Stock exhaust/cat question

[blue2000s]

Originally Posted by xclusivecar

Just had a cat replaced (under factory 7/70,000 mile warranty, thank god!!) and after seeing what the replacement would have cost me ($1100)!! I started to wonder...

1)Why do we have 4 cats?

2)When 1 goes bad can I expect another to follow in short order (kinda like the O2 Sensors going bad)?

3)The Porsche mechanic says they will only last 60-70,000 miles on most Imported autos due to the computer monitoring the exhaust flows very closely to pass U.S emissions. He says domestics do not have to monitor the exhaust flow as closely because of relaxed standards for U.S. made autos?!?!?! He says this is why most US cars Cats will literaly fall/rot off rather than set a code for reduced performance?!?!?!?!

Food for thought---$1000 per cat at the stealership @4 cats= $4000! Not something to look forward to...

A catalytic converter can theoretically last forever. There is nothing in the converter that is consumed in it's operation.

In reality, burned oil, sulfer and other impurities can coat the catalyst and hinder it's ability to do it's job, thus wearing it out. Excessive heat and vibration can also damage the materials that support the catalyst material.

This is why a malfunctioning O2 sensor or MAF can damage the cat. It can throw off the required mixture for the catalyst and will usually cause damage through overheating (too much O2 in the mixture) or coating with materials that keep it from doing it's job (too much HC and other rich combustion byproducts).

In general, though, a healthy car with an engine kept in good working condition should have a catalytic converter that lasts at least as long as the engine.

The mechanic is dead wrong. OBDII forces the use of upstream and downstream O2 sensors on all cars. There's no reason in general for an American car to have a longer lasting cat than a German one.

Cats work best at the normal operational (hot engine) temperature. There are 2 close to the exhaust manifold so that they'll be brought up to operational temperature quickly. There are 4 total cats to expose as much gas as possible to the catalyst material to maximize the amount of gas that's treated.

High quality cats can be had for about $200 each. There's no need to use the Porsche parts.