99 Xj cooling system problem

Recently I suffered from a small leak in my radiator. I replaced it that same day with a new oem rad. After filling both the radiator and reserve tank with coolant I drove it a short distance to let the system take the coolant. Since it hadnt taken all the coolant the system needs and was running over normal operating temperature I then brought it home. I expected to see the reserve tank drained but it was at the same level as before. The pipes all had good pressure and no coolant was leaking nor was any hissing noise. I have continued to fill the radiator with as much coolant as it will hold thus it runs at proper temperature now. But why isnt it functioning properly? It just uses whats already in the system and does not take anymore from the reserve. I have a new thermostat and I doubt its the water pump since the engine is running at proper temp now that I have topped off the rad 500 times.
Its a 99 Xj with the 4.0

The open cooling system overflow tank holds any excess coolant when the system is hot, and allows the system to expel any air bubbles. The system will not draw any coolant from the tank until it cools down. If the overflow tank hose is clogged, there will be no flow either direction.