Step one: drain the system. There is a petcock on the right side which you use to drain the cooling system, only it's up in a tiny little crevice through which Jeep decided to run a bundle of wires, thus reducing the total available space for opening said petcock to enough for one thumb and finger. Of course I did not have enough room to apply enough torque to move the thing.
After a few minutes' fiddling I got the small channel lock pliers, and after more time wasted on fiddling I got the thing loose enough that I could start unscrewing it with my fingers. I could only move it so far with my right hand, so I had to switch to my left, and after several alternations I realize that I was tightening it when I switched to my left hand.
Once I got it loose and water started coming out, it got more fun, because quite-literally-ice-cold water was running up my sleeve while I groped blindly for the petcock. There is one path to the petcock, and I cannot look and reach in there at the same time, because that would be convenient.
But I got the thing draining, then went inside to wash coolant off my hands.
Mrs. Fungus: "Is it working?"
Me: [brief pause while I come up with a reply that won't make her kill me] "I haven't even started yet."
So I go to hook up the hose, and get the flush nipple plumbed in, and turn on the water, and...nothing. I said more bad words: the hose was frozen. I tried getting the hose from the back, but that was also frozen, and then I tried stretching the nylon stowable hose...and the miracle of the day happened: it reached the damned spigot.
Flushed a bunch of gunk out of the engine.
Put the plug back in, got the flush stuff into the radiator, filled it with water, started the engine, put in more water, put the rad cap on, let it run until hot, shut it off, went inside.
Waited a bit, then went to hardware store for CLR. I tried taking off the rad cap, and it was already cool, so I left it while I went to the store.
Got home, pulled petcock out to let the system drain, hooked the hose up to flush out the dirty water and flush chemical, and...no water. Hose was frozen. This was the nylon wind-up one, though, so I took it inside and put it in the bathtub and ran hot water on it until it was no longer frozen, then went outside, hooked it up, and flushed out the cooling system. I left the water running and kinked the hose to unscrew it from the fitting.
Got system configured to blow core out with compressed air. Forgot that even if I turn the regulator down to zero, the hose is still pressurized until the hissing stops, and blew rusty crap all over the place, including my face. Went inside, washed face and rinsed out mouth, then resumed work.
Finished blowing out heater core, filled it with CLR, then went to work on putting the radiator drain plug back in. That took a long time, not the least because I forgot to switch directions again, so when I was tightening with my right hand I was loosening with my left. MOTHERFU--
When that was done, I figured it had been long enough for the heater core and blew it out again, then flushed it with water, spraying myself with freezing water in the process. Flushed clean.
Put everything back together, refilled radiator until full. Started engine, filled radiator until full. Put cap on, shut off engine, took off upper heater hose, filled until coolant came out of hose nipple on thermostat housing. Buttoned everything up. Started truck and let it run until hot.
Heat: not present without running engine over about 1,800 RPM.
FFFFFFFUUUUU--
So I decided I'd take a trip to the gas station and fill the tank before it gets expensive next week. When I got to the gas station, the temp gauge was over 210 and the auxiliary cooling fan was running, but the air from the vents remained warm only for a little while at idle. When I checked it again while filling the tank, it was tepid again. Meanwhile aux fan was still running and temp gauge was still over 210.
On the way home, the air from the vents stayed nice and hot, but the temp gauge was still too high and the aux fan was still running. Ordinarily the temp gauge stays a bit under the middle line, but tonight it was that far over the line. The temp gauge went down a bit as I drove home, though it never went below the middle line.
Parked in the driveway, sitting still at idle, with the temp gauge that high, air from the vents cooled off.
At that point I decided it was probably the water pump failing, which did not help my mood one whit. Went inside, saw that Og was on-line, had a text chat with him, and he confirmed my suspicions. He was suspecting air in the system until I told him how I'd filled it, at which point he said, "Well, now it sounds like a water pump," and I said many bad words.
On the plus side, a water pump for a Jeep Cherokee is not an expensive part. I'm going to replace the thermostat at the same time, because they cost peanuts. The Jeep has a bit less than 118K on it, so it's not terribly surprising that it might need a water pump.
Even so: argh.