How can I tell if my Cats are getting cloged?
 

Is there a time frame when they should be changed out? My 99 has 58k on it and in the Spring it is getting new headers/exhaust. I was planning on keeping the original Cats but when it (barely) started this morning after its cold nap I watched the exhaust and it just kinda seeps out at idle. Is that normal for this car? I am used to seeing a little more of a steady flow from cars.
Thanks,
Chris

Well if you look inside it with a flash light once the exhaust is apart, the honey comb inside shouldnt have any blockage. A way i've seen my father test it on other cars is to drill a hole in the exhaust pipe before the cat and if the flow improves alot, then its likely the cat is clogged.

Thanks. Seeing as both sides are identical it is probablly normal. Never the less I am probablly going to put in the Maxflow muffler w/ cats so it will be a moot point. I think I may go with Deluboz's headers though.
Thanks!
Chris

Many exhaust shops will do this (drill a hole in front of the cats, measure with a pressure sensor to see if there is too much back pressure) and then weld the hole. It cost me $20 to do mine on a Volvo.