I have (had) my base timing set at 8 degrees. It is also programmed into the chip that way. I took my car to get it smogged and it passed, no problems. However as our weather has gotten hot 100+, I began to notice an overheating tendancy at idle. I had my radiator recored and that took care of a lot of it. At least I stay under 232 for now. My fans are set to come on at 180 along with a lower temp primary coolant fan sensor switch in the block and 180-thermostat. Fans are working correctly, blocks not plugged, new Stewart pump too.
Anyway the 232 still makes me uncomfortable and through trouble shooting I noticed my timing was set at 3 degrees. Smog guy must have done this. I put it back to 8 do you think this is enough retard to cause the heating on hot days on idle only? I'm still thinking it's airflow because as soon as I get moving it comes right down.
GW

 

Mine is set at 8° right now. During 95° days, it still doesn't get hotter than 190°F with the air on.

Coolant flush perhaps? It's hard to say how long you're stuck in traffic for. If it's for 10 minutes of constant stop and go, I could see the temps hovering up around 220 or so.