Surface rusting of Flanges

Bangkok_ZL1 · 10-13-2025, 01:30 AM

Anybody have suggestions to help with this? This is after only 1 year. I've just gotten back and decided to pull the Cats to inspect the innards. I noticed the flanges and gaskets had rusted some. I tried to get the face surface scoring off with some cleaner, but it really didn't work well. And ideas? I really don't want to reassemble this without a good solid seal. I had used this rustoleum on the cats outer shell before I put them on last year. As you can see, it didn't last long. I'm worried about the rust on the flange faces destroying gaskets.

SWFLZL1 · 10-13-2025, 08:28 AM

Hit them with a scotchbrite pad or some steel wool, they will seal okay after that.

bishopts · 10-13-2025, 10:01 AM

You might be looking a little too hard. It's normal characteristics of mild steel cats. The only way to prevent it is to never start the car. Or replace them with stainless steel.

KingLT1 · 10-13-2025, 04:18 PM

Talk about over analyzing. Don't go outside you might swallow a gnat.

Justcruising · 10-13-2025, 05:02 PM

Quote:

Originally Posted by KingLT1

Talk about over analyzing. Don't go outside you might swallow a gnat.

ZLRob · 10-13-2025, 11:02 PM

Quote:

Originally Posted by KingLT1

Talk about over analyzing. Don't go outside you might swallow a gnat.

I ignored this thread for that reason alone. Must have been posted on a Friday.

Bangkok_ZL1 · 10-14-2025, 02:52 AM

Quote:

Originally Posted by KingLT1

Talk about over analyzing. Don't go outside you might swallow a gnat.

Never tasted one.... how they taste,

Bangkok_ZL1 · 10-14-2025, 03:01 AM

Quote:

Originally Posted by SWFLZL1

Hit them with a scotchbrite pad or some steel wool, they will seal okay after that.

OK, the fact is they didn't seal well the last time. I saw the exhaust marks blowing between the gasket and the flange. I just already cleaned it off so you didn't see it. So, I will try what you suggest. I want a better seal if at all possible. My 1st inspection is coming up in just over a year and if Thailand deems my system which I did modify improper or unfit after all their testing, I'll be expected to import an entirely new stock exhaust system, probably 10K to ship it here and import duties. I know not everybody understands what it takes to have a "gray" market car legal in Thailand. So, I appreciate your suggestion.

Camfab · 10-26-2025, 03:58 PM

Quote:

Originally Posted by bishopts

You might be looking a little too hard. It's normal characteristics of mild steel cats. The only way to prevent it is to never start the car. Or replace them with stainless steel.

I have never heard of CAT's made of mild steel, perhaps some Chinese CAT knock off, even then I'd doubt it. Are you under the impression that stainless steel doesn't rust?

Stoner · 10-30-2025, 11:43 AM

Some people on this forum spend more time making smart ass remarks rather than attempting to answer your question or help you.

In my opinion what you are seeing is totally normal. Moisture collects in your exhaust as it cools down, so you will see some water or steam from your exhaust on cold startup. If you had an exhaust leak, as one person mentioned, scotch bright the flange, install a new gasket and torque to specification. I don't know the spec, just make it good and tight, then check for leaks. Every exhaust joint I have ever disassembled will look just like yours. It's totally normal.

Hope your inspection goes well.

KingLT1 · 10-30-2025, 04:29 PM

Quote:

Originally Posted by Stoner

Some people on this forum spend more time making smart ass remarks rather than attempting to answer your question or help you.

I have helped more people on forums then you can probably count to. It was just a joke and the OP knows that. He has messaged me before about other things.

10-13-2025, 01:30 AM	#1
Bangkok_ZL1 Flying around Thailand Drives: 2019 Camaro ZL1 Join Date: Oct 2020 Location: Bangkok, Thailand Posts: 620	Surface rusting of Flanges Anybody have suggestions to help with this? This is after only 1 year. I've just gotten back and decided to pull the Cats to inspect the innards. I noticed the flanges and gaskets had rusted some. I tried to get the face surface scoring off with some cleaner, but it really didn't work well. And ideas? I really don't want to reassemble this without a good solid seal. I had used this rustoleum on the cats outer shell before I put them on last year. As you can see, it didn't last long. I'm worried about the rust on the flange faces destroying gaskets. Attached Images __________________ Mods - From JRE, the 125 RWHP Kit; From FI Interchillers, the Stage I Interchiller system, 5mm Supercharger/Head spacer plates, Heater blanket; From BMR Suspensions, Motor mounts, Cradle lockout Bushings; From Misc, Train horn in the Abandoned Heat Exchanger location using the exchanger bracket. From Banks, An I-Dash to read it all...

10-13-2025, 08:28 AM	#2
SWFLZL1 Drives: 2022 ZL1 Join Date: Sep 2024 Location: SWFL Posts: 131	Hit them with a scotchbrite pad or some steel wool, they will seal okay after that. __________________ 2022 ZL1 M6 Coupe

10-13-2025, 04:18 PM	#4
KingLT1 Drives: 2016 1SS NFG A8 Join Date: Aug 2017 Location: 46804 Posts: 7,666	Talk about over analyzing. Don't go outside you might swallow a gnat. __________________ 2016 NFG SS A8/Whipple 2.9/Fuel System/Flex Fuel

10-13-2025, 10:01 AM	#3
bishopts Drives: 2017 2ss 6mt Join Date: Mar 2024 Location: dallas Posts: 1,612	You might be looking a little too hard. It's normal characteristics of mild steel cats. The only way to prevent it is to never start the car. Or replace them with stainless steel.

10-30-2025, 11:43 AM	#10
Stoner Drives: 2017 ZL1 HBM, M6 Join Date: Oct 2016 Location: Tucson AZ Posts: 272	Some people on this forum spend more time making smart ass remarks rather than attempting to answer your question or help you. In my opinion what you are seeing is totally normal. Moisture collects in your exhaust as it cools down, so you will see some water or steam from your exhaust on cold startup. If you had an exhaust leak, as one person mentioned, scotch bright the flange, install a new gasket and torque to specification. I don't know the spec, just make it good and tight, then check for leaks. Every exhaust joint I have ever disassembled will look just like yours. It's totally normal. Hope your inspection goes well.

User Name		Remember Me?
Password