Why does a rust hole start at top center of muffler? Snow/salt crud sitting on top? Just happen to be where a weld point was? I know sst does not last forever but wonder why holes appear in various places.
interesting that 80% of taurus’s have rust in this spot at junkyard.[quote=“Cavell, post:1, topic:95721, full:true”]
Why does a rust hole start at top center of muffler? Snow/salt crud sitting on top? Just happen to be where a weld point was? I know sst does not last forever but wonder why holes appear in various places.
I assume they just have to start somewhere. I wager to say that most holes start on the side and not on top or bottom because that is where the metal is a touch thinner due to the bend. Just guessing.
My guess is that it has a great deal to do with the exhaust’s path in the canister… including turbulence. My guess is that the internal pathways cause heat and sulpheric exhaust components to concentrate in the spot that ends up being the first breech. That’s only a guess, however.
Stampings cause variations in the thicknesses of the metals too, and that may be the reason. Or perhaps a contributor. Again, just a wild guess on my part.
To really find out would be simple: run a temp map of the canister when fully hot and/or perform a dynamic analysis of its flow and turbulences on a computer model. Of course the program for this probably runs $20,000 or more and the engineering to input the data would probably cost another $10,000. I might even be being very conservative. I’m guessing, of course. And then you’d have to do a separate analysis for every muffler design.
I’d say that’s an aluminized muffler (aluminum coated on carbon steel) which is much more prone than stainless to attack from salty sludge sitting on it.
Engine exhaust is primarily carbon dioxide and water.
The carbon dioxide and other combustion products make the water acidic, perfect storm for metal corrosion.
Yeah, looking at the location (right at an internal baffle), it does look like inside-out rusting. Why the top?..well, it’'s probably hotter there (less air flow) and reactions are accelerated by heat.
It looks to me like there is a structural component inside, right below the bigger hole. At some point, that outer metal wrap comes in contact with inner structure. Sometimes, they are even spot welded at points like that. The aluminized coating gets rubbed off by thermal expansion and contraction over time, the acids and water vapor do their magic and ta-da, a hole develops.
Agree with other here, looks like aluminized steel. The exhaust stream is largely water vapor, as @circuitsmith posts. That stuff, and nasty byproducts like oxides of sulfur, condenses in the cooler muffler, especially on short trips and attacks any point it can so rust begins in a place protected from the elements.
Welding leaches out the rust-protecting properties of both aluminized and stainless steels. Leaches out the nickle and chromium which keeps stainless steel from rusting. Just look at the seams on your stainless steel exhaust system, they show rust first. And the 409 stainless used in modern exhaust systems certainly LOOKS like it’s rusty when it gets old. Even aftermarket 300 series stainless parts corrode at the welds first.
