I'm running a 160 thermostat and my old 216 stays under 180 in all driving/idleing conditions. I also leave approx1 1/2 - 2" of air space in the radiator.
I just recently got the heater operational and even tho my tests was when ambient temps were around 70, the heater ran me out of the cab. As been said you might try a 160 thermostat to see if that lowers your temps.
Good luck
Dave
