Welding up a new tank

jake

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I am making a fuel tank out of stainless as I plan on putting in a fuel pump for a holley sniper system(more to come on that, 383 stroked). If I can not get my hands on enough ss, I plan on using 16 gauge carbon steel which I have unlimited access to. I am a welder by trade so I am not worried about leaks, but curious about rust. My existing original fuel tank is out of the car and looks absolutely perfect on the inside, no rust at all but I keep reading about sealers in fab forums. My thought is that the original did not have it so my new one will not either. What do you guys think? Anyone else done this before? I have a idea on a baffle design but any ideas would be wonderful. The tank is going to match oem except 1 inch deeper and have a flat step on the top in the front to mount the fuel pump.
Side view
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I'd avoid sealer personally. If you keep the tank full of fuel they don't rust or if you keep the car in a climate controlled environment where they can't condense water in the tank they don't rust either. Its leaving them empty or low and letting water condense that kills tanks.
I've heard that sealers can come loose and plug filters and lines sometimes. They say with good old fashioned gas that is not much of a problem but with the new "blended" fuels it is. Don't know personally about that claim but with the damage the fuel does to other things I would not be surprised.
 
The factory tanks used to have some sort of galvanize coating on them. The GM tanks had something like "Long Tern" stamped on them. Not sure if that was a treatment or a type of material they were stamped out of.

The issue with sealers not adhering properly was usually on rusty tanks that were not professionally cleaned before their (usually DIY) application.

The isssue with current ethanol'd fuels is that ethanol, being a member of the alcohol family, attracts water from the air. The resultant gunk sinks to the bottom of the tank as "phase separation".

The reason that many people with pickup trucks went with fiberglass fuel tanks, when gas was really GAS, was to get away from the rust issues of the custom-made steel tanks they'd been using previously. Probably similar for the boat people who also had fiberglass fuel tanks. But all of that ended with ethanol, as it degraded and "melted" the fiberglass tanks, which had to be replaced before any engine damage resulted.

Find some way to "pickle" your new steel tank to keep the rust away. BEFORE any fuel is put into it.

As for baffles, find a fuel tank from a '87-'92 GM pickup or Suburban. Below the hole where the sending unit goes in, you'll see a round plastic baffle. What locates the baffle is a u-shaped strap that is tacked to the bottom of the tank. The two dowels stick up through the baffle, retained by special-coated speed nuts. Get the baffle, speed nuts, and you can probably fab somthing similar to the strap that is tacked onto the tank's floor.

Initially, they only used one speed nut to retain the baffle, but after about 12K miles, the baffle would get loose and (with the force of the moving fuel) wreck the fuel pump unit. The fix? Put the second specially-coated speed nut on the other dowel.

We were told they were specially coated to not rust. They looked just like any other speed niut in our hardware parts selection, but we never had any issues with rust clogging fuel filters either.

Just some thoughts and recollections,
CBODY67
 
I see no clear advantage to using stainless steel. Id certainly have a shop with a brake, bend up as much of that tank as possible. If your TIG welding and have butt welds, that presents another problem as you have to back purge.
Myself id think about aluminum instead.
 
I am making a fuel tank out of stainless as I plan on putting in a fuel pump for a holley sniper system(more to come on that, 383 stroked). If I can not get my hands on enough ss, I plan on using 16 gauge carbon steel which I have unlimited access to. I am a welder by trade so I am not worried about leaks, but curious about rust. My existing original fuel tank is out of the car and looks absolutely perfect on the inside, no rust at all but I keep reading about sealers in fab forums. My thought is that the original did not have it so my new one will not either. What do you guys think? Anyone else done this before? I have a idea on a baffle design but any ideas would be wonderful. The tank is going to match oem except 1 inch deeper and have a flat step on the top in the front to mount the fuel pump.
Side view

I'm pretty sure that gas tanks are nickel plated steel, not galvanized. Hot dip galvanize might cause an internal problem in the tank as the zinc breaks down, but I'm not really sure on that. However, wet road salt would corrode hot dip galvanized steel pretty quickly.

Sealers? All claim to work and some seem to work, but the ethanol laced fuels seem to be tough on all of them. I always wonder if it's more about prep that causes the failures rather than the sealers. Usually the guys that ***** the loudest about something not working are the ones that don't follow the directions. You would have an advantage of being able to clean and prep the internal surface before assembly, but it could still be a crap shoot.

I got curious (and a little bored while I wait for the morning pain meds to "kick in") and found a couple videos on how they make gas tanks. I think they call the machine that welds the flange together a "seam welder" (makes sense, right?). Note the difference in manufacturing between the two. A lot of automation for Spectra (wasn't that a James Bond villain?) and the Asian company would cause an OSHA inspector to have a stroke. Not even safety glasses!



 
Perhaps my reference to "galvanize" was incorrect, but I know there was some sort of coating on the tank's external metal. I soon learned to get a shop towel to put between my hands and the tanks so that I didn't end up with a blackish oily-ish residue on my hands. Had to be very careful as the OEM seam welds and the seam edges were very sharp! Those were mid-to-late '70s OEM GM fuel tanks.

Thanks for the videos!
CBODY67
 
Perhaps my reference to "galvanize" was incorrect, but I know there was some sort of coating on the tank's external metal. I soon learned to get a shop towel to put between my hands and the tanks so that I didn't end up with a blackish oily-ish residue on my hands. Had to be very careful as the OEM seam welds and the seam edges were very sharp! Those were mid-to-late '70s OEM GM fuel tanks.

Thanks for the videos!
CBODY67
That oil might have been something to keep the rust to a minimum. From what I've seen with the way new gas tanks are handled, they get piled on and dragged across everything and the thin plating (you know it's thin) gets scratched and then it rusts. A customer is going to say "no thanks" to a pre-rusted gas tank. LOL.

They don't do a deburr type secondary operation with the tanks. Most are probably just headed to be installed in new cars, so handling amounts to loading and unloading a pallet full and then stuffing it under a car on the assembly line. That deburr would probably add a buck or three to the cost.
 
There is an epoxy liner called Caswells that works very well. I have had it in my motorcycle tank for over 10 years. If your building a tank you need to have a plan for testing. My motorcylce tank has over 12 ft of weld joint. At no more than an inch at a time that's 150 tie ins. With a sheetmetal tank you cant pressurize them to to an effective amount without creating a bomb.
My tank would hold 2-3 lbs for weeks. I ended up doing a submersion test. Which is also very difficult. They want to float. I had a few leaks that would take 30 minutes to form a bubble the size of a pin head. I thought my eyes were off.
I was a pipe welder for years. Proficient in all manual processes on many materials. But it is just not comparable to one passing and hammering and sanding sheetmetal.
If I was to do a car tank I would probably do aluminum of a substantial gauge and outside corner joints.
 
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