Nissan Repair: Engine overheating, nissan 240sx, coolant level

Question
I have a 1995 Nissan 240SX with manual transmission and am experiencing sporadic overheating. I have replaced the thermostat but the problem persists. The car will be fine for several days but will suddenly get very hot. The temperature begins to decrease almost immediately and returns to near normal in a few minutes. There doesn't appear to be any significant decrease in coolant level.I suspect that the problem may be related to the cooling fan although it seems to be working okay when the car is idleing.I am afraid that if I take the car into a shop they will not be able to observe or diagnose the problem. Any thoughts or suggestions will be appreciated.

Thanks,

S. Smith  

Answer
Sheldon,

I did one of these and it was a headgasket.  But, the head gasket blew because the converter was melted shut.  So, I did the headgasket and then changed the converter.  But, it gets worse...  The converter melted the wiring under the seat and the windows and they stopped working.  So, first check the converter to see if it is plugged.  Basically, look under the car when the car is as hot as you say it gets and see if the converter is glowing orange.  If it is replace it.  Second check the radiator for exhaust gas.  You can buy the kit from the store that will tell you if the exhaust is getting in the antifreeze.  If it is, replace the headgasket.  You can feel under the seat and see if the carpet is crisp and this will tell you if there was excessive heat.