Wow, Mars, I didn't know you were a bona fide mechanic. Impressive.

quote:

Originally posted by wrightd:
Wow, Mars, I didn't know you were a bona fide mechanic. Impressive.

I had a thread doing the engine swap and Para's truck repair back in November.

I worked in a garage to put myself through college from 1983 to '87. I got two educations for the price of one.

I should have changed the manifold cats when I had this engine out, but was too lazy to look up inside them.

quote:

Originally posted by bcereuss:
I’m interested…and as mentioned, moderately mechanically inclined…but is that a typical 400K appearance? Should it never have made it to 400K? Is this a “never think about it for the life of the vehicle” part?

So, the shortest answer I can come up with is that this is what it looks like when too much stuff that isn’t exhaust gas and unburnt gasoline ends up coming out of the cylinder. How long it takes to get this bad depends mostly on stuff happening before the cat, rather than pure age or miles.

In a perfect world, everything that goes into the front of a cat would also be blown out the back of the cat, with some chemical changes happening along the way. However, in reality stuff that isn’t really supposed to be in the exhaust ends up in the exhaust. Primarily that means lube oil, but plain old dirt, coolant, and other stuff can end up getting into the combustion chamber, and either doesn’t get burnt, or gets turned into something that will clog or stick to the surface of all those little channels in the cat. Once they start getting clogged up, you get more uneven heating, and the ceramic matrix will start to crack and generally come apart. Now, engineers aren’t totally clueless, so most cats are bigger than they need to be to tolerate some amount of getting their little channels clogged up, but none of them will last forever. In general, the better maintained a motor is, the longer the cats will last, and 10 years or 200k miles is plenty reasonable for a cat that is on a regularly maintained engine. However, if the engine starts blowing oil past the rings, or the head gasket breaks and starts leaking coolant into the cylinders, it can drastically speed up the failure of the cats. Forgetting the air filter and sucking in lots of little bits of dust can also damage them pretty fast, but that will also cause other problems that will likely take the motor out before the cat does! Even just running too rich and dumping lots of unburnt fuel into the exhaust can cause a cat to fail more quickly.

Basically, if the engine is working like it should, the cats should be Ok. If the engine craps out, it is very possible that it hurt the cats on its way out. This is all a pretty broad generalization, and some cars have cats that never seem to die while others are known crap, but in general an engine in good working order isn’t at much risk of trashing its cats.

- Bret

Yeah, it cracked a ring on #5 cylinder and started using oil. Took three years to burn out the cats because it was only driven a mile or two every day.

Replacing the engine was more economical that rebuilding.

400,000 was a good run.