Water is a product of combustion of either gasoline or diesel fuel. The key to not having your exhaust system rust away is not driving short distances where the vapor condenses and sits in the cold muffler after shutdown. If you drive long enough to warm the engine (15+ minutes) you will get most of the water that collects when it first starts up to evaporate and greatly reduce the tendency for the exhaust system to rust.

The middle pipe on my E300 broke off of the muffler from rust and I found a shop who fabbed a new one and welded it back good as new since everything else in the system was pretty sound.

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Marty D.

2013 C300 4Matic
1984 BMW 733i
2013 Lincoln MKz