Engine light came on from failed thermostat now light is off and running at normal!

My engine light came on so I went to a mechanic to see what the problem was and they said I needed a new thermostat as I was running at lower temps. The light went on and off for about a week or 2 then it has stayed off for about a month now and I am running almost normal temps and it warms up fine. What should I do? Should I change it or leave it?

Do you not know how to read or somthing???

Cuz this is your 3rd thread about this same topic and we have answered all your questions thus far.