K, here's my cooling theory.
Yes, a thermostat controls a "base" temp, but if that is the only temp it allows full flow at (even when "closed" it allows fluid to flow, just not full flow) then how can your engine ever run cooler than the thermostat temp?
What I'm saying is that regardless of the ability or efficiency of your cooling system, the 195 degree thermostat is ALWAYS going to make your engine run at an min temp of 195 because it doesnt allow flow at cooler temperatures. Even if you have the worlds greatest radiator, the t-stat is gonna keep the temp at 195, make sense?
The wagoneer has a factory 193 or 195 degree t-stat. The truck would regularly run at 210 when cruising around, that is "normal" this was winter, summer, whatever. I never overheated it, but last year when it was 115 outside, i brought the temp up to 240 while pushing up a hill at 55mph, and I did not like that.
I ended up having to replace my radiator because the original one sprung a leak. At the same time I put in a 180* tstat.
After that, through the whole fall and winter and spring, the truck never touched 191 degrees. always ran right at 190ish. Not only because of the new rad and flushed system, but because the radiator was ALLOWED TO COOL to a lower temperature by the thermostat being open sooner. Make sense?
So regardless of what radiator you put in (i have a chinese ebay aluminum 3 row) the thermostat will have an effect, however so do other things. I'd check your fan clutch, that can cause overheating at idle alot, but doesnt much matter at speed. Flush your system, new coolant (mix your own), maybe replace your old thermostat with a new stock temp one if its old.
Also remember, All my experience is on a 40 year old engine thats carbureted. There's no computer no temp sensor that kicks in for this that or the other. You're before OBDII, but i'm guessing you've still got some decent computer stuff going on under the hood.
Modern engines are designed to run at specific temperatures. You'll get ****ty fuel economy and have some other issues if your engine thinks its running out of spec, but I'm not sure how much computer controled crap you have. All i know is that my computer would need to be reprogrammed if I ever changed a thermostat in my magnum, because it wants and needs to run at 210 degrees.
hope this helps?
Illegitimi Non Carborundum