Cleaning the cats

[NikFu S.]

and the pre-catalytic converters.

I never knew they became "clogged" and encrusted with carbon, but it makes sense.

Do these things unbolt or do they have to be cut out?
I just want to open them up dump out whatever dirt is in there and make em shiny again.

How exactly do these things work? Is this like one of those 60k mile tune up things the dealer would do but not tell you about? Is this common knowledge?

[Beav]

They cannot be cleaned.

[NikFu S.]

Originally Posted by Beav

They cannot be cleaned.

So I just need to replace them when they are really old or just leave them alone?

[Beav]

Basically. You can't fix something that isn't broken.

[shelfy]

we occasionally dip ours in teh hot tub.

[UberRoo]

They can become fouled and will definitely affect power. (It feels like driving around with your parking brake on.) They don't usually become fouled unless there's something wrong with your engine, such as excessive oil consumption. The cats have a catalytic element inside that looks like a very fine honeycomb. The little holes become plugged and the exhaust can't get out fast enough. The only solution is to replace it or break out the element. The element is quite strong, but brittle. It requires a fair bit of effort to chisel it out. I suppose you could get a really tiny pipe brush (or a length of piano wire) and brush out all of the little holes, but the elements are often kinda hard to reach.

Because they're pretty expensive, you'd know if your dealer replaced one. They're expected to last the life of the vehicle. They don't look clean even when they're almost new. Not much light passes through them, dirty or clean, so the only way to tell if one is bad, is to remove it and see if there's a dramatic increase in power. If you have to pass an emissions test, pray that there's nothing wrong with it.

[Beav]

Originally Posted by UberRoo

They can become fouled and will definitely affect power. (It feels like driving around with your parking brake on.) They don't usually become fouled unless there's something wrong with your engine, such as excessive oil consumption. The cats have a catalytic element inside that looks like a very fine honeycomb. The little holes become plugged and the exhaust can't get out fast enough. The only solution is to replace it or break out the element. The element is quite strong, but brittle. It requires a fair bit of effort to chisel it out. I suppose you could get a really tiny pipe brush (or a length of piano wire) and brush out all of the little holes, but the elements are often kinda hard to reach.

Because they're pretty expensive, you'd know if your dealer replaced one. They're expected to last the life of the vehicle. They don't look clean even when they're almost new. Not much light passes through them, dirty or clean, so the only way to tell if one is bad, is to remove it and see if there's a dramatic increase in power. If you have to pass an emissions test, pray that there's nothing wrong with it.

The only way they can become fouled is with a sudden and extremely heavy amount of oil, such that they couldn't burn it normally. Too much fuel results in them melting, thereby creating a solid mass and restricting flow.

Cleaning them with a wire, etc. would scrape the rare metal coating and render them useless. (I read in an industry rag years ago the primary catalyst was rodium, at that time about $167,000/oz. That makes for a pretty thin coating.)

Like I stated earlier, if your car is running as it is supposed to the cats really don't do much. Given that most I/M inspections are pretty lenient (relatively) most cars pass, even with gutted cats.

The easiest way to check is by measuring back pressure. Either remove an O2 sensor or drill a small hole (a small self-tapping screw will close it back up when finished) and insert a pressure gauge (like a cheap fuel pressure gauge.) Rev the engine up a bit, anything over three lbs. pressure would indicate a restriction that needs attention. To be certain it's the cat and not a collapsed pipe or muffler, repeat the test downstream of the cat.

[NikFu S.]

Well in any case I'll be replacing my main cat soon with a higher flow model. I'm pretty sure there's nothing wrong with my cats then because I don't eat up oil.