When I heard that the MCS exhaust was stainless steal, I figured my days of exhaust replacement were over. Now I've read that some stainless steal is susceptible to rust from road salt (not sure if that is true or not).

The two things that have done in non-stainless steel exhaust systems on my past cars were 1. winter road salt and 2. driving very short distance that didn't allow the exhaust moisture to evaporate. Will either of these be an issue with my MCS exhaust?

The answer to this may help guide me in exhaust mods. For example, wait till the stock one rusts off before replacing it with an after market exhaust one, or doing a one ball if rust isn't an issue or choosing the correct materials for an after market exhaust.

 

I don't think the stock exhaust is stainless steel. Most stainless steel exhausts use 300-series stainless steel (austenitic), which is non-magnetic or nearly so.

I just checked the stock exhaust on my wife's car with a magnet, and the magnet stuck *hard* to the resonator housing, the muffler housing, and the exhaust tubing.

 

As far as I am aware the exhaust is mild steel not stainless. I'll wait until mine rots off and then replace with an aftermarket SS one.

 

You'll be waiting a long time for it to rust off. I just replaced mine on an Feb 03 MCS after 84k and it'still looked fine after I took it off. The SS tips even looked good. I was going to wait for it to fall off as well but just got tired of waiting.

 

SS does not rust (i.e., oxidize) from road salt, but most grades do tend to crack in the presence of the chloride ions from salt. Three factors are involved: chloride concentration in water (more than 50ppm), heat (greater than ~70 C), and stress. Driving on wet salty roads, the first two conditions are easily met. The reason most SS exhausts don't crack is that the stress levels are probably low, below some critical threshold for crack propagation. But I think it is a good idea to minimize salt exposure to a SS header or exhaust. Keep in mind that this environmental stress cracking potential is reversible, i.e., if you wash the salt off, the problem disappears.

 

It is indeed stainless, but there are many grades of stainless. 300-series is nonmagnetic and resists chloride pitting for marine (saltwater) and tableware use due to its high chromium and nickel content. Cheaper magnetic 400-series (no nickel) is commonly used for automobile exhausts and lasts about 4x as long as mild steel in that application (some combustion products are acidic and will eventually eat it away from the inside out).

Note too that stainless still rusts unless the surface is passivated with strong acids. This removes the iron from the surface and leaves only chromium (and nickel, if any) exposed to protect the underlying iron from corrosion. From the looks of both my MCS and JCW pipes with their surface rust this step was omitted. The JCW cans and tips still gleam though, so those were properly passivated.

 

BFG9000, are you absolutely certain it is stainless? I only ask because after 2 Central New York winters, my stock MCS exhaust was rusted HORRIBLY. When I replaced it with my new Milltek cat-back, the nuts were totally seized up with rust, so much so, that after soaking them for 24 hours, they still wouldn't break free. I had to grind them off. The pipes were covered in a highly-textured rust coating. I find it really hard to believe these pipes are stainless steel...

 

I had my stock 05 MCS exhaust replaced at AMVIV this past weekend and there were partially failed weld joints on both points where the tubing enters the rear cans, and both had obvious signs of rust in the joints. This is an MCS that has spent most of its life garaged and in Arizona, where rust is pretty hard to come by, but with the failed joints, im sure it caused a place for moisture to sit and eventually begin to rust through.

 

I've actually welded on the stock MCS pipes and they appear to be the same cheap stainless that most OEMs use nowadays. Type 409 stainless is only about 50% more expensive than aluminized mild steel and frequently looks pretty rusty by even 3-4 months; it just doesn't rust through as quickly as mild steel. The surface will pit immediately if salt solution is splashed on it.

Fine quality aftermarket polished exhausts are often type 304, 309 or 316 which not only are far more expensive but are notoriously hard to bend without cracking, so OEMs hardly ever use such high-grade stainless steels for exhaust pipe. If you have such stainless it is important not to use carbon steel welding wire on it or it will actually rust out faster at the welds than plain mild steel from the galvanic corrosion.

I think if you asked your parents how frequently they had to replace exhausts in the olden days before stainless was widely used (this came about because it is now considered part of the emissions system so automakers are required to warrant it for 5years/50,000 miles), you would be surprised to find their "lifetime" warranted Midas mufflers regularly rusted out in as little as two years (of course providing an opportunity to sell other services).

 

I just made it through one winter, so I can probably just wait till it rusts off after next winter. Any recommendations for an after market exhaust that will hold up to short runs and winter salt?
Gee, usually people ask for a good sounding exhaust that adds more power, I'm asking for one that wont rust. Duh....

 

In such a salt-laden environment I'd look at brands that specifically advertise they use 300-series stainless like Borla. My car was from Hawaii so the salt air has even corroded all the unpainted aluminum on it.

BTW the stock hanger brackets look like mild steel so either those or the carbon steel welds will probably rust off first.

 

One thing you have to keep in mind about stainless is this - it "stains less." After a few months it's not going to still look all shiney and pretty.

 

Exactly. I work heavily with 316 stainless parts that are for marine applications and every part that has spent any time in the field has areas of rust. And as mentioned previously, 316 is the most corrosion resistant stainless steel that is relatively easy to obtain.