Welding oil pan.

I need to repair a pinhole on a steel oil pan. I would like to drain the oil and clean it up. And weld. If I put argon into the engine would that keep the oil from catching fire in the pan? 

I would remove the pan, you need to clean the backside as well. The argon may work, but no way to be sure.

Take the valve covers off and weld away.  That way, when the fumes in the pan explode, the forces will go up, and you won't be killed, just badly burned.

How about soldering it?  Might be tough with oil on the backside, but you won't know till you try.

Just went through this with a Cummins ISX at work.  Customer didn't want to pay the time to remove it.  Ended up paying for the time to drain, clean, weld, test, drain again, remove the pan and do it all again.     You won't get it clean enough to weld from the outside unless you get really lucky.  If you don't want to remove it, just clean it with a bunch of brake clean, wire brush, and JBweld it until you can do it right. 

Just my 2 cents

Yeah, I think JBWeld/epoxy is the right answer if the pan is staying on the car.

Oil will contaminate the weld if you don't take it off and clean the inside of the pan as well...there is no question on this. As for whether you could weld with the pan on the car without it blowing up? Sure...its a pinhole, if the pan is full of oil, the oil will dissipate the heat from the small weld needed long before it becomes dangerous...explosions don't happen without oxygen and accelerant in the proper ratio....there is no air on the other side if the pan is full of oil....and the "accelerant" (in this case oil) on the outside of the pan isn't in the air at all....you could possibly light some surface oil on fire, but thats about all that will happen....but its a moot question....since the weld will be contaminated anyway.

P.S. JB Weld wont work for long either...it never does when in contact with oil in my experience....some peple have had better luck, but when it comes to oil, J.B. Weld is a strictly short term solution.

You could weld a "patch" over the outside of the hole.  That way you wouldn't have to deal with oil in the weld.  If you drain the oil first.  Make it star shaped or something, so it looks like intentional art, not a patch.

I still wouldn't do it.   Slim chance of success.  Higher chance you'll have oil burning inside.

You could flush the engine after you drain the oil.  In that case leave the hood open as you weld, so that when the valve cover blows off it won't dent the hood.

OK. believe it or not.  One time had a pinhole leak.  Drilled the pinhole and inserted a steel shaft pop-rivet.  Has not leaked for 7 years.  Just saying.   

The roofing industry has closed ended pop rivets with built on rubber sealing washers. That would be my try.

I fixed a leaking aluminum pan on a POS pontiac g6 once with some of the stick epoxy stuff.  Put the vehicle up on stands, drained the oil, cleaned the crack very, very well with a whole can of brake clean, let it dry, forced the epoxy stick/putty into the crack, smeared the rest of the stick all around the crack.  Let harden overnight, refill.  It's still holding a year later, as far as I know. 

Depends on the location.  If said hole is in low part of the sump away from the pick up drain oil, hose inside and out with carb cleaner (NOT BRAKE CLEANER!) Blast air in drain hole to remove vapors and put and oil out the crack.  Do a final wipe on the outside of crack. Then pass a flam by the drain plug hole no POP your good to go if it goes pop reclean an give it more time to evaporaite.  I've brazed a oil pan on the side of the road in my school bus some 30 years ago.....holy crap how did i get old?

Streetwiseguy said:

Take the valve covers off and weld away.  That way, when the fumes in the pan explode, the forces will go up, and you won't be killed, just badly burned.

I had to modify a 9-quart pan for header clearance on a big block Ford.  This was done off the car, and someone else TIG welded it together.

Well, after getting it all back together we found that one of the welds was porous, and it was absurdly labor intensive to get the oil pan off (engine had to be out, and header R&R with 3 piece headers SUCKS, and a dozen other reasons) so my plan was to drain the pan, thoroughly drench the pan outside and in with carb cleaner, using a long straw to get to the weld area through the drain plug, then flush the inside of the pan with argon and weld it up.

In my haste, I missed step three. After about ten seconds of welding, it ignited the carb cleaner vapors in the pan.  Boom. It turned the pan kind of into a dumpling, and opened up the crack to where I could see it easily (so it wasn't all bad).  The push-in valve cover breathers landed on the other side of the building, and it pushed the rubber valve cover gaskets completely out.  So, I got to redo the valve covers, which involved removing the master cylinder and brake booster, because Ford.

But once it poofed, there was no longer an ignitable mixture inside the engine, so I could weld in peace.

BTW, if you go the epoxy route, use a fuel tank repair kit.  It is like JB Weld but has an extremely aggressive cure period.  It is mixable for about five minutes, you slather it on, maybe with the supplied little patch of fiberglass they give you, and you sit there keeping it from dripping off and wondering if you mixed it wrong.  Then like a switch it gets VERY hot and sets up in about ten seconds.  An hour or so later and it's permanent.