I have had an issue recently where my thermostat wasn't working, the temp gauge was always showing below 80, so ive had my thermostat and a few other bits replaced but now the temp guage gets up to 90 very nicely and sits there but after about 10 minutes it will rise and rise and get to about 110 and then depending on how fast I am going it will fluctuate between 95 and 110/115. (the faster I go the higher it goes) should I be worried the car is over heating or has my mechanic missed something?
Thanks in advance.