[brucepick]

RandomFact314, I think by this point you've maybe got this information sorted out, but from your first posts here it looked like some clarification might be in order. Sorry that a lot of what's below is sorta off topic but - if you're going to discuss modifications to the cooling system these basics need to be in your head first. In my humble opinion, of course.

The radiator is passive. Water (coolant) goes through it and and air passes over the fins, which cools the water. If there's absolutely no air flow (or no water flow), the water isn't cooled. Exactly how much cooling occurs depends mostly on air temperature and air flow speed.

The thermostat is also passive. In fact it's mechanical. When t'stat is cold it is fully closed, and water circulates through the engine and pump in a loop. Water flows through it and when it reaches a set temp the t'stat valve opens slightly, allowing some water to flow to the radiator. As the water gets warmer the t'stat gradually opens up further allowing more % flow to the radiator till it reaches a temp (maybe around 200-205 deg. F) where it's allowing full flow to the radiator, as much as it can open up the valve. Boiling is 212 deg. F so it's fully open before that point. Also, the cooling system is sealed so the boiling point is actually a bit higher than 212.

Under most conditions the t'stat and road speed airflow over the radiator are enough to keep the engine from getting too hot. Lengthy idling, heavy stop and go driving, or brutally hot days with a/c combined with idling or stop+go, can can set up conditions where the engine isn't sufficiently cooled. Enter the radiator fan. The fan increases air flow over the radiator fins so as long as everything else is in good working order, this will increase cooling capacity.

Assuming a 'modern' computer controlled car, the 'puter monitors the coolant temp and will start the (electric) radiator fan if coolant temp rises to some set limit. In my car it seems to kick in around 206 deg. F, which I can track on the ScanGauge.

Earlier cars, especially rear drive cars with in-line engines, had a mechanical fan run off engine belt pulleys, located right behind the radiator. Instead of computer controlled switching, it had a mechanical thermostat that increased the speed of the fan when the coolant got too hot. Otherwise the fan was nearly freewheeling; with the engine off you could spin it by hand.