Looked at the pic in the other thread. That ain't right. On my '05 the headers might have been blued at one time (they are a nice gray patina now) but the intermediate pipes back after the cats have never discolored at all. And I'm close to 50k miles on mine.
For that amount of exhaust heat to be generated that far back I'd expect there to be some kind of a fueling problem that is dumping raw fuel in the exhaust to be combusted in the cats. What has your fuel mileage been? Do you have a PCIII installed? Is the O2 sensor still connected and functioning?
Note that, unlike many fuel injected engines, the O2 sensors can be disconnected completely and the ECU will not throw any check engine codes. When the ECU senses the missing O2 data it just falls back into an "open loop" mode, just like it does on warm up before the sensor comes up to temp. MAny folks (like me) intentionally disconnect the O2 sensor and use a PCIII. THe PCIII map actually considerably leans out the mixture from the base open loop map in a good portion of the section of higher rpm, higher throttle position operation.
If your O2 sensor was (intentionally or unintentionally) disconnected and you do not have a PCIII to lean out those cells of the map, I could see that causing a too rich mixture that would have the cats working overtime. Could the PO have had a PCIII and removed it before sale, but forgot to rehook up the O2 sensor?
