Decent Garage has a video on cleaning out your heater box. I am rather dubious on the fancy plumbing.

 

Heat should work great stock, if not figure out the problem.

 

After watching one of cutterup robs videos on the fleece bypass system (titled "HOW TO WASTE $500 ON A COOLANT BYPASS ON YOUR CUMMINS") I think I have a more thorough understanding of the coolant flow route. I didn't realize how small the coolant orifices are on a GOOD gasket, my headgasket had all of the block to head passages from cylinder 1-5 completely blown out and wide open. I didn't take the time to look at the new gasket to realize that they're only supposed to be tiny steam holes.

I guess that resolves my heater issue



Is there any risk of blowing the freeze plugs behind the tappet cover if everything else is sealed off with solid billet plugs while spinning 4K, Is a pressure bypass even necessary?

 

The frost plugs are secondary IMHO. Without a bypass - at high rpm - you are creating a hot spot at the back of the engine. (Poor cooling of #6.)

 

Okay, I'm playing the devils advocate here, I've heard of this "hot spot" a few times now and I wont disagree that they would logically be hotter than 1-4, but I also don't think there's an issue with with the temperature difference. I've hit mine with a temp gun and it only had a 14* F variance front to back.

On top of that, the coolant temp sending unit is directly above the only wide open coolant passage from the block to the head, and that happens to be smack dab in the hot zone of cylinder 6. So if it truly were getting hot as you made runs, climbed grades etc, you'd 100% see it on the gauge. The first thing to flow past the sender is the hot water back behind cylinder 6.

I can understand the logic of wanting cylinder 1-6 to be 100% equal in all variables, but I'm not sure that temp alone is enough reason to add an external coolant route.

 

I’ve done similar towing,turbo and fueling mods to my 97, 03 and now my 12 and I ran the crap out of all of them when towing in the mountains, and I never had any head gasket, burnt pistons, or any particular hotspot problems.
With all the hoopla over pressure and temperature differences, I finally put thermocouples and test gauges on my 12 and there was no difference in temperature or pressure between the front and the back of the engine.
BUT, I know some of the early 5.9s, particularly friends with 94s, had some serious heating problems.
With all the changes they’ve made with the castings and coolant circuitry, I think you will need to do your own experimenting with pressure and temperature, to know for sure.
I remember my 97 had two steel tubes running down the passenger side of the engine to the heater core but that heater would still run me out, in the winters.
My 12 gets the heater HWS from the back of the engine through a 3/8” nipple in the head, and I didn’t want that heater water bypassing the radiator, but I didn’t want to shut it off completely either.
So I put a three-way ball valve at the top of that HWS nipple so, in the summer, I can direct that heater flow to the top of the thermostat housing, so it also goes through the radiator.
This might answer your question about how much bypass flow it takes to affect the cooling… if it is anything but summer temperature, I have to keep that water flowing through the heater core, and not bypassing the thermostat, or the engine won’t warm up.