[Diesel_Dave]

If your grille block affects your final coolant temp, then you've blocked off too much grille. The grille block should make the engine warm up faster, but not affect the final temp.

Your thermostat should control the final coolant temp by regulating the flow rate to the radiator. If your grill block has affected the final coolant temp, that means the thermostat is full open and has lost the ability to prevent overheating.