For me, servicing the heater core has only been from "others mistakes", case in point- my brother put 2 eggs in the radiator to plug a leak, on top of red pepper. I asked him if he wanted a few slabs of bacon with that. I make heat exchangers for a hobby of mine, and the ideology is the same in all cases- Mass of coolant surface area to the environment dictates the efficiency. Which is to say the core looks just like a radiator, only smaller. Air blows through the fins into the ducts to be redistributed throughout the cabin. The "tubes" that spread the heat to the fins get a slimey mixture inside them over time. This slime attract cations (sodium, calcium etc) due the net charge of the surface. The cations are released by the galvanic reation of the dissimilar metals throughout your engine. This is why most recommend using an alkali solution, so as to attract the cations and make a salt which you would see as a sediment and flush out. A similar reference is arterosclerosis, if you wanted to see what it looked like. The same thing happens in homes with copper pipes. Aluminum cores are more suseptible to galvanic reations, which is why you use a sacrificial diode in the radiator cap, and use coolant rated for aluminum radiators.

 

Thanks again for the help. I did as suggested, and reverse flushed the core with a garden hose.
For anyone else wanting to do this...
5/8" ID heater hose will fit very nicely into a 1/2" PVC fitting. So you can use a garden hose to female adapter, then a 1/2" pvc male adapter to connect the garden hose to the heater hose.
Then attach the garden hose/heater hose to the heater core, then connect another length of heater hose to the other nipple on the heater core. This will act as a waste line.
Now you can slowly turn on the garden hose from the spigot and watch the nastiness flow out. Once it runs clear, turn off the spigot, then move the 1/2" male adapter/garden hose to the other hose and reverse the flow again. More nastiness will flow out. Do this a few time and you are done.

Now that coolant is flowing through the heater core I have a little bit of heat, but it doesn't get too warm. The coolant gauge on the dash only warms up to about 1/3 warm so maybe that is why the heater doesn't get hot????? I am just glad I have some heat now!!!!!!!!!!!!!

Zac

 

Just saw this, missed it last week. Before I rev flushed her heater I replaced tstat, hose itself and the hose to block fitting. The fitting that goes over the tstat. Reason for fitting replacement was on our 3.9 it was old and the projectons on the plate side were crushed flat. Learned a long time ago that could be a leaker on reinstall and the thing is cheap and you only do it once no leak. Anyhoo, engine temp started running much better. I then flushed heater core, but I flush reverse then fwd, three times to get clear water. Now the little succor will drive you out of the cab.