I finally got around to replacing the coolant in my M934. What should have taken a couple of hours at the most, ended up eating up the entire day. I knew something was wrong when I opened the drain cock and nothing come out, that is until I took a small Philips head screwdriver and poked it around in the drain. It was plugged solid and took 5 or 6 good jabs to get thru all the crap that had accumulated in the bottom of the radiator and get thing flowing, and flow it did as evidenced by the attached pictures. I make coffee that's lighter in color than the **** that's been circulating in the trucks cooling system.
After filling and draining the system 3 times without getting any results other than more of the brown stuff, I put in a couple of bottles of Prestone flush solution and a back flush tee. I let the truck run for an hour with the flush solution installed and then drained the system and started the back flush process. I back flushed the system with the truck running for over an hour before I finally got clean water coming out of the top and bottom of the system.
I also attempted to change out the shutterstat, but the unit I purchased was too long and the bulb ended up hitting the thermostat, so I've got to send it back and get one about 1/2" - 3/4" shorter. I put the old one back in, buttoned everything up and installed 6 gallons of Prestone and 3 gallons of purified water. I'm assuming that the remaining 3 gallons of water is what remained in the engine, but I'll find out if I need to top the system off with more water later today when I visit the beast.
With as dirty as the system was, the truck never ran hot, always showing +/-195 degrees on the temp gauge. I guess anything is possible when you've got 48 quarts of fluid circulating...