# full gas tank welding **URL:** \ **Category:** Factual Questions\ **Created:** [August 22, 2000, 12:12am UTC](https://boards.straightdope.com/t/full-gas-tank-welding/30239 "2000-08-22T00:12:43Z")\ **Posts on this page:** 9\ **Page:** 2
**Author:** ![DougC](https://avatars.discourse-cdn.com/v4/letter/d/7feea3/32.png) [@DougC](https://boards.straightdope.com/u/DougC)\ **Post date:** [August 23, 2000, 12:04am UTC](https://boards.straightdope.com/t/full-gas-tank-welding/30239/21 "2000-08-23T00:04:59Z")
- - - To ignite gasoline vapors you need to have a spark; a smoldering piece of material won’t do it, ever. The danger of allowing smoking around gas pumps is that somebody will get out a new cig and try to light it, not that any cigarette already lit will do anything. - Also I have only heard of the welding-the-gas-tank thing for antique or otherwise unavailable replacements. - MC ---
**Author:** ![DennisKy](https://avatars.discourse-cdn.com/v4/letter/d/58f4c7/32.png) [@DennisKy](https://boards.straightdope.com/u/DennisKy)\ **Post date:** [August 23, 2000, 12:56am UTC](https://boards.straightdope.com/t/full-gas-tank-welding/30239/22 "2000-08-23T00:56:39Z")
The way I was told by a welder to do something like this was as previously described, except instead of using exhaust gas, you stick the business end of a CO2 extinguisher into the filler and let fly for several seconds until the tank is good and cold, lined with dry ice, and filled only with C02 gas. ---
**Author:** ![warmgun](https://avatars.discourse-cdn.com/v4/letter/w/ecccb3/32.png) [@warmgun](https://boards.straightdope.com/u/warmgun)\ **Post date:** [August 23, 2000, 1:59am UTC](https://boards.straightdope.com/t/full-gas-tank-welding/30239/23 "2000-08-23T01:59:39Z")
Gotta disagree with ya, MC. I saw a fire hazard demostration put on by the fire dept. once. They exploded gasoline fumes with a cigarette quite effectively. ---
**Author:** ![mangeorge](https://avatars.discourse-cdn.com/v4/letter/m/d78d45/32.png) [@mangeorge](https://boards.straightdope.com/u/mangeorge)\ **Post date:** [August 23, 2000, 1:59am UTC](https://boards.straightdope.com/t/full-gas-tank-welding/30239/24 "2000-08-23T01:59:42Z")
> [@](#): > > \*Originally posted by mangeorge \* > \*\*You guts are freakin’ CRAZY! 😃 > Peace, > mangeorge \*\* I think that what mangeorge means is “You _guys_ are freakin’ crazy.” He’s right. Peace, The Phantom Editor ---
**Author:** ![Yeah](https://avatars.discourse-cdn.com/v4/letter/y/dbc845/32.png) [@Yeah](https://boards.straightdope.com/u/Yeah)\ **Post date:** [August 23, 2000, 2:44am UTC](https://boards.straightdope.com/t/full-gas-tank-welding/30239/25 "2000-08-23T02:44:55Z")
Instead of filling the rinsed-out gas tank with exhaust fumes, you can, in theory, toss in a chunk of dry ice and let it displace any oxygen before you weld or solder (but you have to be careful that you don’t accidentally pour out the carbon dioxide before you finish welding/soldering). The many anecdotes are amusing and cautionary but not quite so informative as one might desire. Don’t any welders or motorcycle mechanics/enthusiasts read this board? ---
**Author:** ![Satan](https://avatars.discourse-cdn.com/v4/letter/s/e9bcb4/32.png) [@Satan](https://boards.straightdope.com/u/Satan)\ **Post date:** [August 23, 2000, 3:40am UTC](https://boards.straightdope.com/t/full-gas-tank-welding/30239/26 "2000-08-23T03:40:53Z")
> [@](#): > > \*Originally posted by Homer \* > **My uncle was changing his oil while smoking once, and I was like, uh… that’s pretty dumb, Tim (I’m named after him) and he took his smoke out and dipped it in the oil and said "A cigarette’s not hot enough to catch up oil."** Just to clear this up, motor oil is not flammable at all. Its job is to lubricate an engine where friction will cause temperatures FAR in excess of a cigarette just within a couple of seconds of firing it up. In fact, evebn gas is not as flamable as you would think. One day I smelled strong gas odor coming from under the hood of my car. I didn’t do anything about it until my light rthat said I was overheating came on. I stopped the car, opened the hood while it was running, and saw gas spewing all over my engine, and it was smoking and sputtering! The :eek: smilie does not do my reaction justice… Despite this, it never caught flame because you need an actual spark to get it going. Of course, something like a faulty spark plug would have been enough to cause that spark, but it goes to show that if an overheating engine won’t blow up gas that is literally spewing over it, it ain’t quite as bad as people think. * * * Yer pal, Satan [sub]TIME ELAPSED SINCE I QUIT SMOKING: Four months, two weeks, 1 hour, 35 minutes and 49 seconds. 5442 cigarettes not smoked, saving $680.33. Life saved: 2 weeks, 4 days, 21 hours, 30 minutes.[/sub] **_"Satan is not an unattractive person."_-Drain Bead** [sub]Thanks for the ringing endorsement, honey!\*[/sub] ---
**Author:** ![dp](https://avatars.discourse-cdn.com/v4/letter/d/ecd19e/32.png) [@dp](https://boards.straightdope.com/u/dp)\ **Post date:** [August 23, 2000, 3:57am UTC](https://boards.straightdope.com/t/full-gas-tank-welding/30239/27 "2000-08-23T03:57:05Z")
I have used a product similar to JB Weld to patch gas tanks. It is available at auto parts stores. You don’t have to take the tank off, or drain it. Just put it over the hole. It has worked fine for me in the past. I cannot remember the name of the product or the mfg. Just ask the counterman for some gas tank patch. ---
**Author:** ![Quinn1](https://avatars.discourse-cdn.com/v4/letter/q/6de8d8/32.png) [@Quinn1](https://boards.straightdope.com/u/Quinn1)\ **Post date:** [June 13, 2025, 11:29am UTC](https://boards.straightdope.com/t/full-gas-tank-welding/30239/28 "2025-06-13T11:29:24Z")
When I was stationed in Germany in the Army my gas tank on my car needed to be welded. Well back home in welding school my instructor a very experienced person taught me that if you need to weld a fuel tank in the field then fill it completely up all the way then weld it. So I filled my tank completely with fuel crawled under it with a torch and brazed it welded it up as the company welder stood by watching me. I did it myself repaired the tank no problem. I will never forget that memory. ---
**Author:** ![Retzbu\_Tox](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/retzbu_tox/32/11829_2.png) [@Retzbu\_Tox](https://boards.straightdope.com/u/Retzbu_Tox)\ **Post date:** [June 13, 2025, 5:33pm UTC](https://boards.straightdope.com/t/full-gas-tank-welding/30239/29 "2025-06-13T17:33:13Z")
My dad was a mechanic for the majority of his adult life, and I think brazing was his preferred method for patching a hole in a gas tank, as long as the tank was absolutely full of fuel (no air). Everyone else would clear out of the shop during the process. If he had to patch one that had air in it, he would solder it. I still have the humongous soldering iron he would use. [Previous page](https://boards.straightdope.com/t/full-gas-tank-welding/30239.md?page=1)