How to build a gas tank from scratch- Save Money and replace that Rusty Tank!

I have an affinity for old barn-find type vehicles and I live for bringing them back from the dead. Over the passed few years I’ve been shopping for a “swap-meet truck” that I could use to buy or sell out of at the local swap meets. I mean come on, what would be cooler than rolling up to buy some old rusty car parts than in a cool old truck?!! I came across this 1942 Ford Flathead V8 box truck a couple years ago when a friend bought it and I’ve been after him for a while now to buy it. This winter the chance came and before I knew it one of my other classic vehicles was sold and this replaced it.

Now that we’re thawing out here in Eastwood country I’ve decided to get this old gal back on the road and I decided to tackle the mechanics. The problem with any “barn find” like this is that they normally have mechanically deteriorated just from sitting for so long. Normally people don’t plan to park a vehicle for a long time, just until they get time to fix it up. This means all of the fluids are left in the vehicle and those fluids over time tend to break down and cause issues. The worst thing to do if you park a vehicle for a long period of time (more than 6-8 months in my opinion) is to leave fuel in the tank. Over time the fuel breaks down and turns back into it’s original fossilized state. The temperature changes and the gas in the tank also promotes corrosion over time and the tank eventually rots out.

While our gas tank restoration kits are pretty amazing and can bring some pretty nasty fuel tanks back to life, there’s times where they’re just too far gone and you’r going to be chasing issues for the life of the car. In most cases I’d advise to just replace the tank with a reproduction tank, but when you’re working with oddball stuff or on a tight budget it isn’t always possible.

When I pulled the fuel feed line and the tank from the “meat truck” I knew I was in trouble. The outlet of the tank and the hardline were both blocked with solidified fuel. Once I dropped the tank and peeked inside with one of our LED penlights I saw there was about 5-6 gallons of fuel in the tank and a LOT of debris in the bottom of the tank. I’m talking sheets of rust and solidified fuel!

I started pricing out “universal” gas tanks and none of them were the right size/shape and they were all $300-$400 and up. Tough to swallow when I’d still have to modify a lot of stuff under the truck to make one fit and work! After reading a few threads on the H.A.M.B. about guys who had tackled smaller scratch-built tank projects I decided to take on the project myself.

For this fuel tank the shape of the entire tank is really based off of the end caps, so in my case I cut one off of the original tank and used it as a pattern. I traced out the shape of the end cap on a piece of 18 gauge steel, leaving extra material for a flange. I then used the 1/2″ diameter T-dolly from the 5 piece T-dolly kit and hammered the edges over to create a flange on each endcap.

Once I had the end caps shaped I wanted to assure that they didn’t stretch or oil can too much from the weight and sloshing of the fuel in the tank. I strayed from the original tank a little and used the 1/8″ dies in the bead roller to roll an X-shape pattern into each end for strength (it also looks pretty cool!).

Next I cut out a large piece of 18 gauge that matched the size I need to wrap around the end caps. I measured with a tape measure and also used a thin piece of scrap steel to wrap around one of the end caps to assure that I had the correct size needed overall. I added a little extra where it overlapped so I could lap weld the tank at the main seam. I then marked out and rolled 1/8″ beads in the panel that would keep the tank from oil canning when full of fuel. I stopped the beads a little short so that I could have a flat lap weld down the center seam.

When laying out the lines for the bead roller I also marked out my approximate bend lines on the tank body. Because this tank is so long I wasn’t going to be able to just hand form the shape over the entire piece by just using the end caps like I’ve seen others do. I also didn’t have a large metal brake handy so I took some 1/4″ thick angle and clamped it down on the table with some locking welding clamps over the sheet metal and bent the metal over the edge of the welding table using some good old fashioned brute force. I moved the piece a little at a time checking fitment to the end caps and bent the next profile the same way until I had my box shape. I did use a nylon mallet on the first bend but I found it made the edge too wavy and caused too much distortion/finish work (you can see it on the edges in some pics later in the assembly of the tank) so I opted for using my body weight to bend the panel more evenly for the rest of the bends.

I then got some extra hands to help hold the first end cap in place and press the sheet metal tightly against the 1/2″ flange I had made. I tack welded every few inches with the MIG 175 until this first end was tightly held in place. Once we got towards the main tank seam I used a ratchet strap to help pull the seam and shape of the tank together. This may not be necessary for a smaller tank, but this tank was so long we needed any help we could get! With the tank taking shape I took the tank back home to test fitment in the truck and finish building it to the original tank. I first confirmed the fuel filler neck would hit where it needed to in the floor board of the truck.

The original tank also had two divider baffles in it that had the corners notched out. These are to reduce the sloshing in the tank and potential fuel delivery issues when the tank gets lower in fuel. I decided to replicate the placement of the baffles and add some additional flared holes for strength and to allow quicker filling of the tank. I first rough cut the shape of the dividers with the throatless shear and then used the hole saw kit to drill a 1.5″ hole in the 18 gauge baffles. I didn’t have the appropriate sized punch-flare tool handy so I used an old trick to get the same effect. I placed the metal over an old large socket I had clamped in the vice and I placed the tapered end of a nylon teardrop hammer in the hole and struck it with a flat nylon hammer to flare the hole and in return strengthen the panel. This method is great if you don’t have a punch/flare tool on hand, but it’s difficult to get the a consistent flare on each hole. In this case these parts would be hidden inside the tank, so strength was my only concern.

I then cut the baffles a little small and cut the corners off so that there was plenty of room for fuel to pass bay the baffles even when the tank was very low on fuel. I used the MIG 175 to spot weld the baffles in place so they wouldn’t move from the force of the fuel trying to slosh around.

With the baffles in place I moved my ratchet strap all the way to the other open end and begin tightening it down until the metal pulled around the last end cap so I could spot weld it in place. Before I fully welded the end caps in place I clamped and pulled the center seam together and tack welded it every few inches to keep it from moving around. I then used the TIG 200 AC/DC and fully seam welded the end caps in place. I would weld every few inches and then hammer the metal for the next portion down tight with the body hammer when the metal was still hot. This pulled the metal together and gave me a nice seam to weld. I then welded the entire center seam again working slowly and making sure the seam stayed tightly clamped together as I welded. I did get a little warpage on this center seam, but nothing that would be an issue (and would be hidden when mounted. If this was an exposed tank I would have used a resistance stud welder or the MIG stud kit to pull the low spots up and make the tank closer to perfect, but not needed for this old workhorse!

To save some money and time I cut out the fuel filler neck, fuel sending unit mount, and the fuel drain port and welded them into the new tank so I could utilize the original fittings, fuel sender, and mounts. This did take some extra time in the end as some of the parts were leaded in place and I had to burn the lead out with a torch after cutting them after of the original tank before I welded. In the end though it made fitting the new tank a breeze and I’d say it was worth that small hassle.

I then filled the tank with water and let it sit overnight, making notes of any small leaks I had missed. Luckily there were only 2 very small spots that were weeping after sitting and were quickly filled with small dabs of weld. I then drained the tank out and cleaned it thoroughly before sealing the inside with our gas tank sealer kit so this tank could outlast myself and potentially the truck! I then top coated the outside of the tank with a few coats textured rust encapsulator and set it next to the old carcass of a fuel tank. The overall shape and size ended up being VERY close and only took me installing slightly longer bolts in the tanks straps to make installation easier (my tank has more rounded corners and was difficult to get the original bolts started).

I finally cleared the fuel feed line with Aerosol Injected Cleaner and installed the line and the sender wiring. I added 5 gallons of fuel and filled the fuel filter glass bowl with fuel before turning the truck over. After 2-3 cranks the old Ford flathead V8 fired right up and sounded pretty darn good! I’m happy to report the tank seams to be leak free and has allowed me to successfully move the truck around my driveway, which is probably the first time it has moved under its own power since the early 1960’s! In end the supplies to build this tank would be under $100 and the extra money saved can now be put into restoring the brake system other mechanical components. Hopefully I can get her back on the road just in time for the spring swap meet season to start!

-Matt/EW