Mike,
I too have thought about that, and I think that the laws of thermodynamics support what you say. Another way to look at it is: If you push the water through the radiator twice as fast, each gallon that goes through looses half as much heat, but there are twice as many gallons going through in that same amount of time, each one of them loosing half the heat. So the end result is the same. Same thing in reverse in the engine.
I do think, though that there may be a difference in HOW it cools the block due to the fact that the Model A doesn't have a bypass to circulate water when a thermostat is closed or partially closed. With a closed thermostat, the water leaving the engine is kept at the desired temperature, but the water in the radiator cools a lot (because it is traveling slowly), and therefore enters the block at a low temperature. The water in the head may be hot, but the water in the cylinder jacket can be much cooler. With the thermostat open (or no thermostat) the water flow is faster, doesn't cool so much in the radiator, and enters the bottom of the engine at a higher temperature. I've done some testing, and found that with a marginal radiator and no thermostat, there was only a 10 degree difference between the water entering and leaving the radiator, which also means that the water entering the engine was only 10 degrees cooler than that leaving. With a better cooling radiator (and a thermostat to maintain the same engine temperature), the temperature difference was more like 40 degrees. So, the bottom of the cylinder water jacket was running about 150 degrees while the head was 190. Modern engines avoid that by having a bypass to recirculate the hot water when the thermostat is closed. Does that temperature difference matter? I don't know. Model Ts always have that kind of temperature difference because of the 100% thermosiphon, and they don't seem to mind. It does seem clear though that faster water flow results in more even temperature throughout the engine as Tom suggested, but in cold weather, going without a thermostat would give more even temps, but way to cold. Using a thermostat would give higher temperature in the top of the engine, but lower temperature in the bottom where that very well cooled radiator water enters. It seems that a super-cooling 10 fin, flat tube radiator that could keep it cool in the summer desert heat would not be the best in cool weather where a radiator that looses less heat would result in less frigid water entering the engine. I guess the obvious solution would be to cover the radiator in cold weather. Or add a bypass with a valve that could be opened in cool weather. Or just do nothing and enjoy the car. It's gotten by just fine for 80 years. This may all just be an academic exercise, but it's fun to think about this stuff.
