I had a similar issue with my 350 sbc - it turns out that the first problem was a misread on the gauge. The sensor is screwed into a reducer fitting that is in the head between the number 1 and 3 cylinder. It seems that when they wired my car and installed new gauges, they did not seat the sensor far enough into the reducer; thereby, it was reading head temperature next to the headers and not the water temperature in the water cavity. After I seated it, the temp now reads 190 instead of 230. It still runs hotter than I would like with the air cond on; however, I am going to install a pusher fan out front to help bring down the condenser temp as well as the radiator temp. I don't know much about this whole cooling thing except that sometimes one makes false assumptions about the problem and it turns out that it is a whole different issue.