Thanks for the correction, Pat. Somewhere along the line, years ago, I was led to believe that the ceramic was zirconia (zirconium oxide). Maybe it was in the early days, or maybe I was just misinformed.
Anyway, checking around, I see that they use cordierite, a magnesium-aluminum silicate with a low melting temperature for ceramics, very close to that of stainless steel. In a thin-walled honeycomb, which is the substrate for most cats today, I don't doubt it would melt before the outside can does.
So, Harold, ignore what I said, and thanks to Pat for correcting me.
On Thu, 14 Oct 2004 14:35:09 GMT, "Ed Huntress" calmly ranted:
-snip-
Just posted to the dropbox: meltedFordCat.jpg
Back in the late 70's, I worked for Dixon Ford in Vista, CA. A client brought in a vehicle which he said would not tune up, and he'd taken it to half a dozen places.
I noticed a hiss from the exhaust when I tried to rev the engine and that led me to the gas filler, whose small "Unleaded Only" diameter adapter plate had been less than cleanly opened up. I was surprised that he didn't blow himself up with the sparks from that chiseling. The owner told me that he was on his third tank of leaded gas.
I tracked the problem down to the catalytic converter being plugged, and once the new one was installed, I cut the old one open to see how the plug had come about.
Attached is a picture of both good honeycomb catalytic element and one piece from the front after the leaded gas. It got quite hot, as you can see. I believe the metallic structure of the honeycomb stayed intact, though.
On the left, the output section; on the right, the plugged input. It appears that the fuel additives danced on top of the hot converter until they coagulated and melted, plugging up the front of the honeycomb and cooling it at that point.
About 3/4 of the input was plugged like this.
It took 3 weeks to get a new filler neck for him, too.
------------------------------------------- Stain and Poly are their own punishment
FWIW, the zirconia issue bugged me enough to track down where I got it, and I see that it's *oxygen sensors* that use zirconia substrates, not catalytic converters. Zirconia's melting point is in the neighborhood of 4,400 deg. F, versus 2,500 F for cordierite.
That's a lesson to check facts (which I always do in print, but not always in a NG), and a relief to me that my memory is only half-shot.
Well i will find out if this guy used any fuel additives.Thats a good place to start I do not have any pic.We shure do not want to foul up a new converter ! I will find out if he got gas at a new place. Thank you for the constructive input. Harold
Actually, the ceramic DOES melt - And it doesn't necessarily take out the car (or even the "can" of the converter) when it happens. The cat I had to get replaced on my car last year is a prime example - Severe blockage diagnosed. Zero visible damage externally - The can showed no particular sign it had even gotten particularly warm. Cut the old one off, put the new one on, and had the guy split the old one. About 3/4 of the catalyst matrix (looked like it was originally a honeycomb type design, much like the heating elements in one of those Pelonis ceramic disc space heaters) had melted and slumped into a fused mass.
On Thu, 14 Oct 2004 15:49:15 GMT, Johan calmly ranted:
But not hot enough to melt the honeycomb structure. All the molten crap was on top which tells me that the comb must have been SMOKIN' for it to repel the additives like that. My guess is that the coagulation slowed the flow through the comb in that area to cool it enough to allow the deposition to stick to the comb. (That was a mouthful.)
- Don't be a possum on the Information Superhighway of life. ----
They can and do melt inside. Not during normal operation, but if you have an exceedingly rich condition and then somehow ignite the mixture in the cat, it will melt/constrict them. I had this happen to a car a few years back. Talking to a GM engineer who worked in emissions, I was describing the symptoms(low power, bad mileage, etc) and he said "sounds like the cat is all plugged up" He explained to me how it happened.
I changed the cat out and sure enough all of the problems went away. I then corrected the rich mix problem and the car ran fine after that.
Ok, Dealers want an arm and 2 legs, but where to get a cat? I have a check engine light that when run through the scanner says it is a slightly plugged cat. (car so far shows no signs of drivability trouble) Dealer quoted a price that gave my wallet shudders, but when I went to the auto parts stores I was told that it is presently only a dealer item because the car (a 1999 Honda Odyssey) is only 5 years old and the goverment makes the manufaturers warrent the cat's for 5 years. (anyway, that's the story I got) I thought of getting one from the junk yard, but haven't tried yet because someone said that it is illegal for them to sell you an used cat. Car has 174,000 on it already and I really don't want to spend a large amount of money on it. Won't pass inspection in Feb with the Ck.eng.light on. Suggestions? can I use a cat from a dead ford van that I still have?
|| ||Ok, Dealers want an arm and 2 legs, but where to get a cat? I have a check ||engine light that when run through the scanner says it is a slightly plugged ||cat. (car so far shows no signs of drivability trouble) Dealer quoted a price ||that gave my wallet shudders, but when I went to the auto parts stores I was ||told that it is presently only a dealer item because the car (a 1999 Honda ||Odyssey) is only 5 years old and the goverment makes the manufaturers warrent ||the cat's for 5 years. (anyway, that's the story I got) I thought of getting ||one from the junk yard, but haven't tried yet because someone said that it is ||illegal for them to sell you an used cat. Car has 174,000 on it already and I ||really don't want to spend a large amount of money on it. Won't pass ||inspection in Feb with the Ck.eng.light on. Suggestions? can I use a cat from ||a dead ford van that I still have?
As long as it's the correct type - 2-way, 3-way etc - and has a capacity suited to the engine it should be fine. You can get a universal cat through any parts store, or a muffler shop can install one for you. Texas Parts Guy
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