Ok, problems with my 1999 Jeep Grand Cherokee 4.7 ltre. I put in a used radiator,thermostat<( New)... heater core, and NO Heat :( HELP!?

Air in the line or clogged heated hose(s)/core.

Easy way is to let the car idle, turn heat and defrost on full, let run for 15 minutes. That should get any air trapped out.

If clogged, you'll need a cooling system flush.

If it doesn't circulate it does over heat. You didn't check the water pump.

It was a new thermostat, sorry about that,new heater core. I ran Prestone Super Flush through the whole system, i bled it until i got all antifreeze coming out (No Bubbles)

Thank You so much for your answer.....

A used thermostat?? A new one is as cheap as they come. As for the heater core, did you make sure it was not clogged. Have you properly bled the cooling system to make sure there is no air bubble preventing coolant flow through the core?