What causes an engine to get hot

That could be the thermostat that is sticking. The catalytic converter has nothing to do with the temperature in the way that you are describing. Catalytic converters get very hot by themselves when they work correctly. If they are defective then they are either plugging up or losing their ability to convert. This would not cause the heat issue. The other thing that can cause catalytic converters to overheat is the engine running rich.

You converter is not the reason for misfire,Bad spark or leaking injector will release row fuel in converter and after burn and glow red hot. remove all spark plugs an look for one is black. or wet . replase plugs with DENSO or NGK inspect the wire for burn blue marks on the side or replace the injector if fluted cylinder.
Good luck

catalytic converter stoped up or tailpipe pluged

Could be the ignition coil or it also could be a plugged catalytic converter. The converter being plugged will show several different signs, 1>) a rotten egg smell when vehicle is off 2.) loss of power 3.) fuel mileage drop. The ignition coil could also be weak. not bad enough to overheat and shut it down but enough that when its hot and shut off that it wont allow for spark due to being hot.

A rich fuel mixture will cause the catalytic converter to run hot. A plugged catalytic converter will cause the engine to run poor but not overheat normally

If you scan the error codes what does it say? You can get this done at any autoparts store (chain) for free. However it sounds to me like there is some air restriction in the intake that is causing the loss of power and the exhuast is running rich. This causes the catalytic converter to overheat. You need to be mindful that any leaks of fluid near the catalytic converter can cause a fire and the loss of the entire vehicle when they get this hot.

There are two ways a converter can fail:

• It can become clogged.
• It can become poisoned.

There really is no "inspection port" for the consumer or mechanic to see an actual clog in a converter. Often, the only way to tell if a catalytic converter is malfunctioning (plugged) is to remove it and check the change in engine performance. When a clogged converter is suspected, some mechanics temporarily remove the O2 sensor from the exhaust pipe ahead of the catalytic converter and look for a change in performance.
A catalytic converter relies on receiving the proper mix of exhaust gases at the proper temperature. Any additives or malfunctions that cause the mixture or the temperature of the exhaust gases to change reduce the effectiveness and life of the catalytic converter. Leaded gasoline and the over-use of certain fuel additives can shorten the life of a catalytic converter.
A catalytic converter can also fail because of:

• Bad exhaust valves on the engine
• Fouled plugs causing unburned fuel to overheat the converter

­Sometimes you can tell that a converter is clogged because you don't go any faster when you push the gas pedal. Also, there usually is a noticeable drop in gas mileage associated with a clogged catalytic converter. A partially clogged converter often acts like an engine governor, limiting the actual RPMs to a fast idle. A totally clogged converter causes the engine to quit after a few minutes because of all the increased exhaust back pressure.
The catalytic converter, like the rest of the emissions system, typically has a warranty length that exceeds the term of the warranty for the rest of a typical U.S. automobile.
Here is a safety reminder: Do not park your car over tall grass or piles of dry leaves. Your car's perfectly running catalytic converter gets very hot -- enough to start fires! You can keep it running well by keeping the ignition system in top shape, to prevent any unburnt fuel from entering the catalytic converter.

Check to see if the catalytic converter is clogged, a clogged converter will cause poor performance, the engine to overheat and the exhaust to glow red hot. That should FixYa. Find a different mechanic.

Check to see if there is water in the oil...If there is water in the oil then it could have a head gasket problem...Excessive exhaust backpressure because of a clogged catalytic converter could also cause overheating..Also check belt tension and condition. A loose belt that slips may prevent the water pump from circulating coolant fast enough and/or the fan from turning fast for proper cooling...Another thing it could be is a faulty Water pump -- Any wobble in the pump shaft or seepage would call for replacement. In some instances, a pump can cause an engine to overheat if the impeller vanes are badly eroded due to corrosion or if the impeller has come loose from the shaft. The wrong pump may also cause an engine to overheat. Some engines with serpentine drive belts require a special water pump that turns in the opposite direction of those used on the same engine with ordinary V-belts... Also check the Fan -- With mechanical fans, most overheating problems are caused by a faulty fan clutch, though a missing fan shroud can reduce the fan's cooling effectiveness by as much as 50% (depending on the fan's distance from the radiator) which may be enough to cause the engine to overheat in hot weather or when working hard.

Check to see if there is water in the oil...If there is water in the oil then it could have a head gasket problem..Did you ever replace the thermostat? If it is stuck then it would also cause overheating...Excessive exhaust backpressure because of a clogged catalytic converter could also cause overheating..Also check belt tension and condition. A loose belt that slips may prevent the water pump from circulating coolant fast enough and/or the fan from turning fast for proper cooling...Another thing it could be is a faulty water pump -- Any wobble in the pump shaft or seepage would call for replacement. In some instances, a pump can cause an engine to overheat if the impeller vanes are badly eroded due to corrosion or if the impeller has come loose from the shaft. The wrong pump may also cause an engine to overheat. Some engines with serpentine drive belts require a special water pump that turns in the opposite direction of those used on the same engine with ordinary V-belts... Also check the Fan -- With mechanical fans, most overheating problems are caused by a faulty fan clutch, though a missing fan shroud can reduce the fan's cooling effectiveness by as much as 50% (depending on the fan's distance from the radiator) which may be enough to cause the engine to overheat in hot weather or when working hard.