I'm getting different answers from people I know. Does anyone know 100% for sure?

 

Yes. The openings on the ends of the core tubes are different.

One end has a large opening and the other has a smaller opening. I believe the small opening is the supposed to be the coolant enterence and the larger opening is the exit.

 

Yes, just like Zinner stated. That's why when we do the dual pass mod you have to flip the cores around.