Let's say I was to buy a stainless steel magnaflow muffler. From what I read, the inside packing is stainless steel mesh. Stainless steel should not rust.

The easy answer is the muffler will sound louder as it gets old.

For those who actually have magnaflow or similar stainless steel mufflers on their cars for 10-15-20 years, can you offer an actual review?

Does it actually last a "lifetime" of the car?

 

You should count miles in there also. I have 120k on my Escalade with stock stainless muffler. It's louder than when it was new, but still works. Magnaflow makes great stuff and if I ever want a performance exhaust, it's my first choice.

 

I have a ss bmw muffler down at the shop that must be from the 80's. Somebody placed a old billboard post on it (about 20 feet long of 4 foot wide steel tube) so I haven't been able to throw it away. It still looks pretty good.

Just make sure it's welded on properly (ss filler and the right gas) or the welds will rust just like any other mild steel part. I had a shop put magnaflow mufflers on my truck about 13 years ago, but they used normal steel for the tubing and welding then painted everything with a anti corrosive coating. You can see rust forming on everything but my jethot coated headers and SS mufflers.

I have some magnaflow ss cats on my e38 though, and I don't think they get hot enough in the winter. It will give me engine lights for the cats whenever it's below 50 degrees or so. Luckily my car gets tested in the summer.