The last piece of the puzzle arrived at my doorstep last evening, a replacement thermostat housing to replace my bent one.
I must have bent my old one while over tightening it 3 weeks ago on my Seattle trip, when the cooling system first started acting up. Guys that work on their own vehicles know the drill, 11pm at a truck stop on my way to Seattle, thermostat stuck closed, oil pan hot, radiator cold. I had my all my niece's worldly belonging in my trailer, and it's raining, I've got 1000 miles more to go, 3 days to get it done. I removed the thermostat and replaced the housing using RTV. It leaked. Cold, wet, tired and in the state of denial, I tightened it more. It still leaked. Don't try this by the way, run without a thermostat on a 7.3 Diesel. The housing to front cover connection relies on the thermostat's channel o-ring to keep the coolant from escaping. I wound up cutting the innards out of the thermostat, reinstalling it with just the outer ring part and channel o-ring, to seal it. Things are so much clearer while turning wrenches at home, in daylight, near all your tools and creature comforts nearby. Awe, the things you learn while trying a roadside fix. Nothing good happens at a truck stop after 11pm
Last night, I did one more soapy water flush, a clear water flush, new thermostat and housing, new overflow/gas bottle cap, took it for a 10mile test drive.
The lower hose popped off while on the road. Turns out, just like my coveralls, the inside of the hose is still slippery from the residual oil. At the smallest pressure increase the hose popped off the lower radiator nipple. My pressure was kept at bay knowing my GF was cooking up a nice meal, and had a glass of sparkling waiting. Simple fix, I cleaned the inside of the hose with brake kleen, scrubbed it with a wire brush, and added a second hose clamp for good measure.
Added 50/50 coolant mix and went on a second 10mile test drive, coolant temp coming up as expected, engine running smoother as a result, no longer in 'cold start mod' I suspect, the system is holding pressure