Heater core

Follow your heater hoses. Will have to be a inlet and a outlet.

 

look under your passenger seat

 

It's easy to replace. As said, it's under the passenger seat.

 

if it is the same as other ihc's--you will have to unbolt the panel that holds the seat down--and seat belt i believe--then the whole works lift off and it is underneath--its not bad to do--just different--and a filter under the access panel on the right of pedastel
just to make sure--like tarps said follow the hoses---no need to drain rad--just pinch off the hoses

 

As mentioned under seat. I drove an international that never would put out heat except when you were driving at high rpms and even then it wouldn't always work. They replaced the water pump, heater core, lines, filters, checked for cracked head or blown head gasket, etc, etc, and a couple more etc's. Neither they nor I ever did figure what the caused it but somehow it would get an air bubble in there or something along that line and therefore couldn't transfer the heat. Made a long day even longer. Nothing worse then tarping a load down or putting on chains in the dead of winter then getting inside an ice cold truck not knowing if you would have any heat or not.