I have another question concerning the heater core. At one point some months back I thought mine was leaking. After locating and repairing some other coolant related issues the core itself is no longer a problem.
There are however, some issues with the doors/passages that direct airflow through and around the core and out the vents. Not that big of a deal, and I can live with that. While experimenting/determining the condition of the core I blocked the heater hoses from flowing coolant through it at various times, and was told that I can't do that. That stopping the circulation of coolant through the heater hoses will cause problems with the cooling system (4.3 engine) and the hoses must be connected so flow through the ports on the engine is uninterrupted. I've never had that theory presented to me concerning any car or truck I've owned.

Is there anything to that or is it just a crock?

 

You can unhook the hoses at the firewall and hook them together with a simple hose fitting if you need to bypass the core. I don't have an answer to the flow question but the work around will keep circulation normal

 

Yes, I'm aware of that, and did at one point. I also ran for a week or so with both hoses plugged. I recall no adverse reaction to that. The engine seemed fine, the temp gauge acted as always, and I saw no indication that any sort of problem existed. It's just that the shop working on the engine told me I couldn't run it that way or it would cause some sort of overheating problem. I didn't (and still don't) understand why. Simply closing off a heater circuit has never been a problem with any vehicle I can remember. What's so different about this one?