Dynomax Ultra Flo Welded muffler rusting?

GTamas · Thursday at 7:47 AM

I noticed today that the Dynomax Ultra Flo Welded mufflers started having surface rust after two years. Only driven in spring/summer. The mufflers are supposed to be stainless steel according dynomax website.
Is this normal, or should I be worried?

07GtS197 · Thursday at 9:17 AM

Stainless steel can still rust when exposed to water. Certain grades will rust more than others. But it shouldn’t be deep. Have you tried scraping it? It’s probably a little bit on the surface.

badass98svt · Thursday at 9:30 AM

As mentioned, stainless will still have rust on the surface. Take a look at some of the Cyber trucks.
I have the same mufflers. They are my favorite sounding muffler that I've ever used.

cobrajeff96 · Thursday at 9:37 AM

The 400-series stainless will rust and still be slightly magnetic compared to 300-series, some of which are largely considered to be rust-proof. What you have is most likely 409 stainless because it's cost-effective (cheap). Occasional wire brushing and a small application of Surface Shield (or similar in your area) will prevent it from rusting all the way through. That's why these days you always have to check what exact grade of stainless the compound is. Only 316 or similar (within the 300-series) is considered truly rust free.

GTamas · Thursday at 9:53 AM

I learned something new today. :⁠-⁠) Thanks.

cobrajeff96 · Thursday at 10:22 AM

Sure thing!

96blak54 · Thursday at 10:44 AM

Well, a 409 series stainless grade has iron as part of its make up to aid in formability, but generally doesnt look rusty as what you have going on.

cobrajeff96 · Thursday at 2:15 PM

I think the Chinese market has something to do with that. Company's that use raw materials or even metalurgy (finished metals) from China unfortunately make claims that are sometimes untrue.

all steels have iron in them, it's just the amount of iron along with the alloy mix that determines the final properties.

I've had headers in 409 that got quite a bit of brown on them due to road salts and rainwater in general. 409 over time will not hold up unfortunately unless it's well cared for or just doesn't regularly see normal road conditions, nevermind harsh road conditions.

There's very few manufacturers of exhaust components making pipes in the 300 range and usually they are custom shops that do top tier hand-fab work. But I do have a set of Flowmaster DBX muffs I bought many years ago that have 316 outer shells that have sat outside for many years and they are still looking pretty new.