Our 2010 NF Sonata (well over 200K miles now) failed safety inspection when the inspector finally found the busted pinch seam in the muffler that I had been willfully ignoring for several years. The shop helpfully quoted around $1100 to replace the exhaust system, including the second catalytic converter. They justified this by pointing out the system had really rusty flanges and they weren't going to be able to get things apart neatly. It would also take over a week to get the parts together.
Reviewing the quote, and to my surprise, they were only asking for a small amount of money for labor. Additionally, the parts were aftermarket!
I am morally opposed to replacing catalytic converters that are not completely destroyed. They are expensive parts and there is a small chance car goes to a state with weird emissions rules that doesn't accept working parts that aren't certified. So I declined the service and took the car home, pink badge of shame proudly in the window, and resolved to fix it myself and use my welding skills to make up any gaps originating from rusty flanges and reuse as much of the old system as possible.
Without doing due research I ordered a muffler and resonator kit (Walker SS) from rockauto for far less than the shop quote. When these parts arrived, it was clear that they have a lot more galvanized steel than the OE parts. It seems like just the body of the muffler is stainless while the resonator and pipe is galvanized steel. I instantly regretted my purchase and actually spent time to see what other options existed between the basic kit and the expensive Hyundai original muffler.
Further study showed that API makes a muffler (API 29927-07553709) that looks identical to the OE muffler (Hyundai 287003K520), but for a fraction of the price. Also, given the shipping time, had I realized that the Walker kit had so much galvanized I would have made a junkyard run to see if I could get used unit. Most cars made since 1999 or so have much better exhaust systems than old cars, so I would bet that a junker that hadn't spent much of it's life swimming in salt would have a nearly pristine muffler.
When I started the replacement, my goal was to use as much of the old system as possible. The Walker unit has a flared joint where the unit attaches to the centerline exhaust mid pipe, so I cut the old unit there. Unfortunately the flare was just narrow enough that it wouldn't fit on the OE system.
It was disappointing to find the Walker SS muffler was considerably lighter than the OE unit once I had it cut free of the car. Less metal, less stainless, so I surmise, shorter life.
I hopefully tried to disconnect the rusty flange at the resonator so I could just bolt in the new midpipe at the flange. While they were quite rusty, once I started attacking them it was also apparent that there was quite a bit of metal left and they were at no risk of failure. After a couple of hours of struggle, I gave up and cut the midpipe and resonator flanges too (it seem like the bolts in the flanges were pressed in as studs) and resolved use 2 1/8" couplers I had on hand or weld it together. The couplers worked! But sadly, now the car has lots of galvanized steel in its exhaust.
Astute readers may recall that I was replacing mufflers an pipes in a 1990 Oldsmobile every 5 years or so.
IF I were to replace this system again (big IF, I doubt it has 4 years of road life left given mileage and rust elsewhere). I would approach this very differently.
Take aways:
First: Look for a junkyard muffler, API or other muffler that has the ribbed stamped body. .
Second: having a collection of 2 1/8", 2 1/4", ID/OD couplers on hand would make it easier to replace just the muffler and not a lot of pipe. Especially if these were stainless.
Third: An exhaust pipe expander would have let me expand the flare on the new muffler, and saved hours of work. The NF 2.4L sonata seems like it's 2 1/8" OD pipe, but there's a lot of complex bends...
