You could do a simple test: next time you get to your destination, let the engine idle (heater off) and watch the gauge slowly climb.
Listen closely - after some minutes, the electric radiator fan will kick on. Note the temperature when it does (likely somewhere north of 200 F). The number you see on your read out is what you want to know.
You should size your partial grille block so your fan isn't coming on any more than normal.
And if you change your typical driving pattern (ie. road trip in the hills/mountains) remember the block may not be right for the load / heat generated. Don't melt your engine.
