New Water pump now overheated
87 YJ, 4.2 radiator and heater core were leaking, so last week I put in a new heater core and had the radiator fixed. Installed a new thermostat and filled everything back up. Drove to work the next day and my water pump blew. I replaced the water pump with a new unit from Napa, not re-manufactured. Let everything set up for a day. Filled up the radiator yesterday and started it up. Usually the pump starts circulating immediately and you see the fluid in the radiator drop, but nothing like that happened. I let it run for about 20 minutes and the only thing that happened was the engine temp started to climb. The radiator didn't get hot and the top hose was still cool. It was like I wasn't getting any circulation at all. Do I need to fill up the engine block with fluid in order to prime the new pump or something? I have never had this problem before. Thanks for the help!