By pass hose

The way I look at it is without a coolant bypass of some sort (bypass hose, no thermostat, heater core) you have the water pump trying to pump coolant into a dead end. Think of what's happening any time you try to pump something into a capped hose, big pressure build up. Racers eliminate it but they also eliminate the thermostat or use a restrictor in place of the thermostat. Either way coolant can circulate. I wouldn't hesitate to restrict it some but I don't think I'd completely block it off unless I took the thermostat out (or used a restrictor). Just my .02