I have a Grimmspeed catted j-pipe on my 2017 WRX where the cat is starting to rust. Oddly enough, just the cat is rusting and the rest of the pipe looks pretty good. The pipe was installed by JMA back in January this year. I will be modifying and reinstalling the shifter plate cover for the Boomba short shift plate I recently installed, so the car will be up on a lift. I figured since it will be up and easy to get to, I may as well address the rusty cat. I am planning to use Por15 high-temp paint to paint over the cat to stop the rust and prevent further corrosion. For prep, I am going to lightly sand and scrub off any loose rust and surface dirt, as well as degrease the bare metal. Since this is an area exposed to the elements, I'm thinking several coats would be beneficial. Has anyone used Por15 high-temp paint on their exhaust pipes? If so, how well did it hold up? Would a different paint be better to use? Should I just paint the cat or should I go ahead and hit as much of the exhaust as I can to prevent inevitable rust? I have the j-pipe mated to a resonated Cobb catback. Thanks.
If it's not stainless, I would paint it. I love POR15, I used the high-temp on the headers on my 4Runner (gets driven very little, and never in the winter...), and I just put a couple coats on the mid-pipe that I replaced on our Outback. It's held up well to daily driver use since April... The headers were pretty rusty, so I had them sandblasted, and the mid-pipe was a brand new Walker piece that I cleaned up with a wire wheel. In both cases I washed with POR15 Marine Clean, treated with Metal Ready, and applied several coats. But POR15 can be painted right over rust, as long as it's not flaking off. I took this picture when I finished the Outback. Not the greatest angle, as I was mostly showing the repair flange for the rusty axle back. 20180427_212858 by Numbchux, on Flickr And of the headers, immediately after install. But they still look like this. 2018-06-19_11-37-47 by Numbchux, on Flickr
Looks nice! The j-pipe is listed as stainless on the Grimmspeed website. I would assume the cat also is stainless, but perhaps there is something to do with the catalyst materials inside and causing rust?? I am under the impression that even stainless steel will rust, just not as much as non-stainless. Suppose I'll look at painting the cat if not the whole exhaust.
My neighbor who makes mild steel BBQ smokers swears by using high heat primer, then high heat paint which I am going to try on my mild steel project. Though now @Chux has me thinking about POR15 after showing of his headers....
Have you contacted grimmspeed about it? I'd at least ask them since it sounds like a pretty new part.
They have excellent response time! Sounds like the entire pipe is stainless 304 steel, but the cat gets a brushed finish that tends to show some surface rust. At any rate, they offer a lifetime warranty so if it ever rusts through, I'm covered.
