2000 f150 4.6 4x4 heater core replaced 6 months ago, leaking again. any easy answers?

 

No easy answers. Could of had a defect who knows, but it still has to come back out.

 

Several - some of them are published in Ford TSBs regarding galvanism (incorrectly referred to as "electrolysis") and excessive pressure when cold. This site requires a e-mail to access, but it doesn't have to be your real e-mail:
http://www.bbbind.com/free_tsb.html

But until you tell us where it's leaking, it will be hard for us to help you. Got pics? What did you replace it with: a Ford/MotorCraft heater core, or the cheapest thing the zone sells? It matters. What coolant did you put in? That matters, too.

 

6 months ago tells me that the installer is faulty