cats last the life of the car unless there is an issue AND THE VEHICLE CONTINUES TO BE DRIVEN WITH SAID ISSUE!!!!!!
while you may have been a mechanic most of your life you likely are stuck in the old train of thought. an engine needs restriction to work properly, gutting a cat can only help becuase its too much of a restriction, and my personal favorite.....cats are a replacement item.
my mazda has 230k miles on the original cat. ive seen 97+ f150s come into the shop with 300k and no problems to the cat. the ONLY times ive seen a failed cat was due to impact damage or a problem where raw fuel was allowed into the exhaust for whatever reason and the vehicle continued to be driven.
True again. The vehicle must be driven with said issues. Case in point: I have a 1994 Explorer Sport 2WD with the 4.0L pushrod V-6 and 5-speed transmission. When it reached about 120k miles, the engine started using about a quart and a half of oil between changes. There were no leaks, no smoke, no knocks, no check engine light. Nothing that would indicate that there was a problem. Because of my limited budget, all I could do at the time was put it on a diagnostic computer to see if there was a problem. No codes came up. I kept an eye on it for a while and just added a quart of oil every once in a while between changes. It finally started running hot and losing power. It finally blew a radiator hose while my wife was driving it, overheated, and cracked both heads. After I replaced the heads, head gaskets, intake manifold gaskets, thermostat, and belts and hoses, it continued to run hot and sluggish. But it wasn't using oil anymore. It turned out that the valve stem seals on two of the six cylinders were deteriorated and letting oil leak into the cylinders. The reason there was no smoke was because the catalytic converters were absorbing and converting the large carbon molecules from the burnt oil, something they were not designed to do. The reason the engine was running hot and getting sluggish was due to the raw burnt oil clogging up the converters, causing excess back pressure. It continued to run hot and sluggish after the head incident. I gutted both converters and have had zero problems since. It has more power and gets better gas mileage than it ever did before. Point is, it is not just a rich fuel mixture that can clog cats. Oversaturation due to burning oil can and will stop up a converter in no time. And most people don't realize the oil is burning because there will be no smoke.
And yes, engines need a certain amount of restriction in the exhaust to be street driveable. However, mufflers did a fine job before catalytic converters came along. And catalytic converters are for emissions control, not sound deadening or back pressure. If you gut or cut off your converters, you may need to install more restrictive (read "quieter") mufflers to make up the difference. But only if there is a noticeable drop in performance, which I haven't seen as of yet.
If your engine runs perfectly for hundreds of thousands of miles and you have no issues, yay for you. You've got a great car. But for the majority, there will be some issues. And a lot of people (like me) can't afford to spend the kind of money that new catalitic converters cost. And there are many factors that can cause a converter to clog. That's why in the 1970's and early 1980's, most cats were composed of ceramic beads coated with palladium and platinum. On these cats, there was a plug at the bottom that could be removed, allowing the beads to be emptied and replaced "when" the cat became clogged. The newer porous ceramic brick is more durable and less prone to clogging, but it still happens.
My Mark VIII runs better, has more power, and gets better gas mileage now than it did when I first bought it six years ago now that the cats are hollow. I like it. And it worked for me. That does not mean it will work for everybody. And with the MIL eliminators, there is no CEL. Nice.
