Mini Cooper coolant issue
 

Working on a 04 mini that was bubbling coolant out of the overflow. We changed the thermostat and went to fill the system. Opened both bleeders and got coolant out of the lower bleeder but little no no coolant going to the top bleeder. And it seems to be taking it real slow when pouring it in. Clogged system and if so is there a likely place to start the search?

Thanks john