Why does my temperature gauge needle does not remain stationary when I'm driving

Thank you very much for your response; one last question...sounds very technical, is it better to take it to the dealership or ok to go to an authorized car center.

Most temperature senders have only one wire with one connector. Find it, tighten it up, then using a paper clip, ground it to see how your temp gauge responds. When that wire is grounded, the guage should travel to the high end of the guage range. If it does, the guage and associated wiring( circuit),is good, and the problem is a loose wire, or a faulty sending unit. I can lead you through a diagnostic routine if I you like. I know I could find it and fix it easily. It's not that difficult. More than anything, it depends on the knowledge level of the person who actually puts their hands on your car. You can go to a great shop, but if the job is assigned to a low knowledge tech, he might not know how to check it and you'll end up paying for a diagnostic fee and no solution. Better to do it yourself. I can help you.