So I visited a fellow who was parting an LS400 - had to get some odds and ends for my car. The car he was parting, he bought for dirt cheap because it did not run at all and was making horrible noise if you tried to start it. But mileage was relatively low (around 130k if I remember correctly) and it looked to be in a good shape. However, I noticed that most parts that needed to be changed were not changed, so it was not maintained or looked after properly

Anyhow, the mechanic who was parting it told me that the noise was actually coming from the catalytic converters - they were completely broken into pieces. He first thought of fixing the car, but later changed his mind and just parted it out. When I asked him what he thought caused the cats to explode like that, he said that he saw that happen when people were running bad gas in their car - like too low octane, or low octane + junk gas (water or dirt in it)... I know it sounds strange, but this mechanic really knew his stuff - he was not your average grease monkey.

So, it seems that it is much better to run recommended gas in our cars. Either that, or something else caused the trouble, but I am tempted to believe that low octane gas could not have helped.

 

there are many other contributors to the cats failing, and i find it very hard to believe the main culprit is bad gas. it could be a combination of neglect then bad gas.

certainly you should be running the right recommended octane to prevent knocking and unwanted ignition timing changes. we ALL should be running at a minimum of 91 octane!

 

I use 99 RON in mine

 

Most likely. Also, when you think about it, for cats to explode, they have to be completely clogged up with soot (what else?), and that happens when fuel is not burning properly... so whatever caused that condition in the first place and produced excessive amount of smoke, caused his cats to fail like that.

 

9/10 cat issues are caused by ignition or timing problems, cat's can get sooty and still work. But if you dump raw fuel into them they are toast, melty, melty toast.

 

The only bad gas that can hurt them is old leaded gas. Also zinc rich oil will do it too. I agree with the too rich deal, and it could be from the low rider syndrome too, scraping them all over the bumps etc. Any kind of impacts to the exhaust system could damage them. Maybe even running a hot cat into deep water may do damage.
It the old gas or cheap gas as you say burns okay in the engine, there is nothing special that is going to ruin them. I would bet on physical damage on a low mile car.

 

Never thought about that one - but makes perfect sense because sudden change in temperature could easily crack them

 

Additionally - failing ECM could have been dumping fuel and burning up the cats.

That said I think bad fuel is worse for the bearings/pistons than the cats. Mine knocks and pings under heavy load with anything less than 91. Due to the crazy amount of sound deadening you won't even hear it unless you're going up a hill with the windows down and a wall next to you.