Truck is running fine. There was a rattle coming from the catalytic converter. I take it off and it is melted and broken up inside. It is a magnaflow that I got new 18 months ago. What would cause this? Thanks

 

Could be running really lean, i.e. vacuum leak, I had a V6 with a serious intake/vac leak that made the cat glow red hot. Could be leaking oil into the cat and causing it to be getting hot enough to melt? Or I would say cut the cat out, but you are in Cali so probably not!

 

actually, a rich condition is what causes the cat to melt... vacuum leaks cause unmetered air to go into the engine and it fools the O2 sensor which causes the ECU to add more fuel than is needed

a usual case is when there's a misfire and raw fuel is just dumping straight out into the exhaust and collecting in the cat... which is what makes it overheat

if everything is fine though, it could just simply be a defective cat... many aftermarket cats aren't as well built and don't last long because of that