Putting a drain plug in a gas tank?

[PeteVS]

How can I solder a "bung" for a drain plug to the bottom of a steel tank that's had gas in it? Fill it with water? That would make it difficult to solder. Fill it with CO2?

[marko39]

I have read co2 works but never tried it. I don’t think solder will be strong enough, would have to be welded. Got a spare tank you could practice on?

[tubman]

When we had to weld a steel gas tank back in my snowmobiling days, we'd empty it as much as we could and then took the hose from my mom's vacuum cleaner, shove one end up a car's exhaust pipe and put the other end in the tank. We'd go into the house and have a beer. Then we'd come out and weld away.

Just make sure the car you use isn't running rich.

[Kube]

Originally Posted by PeteVS

How can I solder a "bung" for a drain plug to the bottom of a steel tank that's had gas in it? Fill it with water? That would make it difficult to solder. Fill it with CO2?

Be very careful as ethanol-based fuels actually penetrate the steel. It is nearly impossible to weld these safely.
Note that most radiator shops will no longer repair tanks, something they used to do daily before ethanol came on the market.
Go ask an old-time radiator shop why that is...

[cas3]

Originally they were riveted and soldered while the inside was still accessible. Gonna be hard to duplicate that

[tommyleea]

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Originally Posted by marko39

I have read co2 works but never tried it. I don’t think solder will be strong enough, would have to be welded. Got a spare tank you could practice on?

CO2 seems like it would be safe, but I was going to use it to static leak test my A/C in my car, and was told it would be very dangerous, might explode? Still don't understand it. Used Nitrogen.

[Jack E/NJ]

Why?

[highbeams]

That thought needs to go south . . . . .

[Robert/Texas]

When I in the army, stationed near Kaiserslautern, Germany in 1958, I had a 1950 Mercedes 170-S. Four of us had the weekend off so we decided to drive to Paris and spend the night there. We reached Saarbrucken and the engine started missing out. We stopped at a Mercedes dealer and they found leaves in the gas tank. They tried to vacuum them all out. Some miles later the engine began missing again in a small town in France so we stopped in a small auto repair shop. One guy with us spoke some French and told the mechanic about our problem. I didn't see how he drained the gas but when he had the car up on the his lift he cut a large hole in the gas tank with a drill and hacksaw and got the rest of the leaves out. Then he gas welded the piece back in and replaced the gas through a filter. We made it to Paris and back and we had a great time but that's another story.

[Kube]

Originally Posted by Robert/Texas

When I in the army, stationed near Kaiserslautern, Germany in 1958, I had a 1950 Mercedes 180-S. Four of us had the weekend off so we decided to drive to Paris and spend the night there. We reached Saarbrucken and the engine started missing out. We stopped at a Mercedes dealer and they found leaves in the gas tank. They tried to vacuum them all out. Some miles later the engine began missing again in a small town in France so we stopped in a small auto repair shop. One guy with us spoke some French and told the mechanic about our problem. I didn't see how he drained the gas but when he had the car up on the his lift he cut a large hole in the gas tank with a drill and hacksaw and got the rest of the leaves out. Then he gas welded the piece back in and replaced the gas through a filter. We made it to Paris and back and we had a great time but that's another story.

That was pre ethanol..

[Flathead Fever]

At the phone company the Vender that installed the racks in the back of the vans used parolees, they drilled through the floors, and it never occurred to them there were gas tanks under there. They drilled right into them. They did it to hundreds of brand new Dodge vans. It wasn't discovered until the vans had been delivered all over CA. They sent out a guy to each location. he dropped drop the "full" tanks down far enough that he could weld up the holes. He had flow meter like an a TIG welder, hooked to either nitrogen or Co2 to purge the oxygen out of the tanks. He welded those tanks with gas in them and he didn't blowup.

No matter how clean you think the metal is, the fuel can get into the metal. The heat can bring the fuel out of the metal and turn it into vapor that can ignite. Unless there is zero oxygen in the tank. It doesn't seem worth it to me just to have a drain plug when you can take an electric pump and suck the fuel out or siphon it.

[Jack E/NJ]

If you just wanna gotta have a gasoline tank drain plug, use a gasketted pipe flange affixed with sheet metal screws. A big one if you want to fish out tree leaves & branches, dead mice, rocks, slime mold and plain slop that are commonly found in old Ford tanks.

[Clem Clement]

N2 might be ok. I have used a goo to seal the tank.
Here is what not to do: I bought a 54 Merc that had a gas leak. Turned out the former owner has stuffed a bath towel in over the tank to reduce rattling. I dropped the tank and flushed it in the street in front of his gas station. 3 times the left the tank in the so
un over lunch (Lemon Butter with my aunt.) Then he dropped a match in the tank. The tank did a dance and we soldered coffee can sheets and good to go.

Never use a vacuum in a gas tank if the gas

can has liquid gas in it. fumes and motor spart5s=boom

[tommyleea]

Originally Posted by tommyleea

CO2 seems like it would be safe, but I was going to use it to static leak test my A/C in my car, and was told it would be very dangerous, might explode? Still don't understand it. Used Nitrogen.

My bad..I was going to use oxygen not Co2..Sorry..

[Bill OH]

I blew air into a 23 gallon gas tank thru the fill opening with my shop vac discharge for about 20 minutes and then welded the tank with shop vac running during the welding. On the other hand I washed out a small engine tank with hot water and it went woof when I passed a propane torch over the fill.

[Brian]

it went woof when I passed a propane torch over the fill....
so does my dog!!

[jplutz]

Greetings from a new guy!! I bought my 52 last year and found out that the gas tank was leaking at the drain plug. Previous owners had tried to fix it with RTV's of various types and the plug was stripped. There was no gasket and no part #'s for the plug. A guy at NAPA suggested the following which he ordered for me and which sealed the Bung hole perfectly: A neoprene plug, which is impervious to ALL gasoline types. The hole is 7/8" wide, the plug is 7/8" wide c 1 1 /2" thick, with a bolt threw the center and washers on both sides and a nut on bottom. I fit the plug in the hole and tightened the nut carefully. The neoprene expanded as the washers crushed it and sealed the hole. No welding!! No heat!
NAPA has various size neoprene plugs that can do this for you. All's ya gotta do is drill a hole.

Hope this helps. JPL

[Lawson Cox]

How do you get this sort of plug INSIDE the gas tank, and with a wrench?

[GB SISSON]

I have made these for various situations. It's like the old thermos plug with a lever on top. I use a carraige bolt with a head same dia as rubber plug. It can have a washer under the head if wanted. Then a nut and washer on the outside of tank. If all is a relatively tight fit, the head never seems to spin on the inside. I have not done this with the neoprene in a fuel tank, but with cooling systems and the drain plug in the transom of my old boat. I cannot recall ever seeing sparks when drilling steel with a hole saw. Perhaps someone here has. If so, use all the precautions as though you were welding.

[blucar]

I could not begin to tell you how many gas tanks i have repaired and/or built during the past sixty plus years. In the early days of RV'ing I built many AUX fuel tanks for my RV and several friends.
In the mid 1960's when I was building fuel tanks wire-feed welders were not very common, electric welders were not much good on light steel so I used my Victor OXY Acetylene torch that i used fro body repair work.
I would have the local steel supply shop shear and bend the 16 gauge to my specified size then I wold gas weld the remaining seams Once the tank was finished I would hook up a tire pump to the tank, filling it with with a few ponds of air and spay liquid soap/Windex on the welded seams to check for leaks.
Having lived in rural Idaho in my youth and working in several repair shops, repairing rock damaged fuel tanks was almost an every day affair.
We would drain the fuel, remove the tank, flush it with water, then wave a gas torch over the open fuel filler neck, if there was any fumes left in the tank they would burn off with a light quick burn-off of the fumes.
Soldering the tank with an Oxy torch was very simple once the metal was cleaned and 'tinned'.. I said Oxy torch because propane torch's had not been invented yet in the 1950'-60's. The closest thing to a propane torch was a white gas blow torch and a soldering iron that was heated by the blow torch. Hmmmmm, still have one of those in my garage collecting dust.
Actually, IVORY Soap is a very good semi perminent gas tank repair.