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I think all cars exhaust pipes get very rusty after not very long. Why is that?

I know that the pipe gets extremely hot, but how come that makes it rust more than any other part of the car?

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A lot depends on your location - if the roads are salted where you are, that will contribute massively to the speed with which the exhaust will rust. I have a couple of cars that are still on the original exhausts after 18-20 years, but they both ran in a salt-free environment. –  Timo Geusch Jan 2 '13 at 0:03
    
My MR2 still has its original exhaust system (22 years old now) and is run year round (I've had holes in the floor replaced 3 times). My (18 year old) Eclipse which is rarely run in the Winter is now on it's third exhaust system (1 stock, then an aftermarket stainless steel, now a custom built stainless steel) due to rusting them out. –  Brian Knoblauch Jan 2 '13 at 12:43
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1 Answer

Various reasons:

  • It is close to the ground - where you have water, salt, grit etc.
  • It is typically not made of rustproof metals, but is considered a consumable, with portions like the catalytic converter being relatively short lived, so spending lots extra to protect it would be pointless.
  • The exhaust gasses include corrosive gases such as sulphur dioxide, which becomes an acid when mixed with the water in the exhaust

That said, most of my exhaust (the portion after the catalytic converter) is stainless steel, so it doesn't rust and looks pretty nice when I polish it. It cost a bit though.

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