got overheated the other day

Have your mechanic check for a leaking cylinder head gasket. The test for that involves what I call the "sniffer" test. Air from the radiator is drawn through a glass cylinder with two chambers partially filled with a special dark blue liquid. If combustion gases are getting into the cooling system, the liquid will turn bright yellow. Thermostats open in response to hot liquid, not hot air. Air leaking into the cooling system can pool under the thermostat and cause it to not open resulting in overheating.