Dear Dad,it would appear that if a portion of the cooling system was blocked off, the temperature would rise more rapid and perhaps obtain a higher degree! The only item that blocks off a portion of the cooling system is the thermostat. It's not a block off it's a valve. Most of us consider a thermostat as that which heats the coolant, True but consider while the coolant is being heated in the engine the remaining coolant is being cooled in the radiator. So it depends upon the season as to what the valve does. At the temperature rating of the valve(thermostat) it opens and musical chairs occurs and we change places. So you see as others have remarked, "blocking off" doesn't jiv. Happy Trails Beep Beep from 195 degree thermostat Houston.
a blocked off block head