The fans, if running properly, will kick on when any climate system is engaged (AC or heat). Or, as Boosty mentioned @ 216 and 228. I have been running a 180T stat for a while now and it seems to keep the temps down without detriment to MPG or performance.
If you keep the DEX make sure that you bleed all the air from the system after the Tstat swap. Air can cause acidic oxidation of OAT coolants..(which could cause the early failure of engine gaskets and other nylon/plastic parts) .just an FYI.
I know that there used to be a TECHINFO article that gave great info on drilling a small hole in the flange of the TSTAT to help bleed the air, in conjunction with the bleed valve on the "water neck" (as you called it). Unfortunately, this is a newer format for the forum..and I dont know where that is anymore..
Hopefully a Mod can get in here and add a link to the TECHINFO article.
Good luck and keep us posted...