318 overheating

Secret tip #1; if the coolant temperature sensor is inside an air pocket, it will lie like a dead dog. The sensor needs to be in a liquid.
Secret tip #2; If the liquid level in the rad gets to be too low, the coolant will not get into the heater core, and the fan will NOT blow hot air.
Tip #3; if the rad fins are plugged with dirt, or the condenser in front of it is, then the rad temp will march towards the same from top to bottom.
#4; a slipping belt is not always vocal about it.
#5: As for the temp spread from top to bottom, I look for about 25/30 degrees.