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I've seen a lot of videos where it appears the mufflers on new corvettes appear to be rusting where the exhaust tips meet the muffler - is that an issue with these cars?
I'd be willing to bet the exhaust system components on Corvettes (and most other modern cars) is stainless steel except for the exhaust manifolds, which are cast iron.
The surface rust on the weld areas is the result of overheating the stainless steel, which causes some of the rust-inhibiting alloys to migrate away from the weld area. Good welding technique will leave a straw color in the welded area which will not rust.
I don’t know if classifying it as an issue is correct, but there is rust on the welds. The mufflers are aluminized steel so they shouldn’t rust but the welds themselves are suspectible to it. My 2017 has a bit of orange on the welds when it was new. I’ve seen this on a lot of C7’s.
You should look at the rust accumulating on the exhaust manifolds..
I'd be willing to bet the exhaust system components on Corvettes (and most other modern cars) is stainless steel except for the exhaust manifolds, which are cast iron.
The surface rust on the weld areas is the result of overheating the stainless steel, which causes some of the rust-inhibiting alloys to migrate away from the weld area. Good welding technique will leave a straw color in the welded area which will not rust.
I've seen a lot of videos where it appears the mufflers on new corvettes appear to be rusting where the exhaust tips meet the muffler - is that an issue with these cars?
Only cosmetic! The welds themselves turn brown quickly. Next to the welds the very, very thin aluminum coating is gone. I have used a very simple, under $10 solution that held for 3 1/2 years on my C7 Z51 and have used in on my Grand Sport. The exhaust system vendor (who I think is still Tenneco) no doubt used the same stainless welding wire as the mufflers. It is 409 stainless and has essentially no Nickle and only ~10% vesus 18% Chrome, 8% Nickel in "shinny" stainless. Works fine for mufflers but turns brown quickly but is far less expensive than the 304 stainless on my Street Rod Bolra Mufflers. The aluminized coating makes it look better longer!
Here is a PDF with more info than you may want about exhaust materials and a detailed How To of what the picture below shows, the use of "Rust Reformer." Paint will peel and if you look at were it is, not easy to do even with a paint brush unless you take parts off! Rust Reformer can be done in 15 minutes and no need to remove anything! http://netwelding.com/Muffler_Rust.pdf
Bottom Before: Top After. Rust Reformer is NOT a paint it turns iron oxide a blue black and does nothing to none rusted parts. Goes on like water.
Note perfect, but when you look from the rear you don't see brown!
I'd be willing to bet the exhaust system components on Corvettes (and most other modern cars) is stainless steel except for the exhaust manifolds, which are cast iron.
The surface rust on the weld areas is the result of overheating the stainless steel, which causes some of the rust-inhibiting alloys to migrate away from the weld area. Good welding technique will leave a straw color in the welded area which will not rust.
That is a pic of 304 or what is called 18 (Cr)-8 (Ni) stainless it stays shinny! Most car mufflers are made from cheaper 409 stainless that only has ~10% Chrome and essentially no Nickle. It oxidizes BUT looks better much longer than carbon steel.
I would also say the shielding on those welds was not as good as it could be. This is a pic from a shop that does high quality work. The heat affected zone (HAZ) next to the weld will oxidize at the high temperatures it reaches. However the welds don't have the oxidized straw color.
Pic of aluminized 409 stainless right versus non aluminized left after corrosion test. One of many pics in my PDF above.
Only cosmetic! The welds themselves turn brown quickly. Next to the welds the very, very thin aluminum coating is gone. I have used a very simple, under $10 solution that held for 3 1/2 years on my C7 Z51 and have used in on my Grand Sport. The exhaust system vendor (who I think is still Tenneco) no doubt used the same stainless welding wire as the mufflers. It is 409 stainless and has essentially no Nickle and only ~10% vesus 18% Chrome, 8% Nickel in "shinny" stainless. Works fine for mufflers but turns brown quickly but is far less expensive than the 304 stainless on my Street Rod Bolra Mufflers. The aluminized coating makes it look better longer!
Here is a PDF with more info than you may want about exhaust materials and a detailed How To of what the picture below shows, the use of "Rust Reformer." Paint will peel and if you look at were it is, not easy to do even with a paint brush unless you take parts off! Rust Reformer can be done in 15 minutes and no need to remove anything! http://netwelding.com/Muffler_Rust.pdf
Bottom Before: Top After. Rust Reformer is NOT a paint it turns iron oxide a blue black and does nothing to none rusted parts. Goes on like water.
Note perfect, but when you look from the rear you don't see brown!
Hey JerryU, I read your PDF on this subject. Thanks. I'm going to examine my GS for any rust in the areas you mentioned in your PDF. I'm curious, did the Rust Reformer do for your headers what it did for the exhaust welds?
Hey JerryU, I read your PDF on this subject. Thanks. I'm going to examine my GS for any rust in the areas you mentioned in your PDF. I'm curious, did the Rust Reformer do for your headers what it did for the exhaust welds?
As I show in the PDF, tried on the cast iron exhaust manifold and it helped some but not as much. Perhaps they needed to have more "rust!" Cast iron is a totally different chemistry and does not rust as quickly as the 409 stainless welds and the areas where the thin aluminized coating is gone..
As I show in the PDF, tried on the cast iron exhaust manifold and it helped some but not as much. Perhaps they needed to have more "rust!" Cast iron is a totally different chemistry and does not rust as quickly as the 409 stainless welds and the areas where the thin aluminized coating is gone..
JerryU, thanks once again for leading the way and showing others the path you took. Your PDF's are very appreciated. My Grand Sport is a little more than 8 months old and after reviewing your posts, and then your PDF tutorial, I thought I'd better look at my own exhaust to see if mine too had some oxidization on it. Sure enough. Check out these before and after photos.
Before
Then I coated the shizit out of any/all oxidization I could find!!!
Despite my "liberal" application, it appears as if I missed a few spots. It's not easy working in that tight little window with an extended brush, while laying on the floor. I think I'll apply a second coat as you recommend and coat the spots I missed the next time I have it up on the ramps to make it easier to see and work on. I'll probably remove any excess rust reformer at that time too.
Any more advice? How about telling me what you did to remove any excess reformer (not that you had as much excess (or any) as I have)???
As I show in the PDF, tried on the cast iron exhaust manifold and it helped some but not as much. Perhaps they needed to have more "rust!" Cast iron is a totally different chemistry and does not rust as quickly as the 409 stainless welds and the areas where the thin aluminized coating is gone..
Your education on this topic and the mitigation one can take was not only educational but very useful.
Thanks to you I used the Rust Reformer and the results were excellent.
JerryU, thanks once again for leading the way and showing others the path you took. Your PDF's are very appreciated. My Grand Sport is a little more than 8 months old and after reviewing your posts, and then your PDF tutorial, I thought I'd better look at my own exhaust to see if mine too had some oxidization on it. Sure enough. Check out these before and after photos.
Then I coated the shizit out of any/all oxidization I could find!!!
Despite my "liberal" application, it appears as if I missed a few spots. It's not easy working in that tight little window with an extended brush, while laying on the floor. I think I'll apply a second coat as you recommend and coat the spots I missed the next time I have it up on the ramps to make it easier to see and work on. I'll probably remove any excess rust reformer at that time too.
Any more advice? How about telling me what you did to remove any excess reformer (not that you had as much excess (or any) as I have)???
Originally Posted by Maxie2U
Your education on this topic and the mitigation one can take was not only educational but very useful.
Thanks to you I used the Rust Reformer and the results were excellent.
Thanks guys. The effort to document what I do is worth it when I get those comments! It's fun and being semi-retied since 1999 I have the time!
Since I have used this method twice on my Z51 and Grand Sport I can see from the pics you put on much heavier than I did. I used two light coats ~20 minutes apart. My guess is you could wash with some soap and water and where there was not rust it should come off.
I have the very same issue on my '18 Vette I recently purchased....not so much the weld joint themselves but on the rear muffler housing surface (see pic below)
Most of the other new Vettes on the Dealer's lot also showed similar discoloration and rust on the muffler housing end plates...
Think I'll try some rust restorer and then install an exhaust port filler plate...
Be sure to get the clear milk looking liquid! This week removed my rear diffuser to install a C7 Carbon lower section with 4 fences, improved diffuser. Thought since I'll have it off would touch up any new rust spots and those that were hard to access. The product said shelf life is a year so wanted to get a new container. Walmart did not have the container of milk colored and consistency material. They only had a spray can that said the same thing, Rust Reformer. It said "ready to paint." So thought I was buying the same product is spray form and since I would have good access why not!
It is NOT the same product! It also contains a black paint! Without the access I had by removing the diffuser (don't think about it just to paint the muffler as it is not easy) it was OK and I didn't have that much extra rust. Checked and the original material is available on the Net-check Amazon. Easy to apply but as reported above and I did not emphasis in my PDF no need to apply excessively. Use several light coats with a long handled brush waiting 30 minutes between. Made my brush with a cheap small parts brush taped to a thin piece of wood. Just get it on so the checical reacts with the rust, as no brush strokes etc will show,
Recently purchased from Walmart left; Milk looking and consistence right purchased 1 year ago. New stuff has black primer and is NOT the same!
This is the How To..PDF: http://netwelding.com/Muffler_Rust.pdf
First thing I did when I got my car was buy a can of black BBQ paint and spray the rear facing surface of the mufflers.
Hey C5Driver, how does that surface look now? Did the paint stay on? Does it look good? I'm presuming that you really can't see the surface any more because it's black, and if you can't really see it any more (compared to before painting the surface) it looks better than being able to see a stained/rust colored blotches on the surface of the mufflers???
02-16-2018, 12:05 AM
Muffler rust?
That is a pic of 304 or what is called 18 (Cr)-8 (Ni) stainless it stays shinny! Most car mufflers are made from cheaper 409 stainless that only has ~10% Chrome and essentially no Nickle. It oxidizes BUT looks better much longer than carbon steel. 
It's not easy working in that tight little window with an extended brush, while laying on the floor. I think I'll apply a second coat as you recommend and coat the spots I missed the next time I have it up on the ramps to make it easier to see and work on. I'll probably remove any excess rust reformer at that time too.
