Thus refreshed, I set out to accomplish the task du jour.
Moved the bikes and other stuff around in the garage to make room, then pulled the Jeep's nose in. I had plenty of light and plenty of room to work. Next step was to consult the manual to make sure I was approaching the problem correctly; but for a couple of minor details the plan I'd made was fine.
Disassembly was a learning process, as always. It's been about a decade since I last changed the water pump in any vehicle, and I'd never done it on a Jeep I6 before, so I had to learn which wrenches to use--this 1/2", or that one?--but it was not difficult and to my surprise none of the bolts really gave me any serious trouble.
That made me afraid.
Had to drain the coolant, because otherwise I was going to make a huge mess. With the fan removed, I was able to stick the cage lamp next to where the petcock was, and I was able to unscrew it rather quickly. I let the coolant trickle out into the coolant drain pan (the special one I use only for coolant, because sometimes you can reuse it) while I completed disassembly.
Took the thermostat housing off first, once enough coolant had drained that it wasn't going to spooge everywhere. The gasket was a FelPro gasket--and it's only been on a year!--so it came off handily. That gave me room to get at the water pump.
The bolts holding the pulley to pump had given me some trouble, but I used one of Og's tire spoons as a prybar to hold the pump steady while I loosened them. (Protip, for future reference: loosen these first, before loosening the fan nuts.)
Had to finagle around with wrenches some more to figure out which ones were most effective at removing the water pump bolts, but shortly I popped it off the engine, and had a gander at it.
Okay: the impeller was not at all rusty, and it was very firmly mounted to the shaft. I said some bad words, but then noticed that when I spun the thing, the bearings made a lot more noise than I am comfortable hearing from something that routinely spins in excess of 3,000 RPM. Even though the impeller was not the source of my problem, the bearings are bad (or going bad) and the pump actually needed replacing--just not for the issue I thought.
Took the heater return line off the old pump, cleaned up the threads, put on teflon tape, screwed it into the new pump, more or less to where it needed to be. I also cleaned up the water pump bolts while I had the bench grinder running. I took a personal interest in cleaning the old water pump gasket off the engine block, and once that was done I was ready to start reassembly.
Got out the "airplane sealant"--I looked at that bottle several times and resolved to remember the correct name, but have already forgotten what it is--and applied goo to gasket, then applied gasket to pump; put more goo on the other side, and then finagled the new pump into position. Got the bolts in, remembering to put some thread sealant on the one that wasn't in a blind hole, and got everything torqued down. It took me longer to find the right wrench than it did for me to tweak the heater return pipe into the right orientation.
Hooked up lower radiator hose, tightened clamp, then turned my attention to the thermostat housing. I made sure the mating surfaces were clean, then put the new thermostat in and treated the new gasket with the airplane goo. Cleaned off its bolts with the bench grinder, then got the housing back on and torqued down.
Looked around, trying to figure out what I had forgotten, then realized that I had forgotten nothing, and that it was time to put the radiator drain plug back in.
I put a bit of oil on it, smooshed it around, then wiped almost all of it off, but I was able to screw the thing in one-handed without having to move at all. In retrospect I probably should have used silicone spray, but since I wiped nearly all the oil off the thing I doubt it's an issue. I just needed a little lubrication to make it easier to turn, and it surprised me by going in so easily I was dismayed that I didn't think of this expedient the other day. "Wait--that's it? It's in all the way?"
Got back up, then decided to put the front end of the engine together before refilling, but I wanted to make sure that damned plug was in before I forgot it and dumped fresh coolant all over the garage floor. Water pump pulley went on without a hassle; the fan was a little more difficult, but not much, since the fan shroud is long gone. Hardest part of this phase was figuring out how the serpentine belt was supposed to be routed; it turns out that there's no label in the engine compartment and the one in the Haynes manual is for a different variant. Once the belt was on and tensioned, I torqued down the fan and water pump pulley bolts. Done and done, and now it's time for coolant.
Started filling by dumping it right into the upper radiator hose, and ran out of fresh coolant before I ran out of room. I checked the old stuff with the hygrometer and it said "-10", and when I checked the fresh stuff it said "-45"--so, f it, I needed more anti-seize compound anyway; I pushed the Jeep out of the garage and closed it, then went to O'Reilly's for anti-freeze and anti-seize.
Got home, pushed Jeep back in, resumed filling. Got the radiator filled up, then turned my attention to the heater core; once I was sure everything was full I buttoned everything up and started the truck.
Let it idle for a while while I put away tools and cleaned up my work area. After it had gotten all the way warmed up, the temp gauge was right where it normally is, and the heat was blowing full hot.
Mind you, it was about 50° outside, so "full hot" is not that hard to manage; every time I've worked on this thing's cooling system it's blown nice and hot when it's merely chilly outside. The acid test will come on Tuesday, when it's supposed to get back down to freezing, and I won't know one way or another until then.
Still, the air stayed that warm and didn't cool off, and the temp gauge was right where it needed to be, and when I opened the tailgate to put the Haynes manual back into my box of truck gear (tow strap, tire repair kit, other things) I was met with a faceful of hot air.
I really, really hope this is fixed now. Over the past five years I have replaced every component of the Jeep's cooling system except for the heater hoses and the heater core. I don't want to replace the heater core if I can avoid it (because "step one: remove dashboard") but if that's what it takes to get reliable heat out of this thing, I'll do it.
2012: Upper and lower hoses, thermostat, overflow hose
2013: Thermostat gasket, flush system
2014: flush system, replace thermostat and pump
The coolant jacket in the engine block is pristine, at least as far as I could see. There was no real rust or corrosion present.
The coolant jacket in the head, however, is rusty as hell, at least as far as I can see. With both thermostat and pump off, the contrast is striking, and now I'm wishing I'd thought to take a picture of it. That is just weird.
...but it looks to me as if the water pump forces water into the block, and it flows upward through the cylinder head on its way back to the pump. That makes sense: hot water rises and the engine block needs less cooling than the cylinder head does.
There is also the remaining fact that Jeep had some trouble with cylinder heads cracking. I do have plenty of evidence suggesting that coolant is seeping into at least one combustion chamber, but since the remedy for that is getting a remanufactured cylinder head and installing it, it's going to take some time for me to do that frickin' job. (Cylinder head is like a $600 part, for cripes sake. It's about $400 on eBay for a bare head, with no valves or anything. Yeesh.) I'm not afraid of doing that kind of work, but I really don't want to do it in winter. That is a summer job.
"Boneyard, bonehead!" You say. And yeah, I could go that route, but who's to say that I wouldn't end up with the same problem, or worse? A boneyard part would be cheaper, but I'd still have to get a machinist to check it for cracks, because I'm not going to install a used head without making sure that it will actually fix my problem. Besides, if I put a new head on the thing, it's going to have a valve job, because there is absolutely no sense whatsoever in not doing a valve job if you're replacing your cylinder head anyway. (Unless it's already remanufactured or brand new, blah blah blah etc.)
(Og used to replace the cylinder head gasket in his Escort without doing a valve job. That's different, because for him the head gasket was a wear part and he did it several times.)
Long story short: pump was failing, but not in the way I thought it was. Doing all the work I did today seems to have fixed the overheating problem and hopefully will also take care of the underheating problem in the cabin, but I won't know that for a few days at least.
It sure is nice being able to fix things.