I am passing on a comment made to me by a muffler/exhaust repair shop. I am not qualified to justify the validity of their advice, but it may be worthwhile putting this one in your own memory bank and checking for yourself when next talking to an exhaust mechanic.

The internal component of a catalytic convertor on your exhaust system is made up of a 'honeycomb' of small tubes. Overtime these will gradually burn out and the 'cat' will need to be replaced. Not a cheap excercise.

I was shown a 'dead cat' that had holes burnt through the core. It had a decent milage on it. This vehicle used non-supermarket budget fuels.

I was also shown a 'dead cat' that was completely melted inside and destroyed. It had about half the mileage of the other 'cat'. This vehicle used supermarket budget fuels. It seems that these fuels have a larger exhaust 'residue' which build up, clog the tubes and cause internal heat build up.

By choice I now avoid the budget fuels. Others may like to investigate this for themselves.

We all are concerned about fuel consumption, but it may be false economy to save on the trip only to have to pay for it later.

I look forward to any positive feedback.

Pete

This has been an issue for years, burnt out cats are common but rarely diagnosed correctly.

I agree with Dunaruna, a inlaw had a complete motor rebuild because of a bad diagnosis, it was the catalytic convertor. motor would run cool when at speed but got hot in traffic.

Had customers cars towd in engine wont start Cat totaly blocked. Or vehicle wouldnt go over 100Kh partly blocked (was a police vehicle ) complaint couldnt catch anyone. None of these were budget fuels.

there has been scare mungering about the cheaper fuels since they started, our 96 VS commodore has 320,000km on the clock has mostly (about 95%) run on the "cheap supermarket fuels" and has never missed a beat, and still has the original "cat" on it. the "dead cat" was probably faulty to start off with.

used to sell fuel through a reputable privately owned servo as a uni student. The delivery truck did the same run each fortnight - once our tanks were filled he'd head to the supermarket in the next town and fill their tanks. Same tanker, same fuel.
The type of fuel certainly can change the condition of an engine and/or exhaust. A car with holes in the cat (and i say holes only) won't generally be any worse off than one with a new cat. In fact, unless there are censors on the cat (which many late model vehicles have) a car will run quite well without one. You could take yours off and your car would be fine (though the $10000 EPA fine might hurt...)

What it often comes down to is the condition of the tanks at any given servo. Some don't look after their water levels in the fuel tanks well enough. Water in the fuel causes a dirty burn or misfire, which makes the cat converter work harder.
There are other ways to shorten a cat's life - but i'd have to leave that to a mechanic to describe.

The biggest cause of failure in earlier ones was when leaded fuel was still available, people would put it in either by mistake (yes, even though the nozzle didn't fit) or because they thought it would make their car go better. Depending on the quality as little as 1 tank of leaded fuel was enough to ruin the cat.

There are many other ways to wreck them though, including (but not all reasons) incorrect fuel mixture ratio (which is usually caused by faulty sensors like the 02 sensors for example), use of certain "fuel additives", leaking EGR valves, burning oil due to worn rings or valve guides, even poorly serviced cars with crook spark plugs can cause premature cat failure. Unburnt fuel getting into the cat is a big no-no, it can raise temperatures across the cat to over 500 degrees F from inlet to outlet, causing the substrate to degrade very fast.

You will also notice on later model cars the cat is now closer to the engine. The EGR setup on later cars is there to "cool" combustion temperatures to reduce NOx. NOx is produced slower in cooler combustion temperatures that has higher pressure, which is partly in conflict with the cats need for higher (around 400-600 degrees F minimum light off) and more constant temperatures for extended life and operating efficiency, that is why they are now moving them closer. This also helps give a more constant temperature across the substrate, i.e. inlet and outlet temp is closer.

Remember the old "rotten egg" smell (which is actually hydrogen sulfide) from earlier unleaded fuel cars with cats? This is caused by a "rich" air fuel ratio, which again degrades the life expectancy.

I have only scratched the surface with this and it is very very complex, moreso than just saying cheap fuel is the cause. It can be, but it may not be and usually isn't that simple.

I would not recomend just removing the cat.
The car I spoke of earlier was a VL commodore, a inlaw inherited it from his elderly mother who owned it from new, it had always been serviced at the same place, in never whent further than bingo or bowls.
when he got it he drove it to Sydney from Stawell (VIC), when he reached Sydney traffic the motor temperature whent very high, he pulled over & checked the thermo fan was working, all seemed good, same thing on the trip back to Stawell, he took the car to the people that allways serviced it, they told him he had a blown motor and it would require a rebuild.
many $$$ later the car was the same, cool at high speed & hot in traffic, the mechanics had no answers ??
He took the car to a exhaust specialist for a leak, they didn't know about his problems, they found the catalytic convertor had been gutted by the mechanic at a earlier service (before the rebuild) they rang and told him he would need a new one or his car would get hot in traffic as the heat would travel up his exhaust pipe. BINGO problem fix.
Then back to the mechanic for a full refund.
If you search the net you will find a lot of kids who hot their cars up complain about getting hot in Macas drive through, they strip out their cats looking for more power, if they only knew.

I don't want to sound like a dumbo here but my question is are catalytic converters used in vehicles with unleaded fuel only or in vehicles with diesel engines also?

Thanks,
Jeff

There was a story on TV a while back where the bush fire brigade were unhappy with their new diesel trucks as they had catalytic converters on them, they are a big fire hazard in long grass. so yes some do.