I have a 1999 ex auto civic w/ approx. 180K on it. Does the cat bolt up to the stock exhaust system or is it welded on?

Also, where could I find a replacement cheap?

Thanks,
Paul

I believe the cat is plugged intermittently.

Symtoms:

1.) overheats and VERY sluggish (every now and then)

 

You've never tried to look? It's bolted on.

Define "cheap". Because in CA it may not be feasible to buy cheap knock-offs.

 

The engine overheats and is very sluggish?

I suggest you do more diagnostics before you start tossing expensive parts at it.

Are there any CELS?

 

Bolt on unless modified, and don't go cheap on a catalytic converter. You get what you pay for.

 

This^

For example, a bad or clogged cat would not cause the engine to overheat.

 

A clogged cat can make an engine run hot.

 

Please explain how a clogged cat would cause the engine to overheat.

 

Does an air compressor get hotter if you plug one end and make it compress the air instead of just flowing it?

Exhaust is also hot. The heat is not being evacuated. It's being held in place. The new exhaust gasses may be cooler than they would be if the cylinder was filling entirely with fresh fuel....but regurgitated exhaust gasses are still hot.

Then you got the guy behind the wheel mashing the pedal trying to get it to go faster because it's bogging and not going anywhere. Adding more load causes more heat.

It's a vicious cycle.

Cars with test pipes generally run a *tiny* bit cooler. Hennesy removed the cats from one of its crazy vipers back in the day in order to get the engine to run a bit cooler.

 

I am very skeptical about this reasoning. Heat generated by compression of gases is generated whether the cat is clogged or not. I believe any increase in this type of heat would be relatively small when the cat is clogged. In fact, this heat might actually be reduced given that the clogged cat reduces engine rpms under load.

I've read this theory, but I am again very skeptical because it seems way over simplified. Hot exhaust gases unable to escape the cylinder will almost certainly reduce combustion (loss of power) and therefore reduce heat.

In my opinion, he's not going anywhere because the trapped exhaust gas in the cylinder leads to inefficient combustion and less heat. The cat was killed because the engine was already running very rich. With the cat clogged, the rich condition is likely now even worse.

This does not necessarily conversely mean that the engine will overheat due to a clogged cat.

 

It seems common sense to me...but it's also well documented that a clogged exhaust will make the car run hotter. I didn't say overheat. Maybe in extreme cases...yes...overheat as well.

 

As I explained, "common sense" turned to healthy skepticism after I considered all the factors at play.

 

You're talking about an EGR effect....which I did account for....but sonce you're plugging one end (the hot pressurized end) of an engine, it will build up heat. More load also equals more heat. Inefficiency happens because the engine is not able to inhale fresh air fuel mix and that more energy is given to pumping losses. Heat wins.

Exhaust gasses are hot. If you trap that heat...even if the fire isn't burning as hot, you're still getting pressurized heat.

Why do turbos get hot? Partially because of exhaust gas restriction.

You're backing that heat back into the combustion chamber. It doesn't matter if it's not coming out as hot. The car is still running. So it's still producing heat. You're trapping that heat.

 

Google search it. Like I said...it's well documented. FWIW...I made my post before I searched. A heat pump that can't expel its heat and is forced to compress it while being forced to move a large object.

The 4th law of thermodynamics is "it's getting hot in hurr. So take off all your clothes".

 

Would you agree that even though an engine is running inefficiently, it will continue to produce heat and build up more and more heat unless you can evacuate it?

That's how your cooling system works. By counting on inefficiency to release fuel enegy as heat instead of pure motion/work.

A clogged cat motor does take in less fuel. But it still produces net heat as long as it's running. If you can't get rid of it...does it build up? Or cool down?

 

A clogged cat is easy to diagnose. Disconnect the cat. Does that fix the problem? You might need to replace the cat.

That still doesn't answer a HUGE question: Is the CEL on? Does it work?

 

Obviously I'm not saying that it's DEFINITELY the cure to his issue. I'm just saying....clogged cats do cause cars to run hot.

 

The guy didn't know if his cat bolted on or not.....

Level of expertise: scale of 1 to 10?

He can take it somewhere and have them run a test. A vacuum gauge is probably where they'll start....if the sound of wheezing doesn't give it away.

CEL status is important and easy info however.

 

Even with a clogged cat, a significant amount of exhaust still gets released. Otherwise, the engine would stall. But I agree. There will be a little more heat built up. However, the exhaust gas build up will negatively feed back on combustion = less gasoline burned. Less gasoline burned will result in less heat.

I believe that heat does not win because this effect is largely countered by reduced combustion that reduces the potential to overheat the engine.

Partially is the operative term. The turbo is also sucking in substantially more air and therefore needing to release it. A finely tuned turbo engine is a weak comparison for a poorly running D-series with a clogged cat.

 

Lack of knowledge != lack of ability. All it takes to remove a cat is a couple wrenches, and at least one functional arm.

 

Is it well documented (supported by test results) or has it been posted and commonly repeated? If you find rigorous evidence, please post the link.

I have no doubts about thermodynamic concepts. However, I believe your thermodynamics equation for this topic may be oversimplified and incomplete.

 

Yes. But it's more complicated than this, right?

You need to acknowledge that a clogged cat reduces the exhaust flow rate but does not eliminate it. So some exhaust heat still gets released. I would argue that most still gets released. However, I believe that the net exhaust heat retention is balanced by less combustion, leading to only a small increase in heat retention that is almost never enough to cause engine overheating.

 

Sure, I'll readily say that a clogged cat reduces flow and does not completely plug it. It still doesn't change the fact that the engine is still producing a combustion cycle and hence, producing heat.

If it completely plugged it, it would stop combustion and start to cool off.

I say this after acknowledging what I'll call the "EGR effect" that I counted in on my first post.

You keep insisting that I said the word "overheat" right off the bat. I said that it will cause the car to run hotter than normal. How could it not? You're retaining more heat than you normally would. I'll even seperate out the part that the engine is working harder to keep going.

A well insulated house with a furnace that's not producing as much heat vs. a vented house with a furnace that's burning hotter.

Which house is warmer?

I hate to over simplify it. But I can't find any master's theses written about clogged cats ATM.

 

Next thing compounding it would be the retarded timing produced from low vacuum in the intake manifold.

Retarded timing and more fuel and more load are what's used to warm cars up from a cold start.

Since there is not enough oxygen for complete combustion, you might cool the chamber via fuel spray and inefficiency. But that unburned fuel may ignite in the exhaust pipe and raise EGTs. Since a coolant jacket runs around the exhaust ports, you'll be soaking in a lot of that heat as well.

Didn't 99-00 EX's have air injection as well?

 

Never seen or read where a clogged cat caused overheating in all the time I've been on this forum or owned a Honda. However, stranger things have surfaced. How would a clogged cat explain intermittent overheating? I don't recall reading that (not that I read your exchanges very closely) in the thread.

 

In my opinion, this^ is another disconnect with the bad cat-overheat theory of the OP.