I have a 2003 S10 pick up with a code light for a thermostat, guy at the auto parts store said it does it all the time when weather changes. But, it has come on for the 3rd time. Should the thermostat be replaced?

Thermostat or engine coolant temp sensor?

The code reader was from OReilly Auto Parts, it was a generalization. I did see on the screen it said thermostat. Will check again tomorrow for exact wording, if you think it is necessary.