Random overheating is a weird one, and that's probably why you didn't get an answer. I would work to correctly diagnose the problem. It could be anything from the water pump to the reservoir cap.
The first thing you need to do is note when the car is overheating- especially if it is overheating while you're moving at speeds higher than 30 mph. Low speed overheating is usually due to either the fan resistor or the fan motors- you already know. Use the electronic odometer trick to monitor the temp that the sensor is actually reporting. This is also helpful in diagnosing an improperly functioning temp sensor. Key off, press and hold the odo reset button, turn the key on, hold the reset button until the odometer reads [test]. Now each time you press and release the odo reset button you'll scroll through one of 30 test functions. You're looking for the one that looks like this [55 C] or whatever your ambient temp should be if the car has cooled overnight. Yes it's in C, so you'll have to familiarize yourself with C-F conversion. If the temp sensor is bad, you'll see ridiculous jumps in engine temp like from 100C to 200C. An infrared thermometer is also helpful in diagnosing a bad temp sensor because you can measure the temp of the radiator hoses to see if the sensor is reading incorrectly. The hoses should read within 10 degrees F of the temp sensor. You can also monitor the thermostat operation when the car is cold. The thermostat should open around 95C, and then you'll see the temp drop to 80ish and then climb back up.
IIRC, low speed fan temp is some ridiculously high temp like 116C, then high speed is shortly afterwards around 118C.
If the car is overheating while driving at speeds higher than 30, you might be looking at a bad water pump. One way to tell if you have a bad water pump is to grip the lower radiator hose to see if you can feel coolant flowing through the hose.
To check for a leaky radiator cap, find the end of the overflow and stuff a piece of paper towel in there. If the cap is leaking, it will cause coolant to shoot out through the overflow, and that will force that paper towel out of the hose. In this case you'd be losing coolant with each drive, and each time it overheats. The reason that causes overheating is because the cooling system must maintain pressure in order to do it's job. If it loses pressure, the coolant boils over. Small leaks like pin holes don't decrease pressure rapidly enough in most cases to cause overheating like this, but a bad cap will because it opens the overflow.
Good luck, I hope you figure it out, and it's something simple like a bad temp sensor.
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