This problem is normally an air flow problem but sometimes you can't get enough air pushing through the radiator because or space restrictions. I had this very same problem on my 1967 GTO 462. I added several types of expensive fans. None of this solved the problem. In these cases the solution is to give the system more volume through a bigger radiator. That can be dimensionally bigger or it can be larger tubes in the radiator. In my case, when I went to dual 1 1/4" tube aluminum radiator upgrade from a dual 1" tube unit, my overheating in traffic problem was completely eliminated. Instead of creeping up to 230 + within 20 minutes, I could sit in traffic in 90 degree temps for literally hours.
