Heater Core install basics. To install, you remove the heater core housing in the engine compartment. There are two bolts between the case and the passenger exhaust manifold on the firewall. The other two nuts are inside the cab on the passenger firewall, up behind the a/c assembly. Total of 4 nuts to remove to get it out. Then, there are about 16 or so small screws that hold the heater core housing halves together. Take them apart, clean out the core housing (usually filled with pinestraw and leaves), remove the old core, pop in the new, put it back together (I use RTV between them, as well as weatherstrip from home depot around the vent door) and then reinstall. Super easy.
I also like to quickly sand / scuff it and apply several coats of exterior grade metal primer and several coats of exterior grade metal paint while I'm at it.
I also like to quickly sand / scuff it and apply several coats of exterior grade metal primer and several coats of exterior grade metal paint while I'm at it.