My Engine is Overheating

I would replace the switch and check out the wiring harness for starters.

Best suspect is a leaking cylinder head gasket. Your mechanic can perform a chemical test at the reservoir to verify that. The test involves drawing air from the reservoir, while the engine is running, through a glass cylinder with two chambers partially-filled with a special dark blue liquid. If combustion gases are present, the liquid will turn bright yellow.

Those gases can pool under the thermostat and cause it to not open. Thermostats must be hit with hot liquid to open. Hot air will not do it. The engine will overheat when the thermostat does not open, and the pressure in the cooling system will force coolant into the reservoir.