New car exhaust pipe rust?



I have a 2010 Subaru Forester with dual exhaust. The Y tube that connects the main exhaust pipe to the mufflers is heavily rusted. The dealer tells me this is a stainless steel pipe and only the coating rusts. That doesn’t make sense. Does anyone know the truth here?


read this web site…explains reason why …

If you are from downeast maine…add salt to equation


He may be correct. Hold a magnet against the pipe. If it doesn’t stick, the pipe is stainless steel. I’ll bet my morning muffins it is. If so, you need not worry. The rust may be from some iron that’s been brought to the surface of the pipe in the drawing process.

I should add the disclaimer that I’m guessing here not based upon knowledge specifically of the process of forming stainless steel pipes, but more from general knowledge of having worked with stainless steel in other capacities.


Is there a metallurgist in the house? There are different types of stainless steel. They have different balances of corrosion resistance and strength. To put it quite simply, you can have exhaust system stainless that is relatively strong meaning resistant to cracking and bending under physical stress, high temps and temp cycling, but will have a layer of oxidized metal. OTOH, you can have flatware stainless that will be bright and shiny forever, but can?t take the physical stress. Don?t try to make an exhaust system with the latter.

It does trouble me a little that the y-pipe is the only pipe corroding if the whole exhaust system is stainless. If the y is stainless and the rest is galvanized, I am not surprised at all.


There are different grades of stainless steel and each has different properties against corrosion. And remember, it’s called STAINLESS steel not RUSTLESS steel.



I’m not a metallurgist but do ocean sail. Does that count ? There are indeed different grades of stainless depending upon the alloy content. Stainless is generally not a strong as most grades of steel but is more corrosion resistant over time which is more important. Nothing that we can afford is absolutely corrosion proof. I agree, I wouldn’t worry. A rust through of stainless will occur long after the rest of the body and motor have given up the ghost. Now, is that joint stainless ? I would be interested to look under other comparable models on the lot and check with the parts man.


The “stainless” used in automotive exhausts is a far cry from marine grade stainless fittings…It lasts a lot longer than the old thin-wall steel tubing, but it does NOT last forever. Lets just say it’s “rust resistant”…