The temperature sending unit may be weak, or the temperature gauge is faulty, and gives a false reading. Have your mechanic check the temperature sending unit, and see if it is working properly. also have him check the engine coolant level, and make sure the antifreeze is clean and not dirty or weak, that will sometimes cause a slight temperature rise if you are driving in bumper to bumper traffic, in warm climates...Check the radiator hoses for wear, if they are too soft, or bloated at the clamp areas, replace them. also, see if the lower return hose is collapsed,when the engine speed is increased, that will cause a temperature spike, or hot spots in the cooling system.