How hot can a catalytic converter get before it causes damage?

Dear Car Talk

Dear Car Talk | Jul 01, 1999

Dear Tom and Ray:

I have an exhaust question for you. How hot can a catalytic converter get before there is damage? The reason I'm asking is because a local muffler shop demonstrated (with some sort of heat-detection device) that while my engine was at normal operating temperature, my catalytic converter was approximately 900 degrees F. He said this is an indication that there is an obstruction of some kind in the converter. He recommended replacing it. Since the car is 13 years old, it seemed plausible, so I let him replace it. Was he right, or was I duped? -- Robert

RAY: Hmm. He may have had a boat payment due, Robert.

TOM: Exhaust temperatures are usually around 500 degrees. So 900 is high. The question is, WHY was your exhaust temperature 900 degrees? And I'm not sure the
catalytic converter had anything to do with it.

RAY: Me either. In most cases, when a converter gets plugged, the performance of the car suffers, and that's how you notice the problem.

TOM: A hot converter could be caused by an over-rich mixture (too much gasoline, not enough air), the excess of which is getting burned in the converter. It could also
be caused by retarded ignition timing, which could also cause the gas/air mixture to burn in the exhaust system rather than in the cylinders.

RAY: And if either of those problems is the case, your brand-new converter is probably running at 900 degrees now, too.

TOM: It's designed to withstand temperatures that high (and higher), but I'd still take the car to your regular mechanic, Robert, because you may have an engine
problem. A muffler shop may have such a vested interested in focusing on the exhaust system that they may not be looking at the big picture. So ask your regular
mechanic whether your converter is too hot, and if so, if he can find the cause.

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