Why are we discussing this, fix the plugged radiator, and then do what you have to to get the car running at thermostat temperature. The OP asked how to get the car to run cooler. Fix problems and make mechanical and programming changes if needed. (Fan settings and thermostat change, and maybe radiator change)

 

I'm seeing some confused ideas about what the thermostat does. The thermostat establishes and maintains the minimum operating temperature. Until it opens the radiator and fans are out of play and this allows the engine to hit the thermostat temperature (or thereabouts). Once the thermostat opens the radiator begins doing it's job, and when the temp rises to the fan switch temp the fan(s) kick on to help. Once open, the thermostat has done all that it can to aid in cooling by allowing the things that actually do the cooling come into play.

That said, the lower the temperature thermostat you install the sooner the radiator begins to help with cooling. There is such a thing as too cool, and this is why you should run a thermostat on a street car.

I lost the original radiator last fall and when I removed it it looked like the one in the photo posted by Cruisinfanatic. Obviously that's going to effect how much cooling effect the radiator can accomplish. I replaced it, and this spring I also replaced the water pump because I had a leak at one of the bolts that ran through the water jacket. I was still seeing 230 - 240 in traffic on hot days, and I was still having a vapor-lock like hot re-start problem. I installed a 180 thermostat (as opposed to the stock 195 version) and a lower temperature fan switch from Corvette Central to get the cooling process started sooner in the climb from ambient temperature to wherever it tops out - which is wherever the cooling system working at 100% can limit it to. In doing so I've effectively moved the temperature range in which the car operates down by 40-50 degrees. I'm seeing operating temps in the 190s, which is plenty hot, and the hot re-start problem is solved.

 

Someone who gets it.

 

You're limited to how much heat can be removed by the radiator. The differential varies with ambient temp as well. You could run no thermostat but if the air is warm enough and the engine produces x amount of heat and the rad can only remove y amount with a given energy you'll end up running at whatever temperature that removed settles at. Heat transferred is heat transferred and nothing will change that unless you change the physical properties of the block, coolant, radiator or air. In other words, the block will transfer at a rate into the water that will transfer into the rad at a rate that the air will transfer at another rate. It is actually conductivity properties, just in this case they are the thermal ones.

Edit: increasing air flow will increase the temp drop across the radiator to a point....

 

Yes, we agree: "I installed a 180 thermostat (as opposed to the stock 195 version) and a lower temperature fan switch from Corvette Central to get the cooling process started sooner in the climb from ambient temperature to wherever it tops out - which is wherever the cooling system working at 100% can limit it to."

 

Just to be clear, my original concern was that the fans shut off when the ignition is turned off. Which I now know is normal for these cars.

I think my cooling system is working as it should but I will check the radiator for dirt etc. I'm in North Texas and the 230 plus degree temps I was seeing was during stop and go traffic for 30-40 minutes on a very hot and humid day, with the A/C running. Last Saturday morning I took the car out for a drive. It was in the low 80's, no traffic. It stayed in the 180-200 range so I think everything is fine.

Thanks for all of the input!