Originally Posted by Ace*Of*Spades
Right now I'm under suspicion that the heater core might be the problem. Airflow isn't an issue, and the radiator was recently replaced because the old one was cracked. Heater cores can go bad when the radiator does can't it?
One check for heater core being blocked to water flow is after the car is hot put the blower on high and on full heat let it run for a while then feel both radiator hoses.
Typically the one will be hot with water going in and the other will be cooler. The water flows through slowly and the heat is extracted from the water by the blower. The water coming out is way cooler. You can try running the motor at 2000 rpm and see if that makes a difference pushing water through faster.
I had one blocked some and I disconnected the hoses and poured the radiator flush chemicals into it and let them sit. Drained and let them sit again. It dissolved some of the gunk.