Restoring old catalytic converter's efficiency (cleaning method)

[California98Civic]

Originally Posted by Piotrsko

Unburned fuels tend to be like creosote in a wood fireplace. Otherwise how do you get clogged cats? Typical solution is to increase temperatures like a self cleaning house oven.

It is not improbable that this coating could fall off and clog a passage.

That's really interesting. I did clean the intake and exhaust passages to the extent that I could reach them when I took the head off. And I also cleaned the surfaces of two of the Pistons, those that were easy to reach. But the other two Pistons remain quite dirty. I suppose something could have flaked off there or from somewhere deep within the exhaust manifold that I couldn't reach. At any rate the PO420 code has not yet repeated.

[Taylor95]

One of my vehicles threw a P0420 code today, and started overheating about two hours later (coming home from a trip). Is this indicative of a clogged cat? I'm wondering if this procedure would also work on a clogged cat after all of the pieces have been removed.

Another related question that may have been answered: are there proper methods for disposing of the leftover mixture after the cat is cleaned?

[California98Civic]

Originally Posted by Taylor95

One of my vehicles threw a P0420 code today, and started overheating about two hours later (coming home from a trip). Is this indicative of a clogged cat? I'm wondering if this procedure would also work on a clogged cat after all of the pieces have been removed.

Another related question that may have been answered: are there proper methods for disposing of the leftover mixture after the cat is cleaned?

I disposed of my leftovers taking it with old coolant and such to our hazardous waste facility. Different states will vary.

On your core question, ... overheating is not a symptom of a P0420. However, a failing head gasket could cause an overheating situation and perhaps set off the inefficient CAT Code P0420 if the engine begins burning enough coolant and oil. It's also possible that the two events are completely unrelated. I would start by investigating the cause of the overheating.

[Taylor95]

That would be quite the coincidence for the events to happen on the same trip but be unrelated. Possible though.

The headgasket can be ruled out because that was replaced around 20k miles ago. If the overheating is caused by the cooling system, then it has to be either a closed thermostat or failed water pump.

I'm not meaning to take the thread off topic. If my cat is also bad then I will likely try this cleaning method

[Xist]

Who replaced the head gasket? If it was someone like me, I would not feel terribly surprised if it failed 20,000 miles later. If the engine is now burning coolant and\or or oil I could see that damaging the CC and the unit itself can become damaged if it overheats.

However, this guy's Chrysler's engine blew the gasket when the cat clogged: https://mechanics.stackexchange.com/...he-cat-to-plug

[Taylor95]

A shop that I trust did the job. However, the car in question is a subaru...
A clogged cat would be easy enough to diagnose once I get the car on jack stands.
I really hope the code is just because of a dirty air filter or something...

[Xist]

A mechanic told me they stopped replacing Subaru head gaskets because they kept coming back.

I just do not see a shop refusing a $1,750 job with approximately a 0% chance of failing during their 12-month, 12,000-mile warranty.

[oil pan 4]

Exhaust blockage can burn exhaust valves, blow head gaskets and crack a head. It's bad.

[California98Civic]

Originally Posted by Taylor95

A shop that I trust did the job. However, the car in question is a subaru...
A clogged cat would be easy enough to diagnose once I get the car on jack stands.
I really hope the code is just because of a dirty air filter or something...

For what it is worth, my CAT is still running strong after the cleaning. I have twice seen isolated returns of the P0420 CEL. They were months apart. Both were on long trips on a hot day. The second event was during a high mountain climb into the high desert of SoCal, under significant load fir a long duration. Each time, clearing the code with my ultra gauge did not produce a recurrence. I think this indicates that the clean is good, but the CAT does not become "new" as a result.

[jimmylomax]

Originally Posted by California98Civic

For what it is worth, my CAT is still running strong after the cleaning. I have twice seen isolated returns of the P0420 CEL. They were months apart. Both were on long trips on a hot day. The second event was during a high mountain climb into the high desert of SoCal, under significant load fir a long duration. Each time, clearing the code with my ultra gauge did not produce a recurrence. I think this indicates that the clean is good, but the CAT does not become "new" as a result.

I have a dumb question (and admit to skipping several of the middle pages of this thread - so I apologize if it's already been discussed). do you think the times the code came back may have been longer stints without EOC? I ask because sometime this summer, I got a P0420 in the Fit on a long commute where I left the AC running for a passenger. I cleared it and it has since come back a couple times when I went longer than about 15m between EOCs. Did you run an OBDII scanner and look at the O2 sensor data or measure pre and post cat temperatures? (I've got 30 days to make mine happy to pass my local DOT inspection).