My Mom's '83 Reliant overheated when I left it idling in the garage on a 50 degree day with the garage door up. We replaced the water pump and the radiator cap. I noticed that the fan did not come on, so I checked the electric fan by putting 12v to it and it ran ok.I also removed the connector to the electric fan switch and, when I shorted it across, the fan came on. I thought that the fan switch in the radiator was probably bad, so I then replaced it. When I did, I was surprised that no coolant came out of the radiator. Was this normal? When I started the car, it eventually overheated, again without the fan coming on. I then removed the new fan switch and, to mysurprise,was greeted by a rush of hot coolant. Did this mean than some sort of crud had been sealing the coolant from contacting the sensor? I then ran the engine again, and was pleased when the fan came on, and the engine continued to run without overheating. I had been adding some Sea Foam to the carburetor, because there was some backfiring through the carburetor (see previous thread), so I let the car sit for about 15 minutes. When I restarted the engine, to my dismay, the fan failed to come on, and the engine light eventually came on (but no coolant went into the reservoir, which was cool).

What is the most likely cause of the failure of the fan to sometimes come on? I know that sometimes electric motors can have "dead spots", where they will not come on, but if they stop at another spot, they may start without any problem. Any ideas?

TIA, Brady

 

Update to my post, if anyone is interested. I pulled the connector off of the thermal sensor and shorted it across with a piece of a paper clip. The electric fan came on everytime that I turned on the switch, so it appeared that the fan relay and fan motor were working properly. I replaced the radiator with a new one, because it appeared that the old one was clogged beyond repair. Afterwards, the car did not overheat, even after idling for about 20-30 minutes and the fan did come on. I would not have suspected that the radiator could be so clogged up that the thermal sensor would not heat up enough to operate the fan.

Brady