[Countrywelder]

My Honda mechanic told me I have a crack on my exhaust muffler that houses the catalytic converter. A 2004 Honda civic. He said it goes mostly all the way around and is stainless steel. Not having welded a muffler before, I 'm sure someone out there has done something similar. How thick would the stainless steel be? If I can get the muffler off and to my shop and tig weld it, would it be so thin that it would be very difficult to weld. I 'm reminded that working with rusted steel, many times the entire area is so thin that the steel just disappears/evaporates when you start to weld it.

[Diesel]

Best advice is to replace IMO. I believe exhaust is usually around .035-.040? That's what I've seen anyways. And with it being rusty and dirty it is definitely not going to weld very well at all. Very intense cleaning required and still might have enough impurities to crack again. Best to spend 40-50$ and just get a new one

[exnailpounder]

I fixed a muffler for my stepson by re-skinning it. I had some thin stainless, 18ga. I think, and I wrapped it around the muffler and tig/spot welded the seam. Got him through emissions testing and lasted about 2 years before the muffler just fell apart....but the skin was still good. Trying to weld on an old contaminated and filthy dirty muffler would be near impossible.

[Artie F. Emm]

that houses the catalytic converter.

The OP said "muffler" when he may have meant "catalytic converter " which may change the conversation. A muffler is a bolt-on at the back of the car and because they're <$100 it may be better to replace than repair.

The CC is expensive enough that it may be worth repairing: check out the cost of a knock-off and the OEM.

The CC is amidship and not easy to get at. I replaced my exhaust system (95 Integra) by jacking up the car and lowering each tire onto concrete blocks. Most if not all the nut/bolt connections had fused with rust and i had to cut them off: if your mechanic will remove it for you then i'd let him.

Back to welding on dirty stainless: doesn't the need to back-purge and prevent sugaring apply?

[sedanman]

I have repaired a few cat converters by cutting the pipes off and then welding a "fit kit" onto the main body of the converter. I don't know of this is an option for this application as even aftermarket converters fit like oem so there may not be a fit kit available. Basically the cats were "universal " in nature and there was a fit kit to mate it to the vehicle.

[big gear head]

It will be a catalytic converter or a muffler, not both. I'm guessing this is the converter. They get hotter than the rest of the exhaust system.

Most OEM exhaust systems on late model cars and trucks is 409 stainless steel. It won't be rusty. It will have carbon and other exhaust contamination in the crack and it will be hard to get it out, but welding over it shouldn't be too hard. I would use 410 or maybe 309 wire on it. It's probably worth trying.

[DSM8]

Another option might be to tack weld along the crack then treat it like AL and put a band around where the crack is, twice the amount to weld but you wont have the contamination issue of trying to weld the entire crack itself...
Just an idea