I have a 99 Dodge Neon which recently started exhibiting some bizarre behavior. Originally I had to replace the radiator due to corrosion. So I got a new aftermarket radiator, new hoses, thermostat, replaced everything, filled her up with 50/50, ran the car until all the bubbles dissapeared, topped it off a little bit more. Car ran fine for awhile.
Now the bizzare stuff. Like clockwork the car will intermittently overheat after running (under load or just idling). 2 minutes or so after first starting the car and just normal driving the seat belt alarm will come on for about 10 seconds then go off, 3 or 4 minutes into driving the radio will "blank out" for about 4 to 6 seconds then come back on, interior and exterior lights will periodically dim, and most importantly - 10 minutes or so after having reached operating temperature (about 1/3 up on temp gauge) the car will overheat. This is not a runaway overheat condition. The temperature gauge will suddenly max out, the audible alarm will sound then after a few seconds (10 to 20) it will back down again. Then it will intermittently repeat all of the above from the seat belt alarm down to the temp maxing out again. It will continue doing this until I turn off the engine. It will repeat everything the next day after having sit overnight or just a few hours. When the temp maxes out I turn on the heat inside the car to help it shed some heat. It helps back down the temp gauge and it will fluctuate around middle then max out again for a few seconds periodically. I have checked the fan fuse (fuse ok). The fans work though I believe they may come on too late at times. I have replaced the temperature sensor/sender in the head. All coolant levels are normal. The reservoir is always half full. There is no coolant in the oil so that rules out a cracked head or head gasket. Is the computer bad? Or could it be a relay somewhere that's bad? I've spent hundreds on this car and no mechanic has able to properly diagnose this problem so far. Anybody have any ideas?? Thanks in advance.