What would cause a catalytic converter to melt

An engine that is not performing properly, that is not burning all the fuel, will allow unburned or excess fuel to enter the exhaust system. When this excess or unburned fuel contacts the hot core of the converter it will ignite. This constant infusion of unburned fuel will cause temperatures to continuously rise above the designed operating temperature until the core of the catalytic converter will actually melt.

Possible causes for the excess fuel entering the exhaust system are an incorrect fuel mixture, incorrect timing, corroded spark plugs, worn and cracked ignition wires, improper fuel pressure, a faulty oxygen sensor, sticking float, faulty fuel injector or a malfunctioning check valve.

Oil or Antifreeze Entering Exhaust When oil or antifreeze enters the exhaust system and contacts the hot core of the converter the oil and antifreeze will burn off leaving carbon deposits. The carbon deposits will coat the core of the converter thus reducing the catalytic converter's ability to convert from harmful emissions into harmless compounds. But where do you think all that crud goes? As soon as it clears the exhaust manifold it goes right into the cells of the honeycomb brick.

People complain that catalytic converter manufacturers routinely deny their warranty claims. They examine every converter returned under warranty. They check for impact damage on the case. They look for metal discoloration that would indicate overheating.

Overheated metal appears grey and shows signs of rust. They look for plugged cells in the honeycomb brick—yes, your engine problem caused the catalytic converter to plug up. They cut the converter apart and test for coolant, oil, and silicone contamination. They also check the condition of the matting to see if it shows any sign of impact damage.

They include wiring diagrams and technical service bulletins. In most cases, their diagrams are right from the factory manuals. Unburned fuel is entering the catalytic converter and then burning, creating intense heat. The most likely cause for a clogged or damaged catalytic converter substrate is excess unburned fuel in the exhaust. Misfire: Anything that causes a misfire or excess hydrocarbon HC in the exhaust will result in catalytic converter overheating.

Photo courtesy of Wikimedia Commons. Know How. Having been bitten by the car bug at a young age, I spent my formative years surrounded by Studebakers at car shows across Quebec and the northeastern United States. Over ten years of racing, restoring, and obsessing over automobiles lead me to balance science writing and automotive journalism full time.

I currently contribute as an editor to several online and print automotive publications, and I also write and consult for the pharmaceutical and medical device industry.

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