coolant temperature switch turns on the fan, if the fan isn't running the car's overheating...it's a sensor mounted in the coolant line that detects coolant temp.
it is possible your radiator is clogged
It probley has an AIR pocket in the cooling system. Bleed the air out of the system and make sure it is full of fluid.
Check the thermostat or the radiator. The thermostat could be sticking or the radiator could be plugged.
I had replaced the water pump and radiator. This had continued to overheat but not as bad. After replacing the head gasket it was finally fixed. I was able to answer my own question only after replacement.
first , the thermostat could be stuck. try replacing it. if your radiator OS losing coolant, there may be a leak in the radiator causing it to overheat, or the water pump could be bad. thermostat is the likely cause if it is not losing water.
Bad thermostat, cap and radiator is a common cause.
Bad radiator, gaskets, water pump, thermostat
You may need to replace the radiator thermostat and gasket.
Fixer pluged radiator or caused thermostat to stick shut.
It could be the radiator is clogged. The thermostat could be bad (prevents the coolant from circulating from radiator to engine block)
Check the fan thermostat.
One reasons a Subaru Forester may overheat is because the radiator may need replaced. Another reason could be the thermostat.