Catalytic converter questions.
 

My 2000 SL1 has 105000 miles on it.I am taking the time to replace parts on it as preventive maintenance as I spelled out in an earlier thread.
Now I wondering if I should replace the catalytic converter.
Do they plug up at some predictable mileage?
When getting plugged up do they slowly degrade mileage of performance?
thanks.

Naah, no way to predict when a cat con goes bad. It's not something I've ever considered a preventative maintenance item, but I'm a cheap bastard and don't like to spend money until I have to. My 99 Grand Caravan still has the OEM cat con on it and it's still in good shape. If you start to lose power while trying to pass a car or go up hills, then you may have it checked. Until then, just keep driving it.

^ what he said.

New cats often do not have the same level of plating that the factory cats have. The factory cats are expected to last the normal service life of the vehicle, a replacement cat, if needed, only has to last the remainder of that service life.

What I am trying to tell you is that a replacement cat might not last as long as the one that is in there now. You are asking for trouble. I have 265k on my original cat and no problems yet.

"If it ain't broke, you haven't fixed it enough." Red Green

Is there a way to definitively test the cat while its in the car?

The cat is constantly monitored by the computer. If it goes bad, you will get a "service engine soon" light and the code P0420. You can also get this code for other reasons so if you do get it, don't automatically assume that the cat is the reason, but it can be.

Thanks Keith. I figured I would get an SES if it failed. Is there a way to know that it is failing? Is whatever the computer is looking at available for measurement/calculation or is it just a binary thing -- either works correctly or it doesn't?

Yes, but it takes a sophisticated scanner or other equipment that the normal DIYer would not normally have. As far as the computer is concerned, its just a binary thing, but a knowledgeable mechanic will hook up a scanner that monitors the outputs of both O2 sensors at the same time, or will hook up a dual trace oscilloscope to the O2 sensors and watch their switching pattern to determine if the issue is with the cat or one of the sensors or something else.

Honestly, not a lot of mechanics out there that are capable of understanding what the traces mean or even how to use an oscilloscope or advanced scanner. Too many of them will see a P0420 and immediately jump on the cat. Then when that doesn't work, they start replacing the O2 sensors. Some will simply shotgun the system and replace everything from the exhaust manifold back.

My recommendation, cross that bridge when you come to it, if you ever come to it.

In all the years I have driving I have had two catalytic converters fail. One on a '78 Plymouth, reduced power, blowing out of exhaust manifold gasket, overheated engines and lousy gas mileage.
And my Saturn, slight reduction in power and mild over heating.
And a gravely noise when you started the car which was Catalytic converter chunks rattling.
That said, I have traded cars with 60,000 miles on them and 300,000 miles on them. The short of it. When they break, replace them, not until.

Thanks all. The car is running good so I'll leave good enough alone.