an old radiator hose over a tailpipe and attached the other end to the filler tube on the tank. Also important to have cross ventilation. I removed the fuel pickup and gauge sending unit and allowed the exhaust to exit there.

Also set idle up a bit. At least 1,500 RPMs or higher. If you have a hot cam, you want revs high enough to ensure no unburnt fumes remain in tank.

DON'T PLAY RUSSIAN ROULETTE! KEEP THE PURGE GOING ALL THE WHILE YOU ARE WELDING OR BRAZING! Metal is porous and explosive residue of gases can be trapped in those pores for extended periods of time. Even metal tanks and drums that have been meticulously cleaned priour to welding and/or have been drained and allowed to dry for long periods of time priour to welding or cutting operations have on occasion exploded when hot work was initiated.

Filling the tank with water and attempting to braze it, gas weld it or TIG it as some have suggested...... I cannot imagine. If anyone here has ever tried that, they will understand why I say this. You cannot bring the base metal up to brazing nor welding temps if water is in contact with and cooling the thin base metal from the back side.

After welding was completed, I coated the inside of my tanks with a product designed for coating fuel tanks of boats. After this had dried and cured for some days, I installed the fuel pickup and gauge sending unit and installed the tank.

Best regards and don't blow yourself up,

Harry

[enigma57]

I would only weld on a new tank now after what all has been said. I don't want any rust in the fuel what so ever. Can I drill a hole at the lowest point and install a fitting with threads and some type of crush washer? I might just use the tank as is new.

You could use a bulkhead fitting and do that. You would need to be able to tighten part of this from inside the tank. That would likely require reaching in through the hole your fuel pickup and gauge sending unit are bolted to. My hands and arms are too large to get in there through the smallish holes most vintage American cars are provided with.

On the other hand, my wife had a 2003 Nissan Maxima a while back and it had an electric fuel pump in the tank and the fuel pickup and gauge sending unit were all a part of the one assembly. I replaced the pump and it had a nice large hole where it bolted to the top of the tank. Was also fortunate, as the Maxima had a cover plate under the rear seat cushion which could be removed to perform this work. So I did not have to drain and remove the tank.

Here is a brass bulkhead fitting as an example. You can probably find smaller ones in brass or stainless steel. And make sure you use gasket seals that are viton or other gasoline resistant material......

Edit...... The website here will not permit the link I posted to be seen for some reason. Cut, paste and Google this and you will see them......

Joywayus 3/8" Female 1/2" Male Solid Brass Water Tank Connector Threaded Bulkhead Fitting

Good luck with your tank mods,

Harry

[turbo camino]

The new Spectra tanks are already pre-tinned for you inside and out with tin/lead - it is solder! For rust protection! To weld it, you have to grind that off on the outside and on the inside it ends up burned away leaving crusty non-coated steel. It will rust. Why not just solder to the pre-tinned tank? Just pretend it's a radiator.

https://www.rockauto.com/en/moreinfo.php?pk=17563

I'm not sure the wagon tank would benefit from a sump anyhow, it's fairly tall and skinny compared to the other G-body tanks, the fuel doesn't have much of anywhere to go other than close to wherever you put the outlet fitting. The issue with adding a bulkhead fitting in the bottom is the sender opening is too small to fit your arm in there to hold the backup nut for the fitting. Soldering a flanged bung to the exterior is a much cleaner solution.

[Schurkey]

I hauled a tank and a sump to the local radiator repair shop. He riveted the sump to the tank, then sealed it with solder. He told me afterward that he had some trouble getting the solder to stick--but it's been holding for decades.

[Tuner]

I've oxy-acetylene torch welded and brazed tanks with exhaust from a running engine piped into them. Watched my father do it that way when I was a kid and never had or seen a problem doing it that way. I have seen three tanks explode when filled with water and had water running into and out of them from a garden hose.

The danger of filling a tank with water is the maximum flame temperature for oxy-acetylene is approximately 3,160°C and at 3000 °C more than 50% of the water molecules are decomposed. Think Hindenburg.

[stealth]

I’d never risk it for the price of a new tank...

Look into Holley hydramat if you need to use special tank