HELP! Best way to seal cat flange

cat flange is warped aswell so even with new gasket and bolts it still leaks.
any suggestions because my gas mileage is FKD and my truck is crazy loud because it’s leaking on both cats
Anyone know what gasket this one is on upstream cat i’m thinking double up flanges might work??

 

I assume that picture is before you replaced the gasket and hardware?

 

I have something called exhaust sealant or something like that. It’s buried deep in my tool box. I’ll get you a picture tomorrow.

 

okay thanks bro

 

i think this is after, look at that huge gap it’s warped to shit

 

Yeah, and are those fasteners going to just snap off. Start spraying some good penetrant on them.

 

Sorry your first post is confusing, says even after a new gasket and bolts it still leaks. The picture looks like old rusty bolts.

 

First read the title as "steal"

 

typically exhaust flanges get cleaned and can be lubricated with certain grease
and new gasket

which doesn't look possible here given the rust. Might be time to consider:
-having an exhaust shop do some welding
-replace with better condition used
-new cats, non-CARB is cheaper than CARB

yes there's other stuff like exhaust sealant out there, clamps, etc.

 

Go to an exhaust shop. None of the over the counter fixes will seal a flange that badly warped

 

This.

@mark06yoda It'll be cheaper in the long run if you do it right the first time. If you don't want to replace both the headers and the y-pipe, have an exhaust shop chop and weld a new flange. Its a relatively cheap job compared to new exhaust components.

-J

 

bro so will they cut the flange on the pipe
side not the car side right because how are they gonna weld it back on the cat?

 

I would have them either cut both flanges off and weld 2 new flanges on there, or cut the flanges off and weld a pipe in place. If you don't have any plans on replacing the cat or catback, then option 2 would be cheaper. In either case, both flanges will need to be cut out. From looking at the 1 picture posted, the middle of the flanges are thinner than the edges where the bolts are. Likely, the exhaust has blown out that area because the flanges were so rusted that the exhaust just started to erode it. If that's really the case, I would have the rest of the exhaust pipes inspected. It might be time for a new catback + cat. I don't know where you live, but if you get road salt, I'd suggest replacing the cat and catback since your truck is almost 20 years old.

 

man i don’t think my cat is bad just the flanges or possibly o2 it is hard to tell but i do have a po420 and po430 code

 

You should have it inspected. Cats do fail over time as well. Nothing lasts forever in any vehicle. Considering the rust issue you're having, putting a bandaid on it will just make it worse later on.

 

having an exhaust leak like that can definitely throw cat codes (even if the cat itself is fine) when they're close to the O2 sensors especially the leak is upstream of the O2 sensor. I used to battle this with my subaru all the time, cat was still working great but flanges were toast. After going through gaskets and sealant for a while it eventually got bad enough and I got fed up enough that I just welded the flanges together solid lol, no more leaking. Was worth it for me over replacing the headers and cats on something that wasn't worth the money

 

ohhhh i see but how can you weld rusted metal, just clean it up as good as you can?
and how do you inspect cats? i hit it hard but didn’t hear any shaking so i think it’s good

 

Go to an exhaust shop and have them weld on new cats. That upper flange looks very thin due to rust.

 

I like this idea best. Weld them together. It’s not a bandaide, it’s a cast.

 

I just cleaned it up with a wire wheel since the metal that was left was rusty but not rotted. It wasn't pretty but it didn't take too long with my cheap electric mig and was fine after that. Of course the "right" fix is to replace everything but wasn't worth the money for me.

I knew the cat was fine because it would only start throwing the code once I let the leak get bigger, every time I sealed it it would go away again for a while. Depending on exhaust shape if you unbolt the flange you can look in with a phone camera and flash and see the catalyst in there and its condition. Rattling or glowing red and getting really hot would be an indication of it being shot or clogged.