I used to add the regular old fashion green coolant to the radiator and had over heating problems, 

had the radiator serviced and cleaned, new thermostat etc. but when sitting idle in traffic it would still rise near boiling point.

I also have two electric thermo cooling fans which do help a lot.

I found a product on the net called Water Wetter, flushed the system and amazing, engine runs much cooler

and no problem since. I discovered also that anti freeze anti boil/corrosien inhibitor increases heat in radiators.

I have used it twice for the past 5 years, radiator still very clean and running up to 90 Cel.

Here is the link to a vast superior product around $40. Redline Water Wetter; details

www.raceindustries.com