Right having grief at the moment

my car before always used to cool down when i was driving then warm up when im in traffic and fans kick in etc as it should but recently it doesnt seem to cool itself down when im on the motorway it just stays at the same temp all the time wether im driving or stationary


does anyone have this problem or am i just beeing paranoid ???? ive spoken to a very good friend of mine and he says its ok but im just checking as im not confortable with it
Any views will be very helpful
Regards
Tony