Alright, I have an 89 Jeep Cherokee that has a badly neglected cooling system. I think they ran straight water for the last 50,000 miles. The heater hoses have been replaced with AC refrigerant lines(!) The thermostat was nearly crudded shut. I got the Jeep cheap because it had a bad rear freeze plug. After I pulled that plug, I pulled out about 8 ounces of crud from the block.
I know this all can't be good. I'm replacing what I can. The radiator will get replaced as soon as I can afford it, since I want a nicer piece.
What I really want to know is what can I do to get rid of the crustiness in the engine. Is an off-the-shelf chem flush enough? Should I go more drastic? Vinegar? CLR? I want that motor as clean as possible, and I really don't care if it kills anything else as a casualty of war. It's to be expected at this point.
I've used those in-line water hose hookups before, but they've always leaked. Since I'm replacing all of the coolant hoses, I can cut one up and not worry about it.
So what say ye, wise men of the motor?
Saw more than one of those in my daze at the Jeep place. Fixing it is nasty and tedious but not rocket surgery.
Okay, first thing: don't do this on concrete! Rust stains are hell to remove.
If one freeze plug is rotten then the rest aren't far behind. I recommend pulling all of them you can (and there are two behind the flywheel!), then take the water pump off and flush the block with clear water while the FPs are out. Do this at least a few times, then knock in some new plugs. Then it's time to replace (not reinstall) the water pump. There are cheapo pumps out there which have cheap stamped steel impellers that literally rot away. See if you can find one with a cast aluminum impeller. Check the thermostat housing, they are known to rot from the inside and are cheap.
I'd also reverse flush the heater core and the radiator with clear water, again several times. The radiator reverse flush works best if removed from the car and turned upside down, you stick a garden hose in the nipple that goes to the water pump and turn it on full blast. All kinds of crap will come out of the radiator. Obviously the heater core is a bit more difficult to do this with. 
On that, just clamp a piece of heater hose to the outlet side of the core (that's the side that goes to the water pump nipple) and stick your garden hose in there, then turn it on; water will now flow out of the inlet hose which is the one coming off of the thermostat housing. I saw one disgorge what looked like a dog turd, it turned out to be Stop Leak. The heater worked a helluva lot better after that.
Reassemble everything, then flush with a chemical flush. Do this twice and leave the thermostat out whiile doing so (more coolant/chemical flow). Follow with a last rinse of clear water, then install a thermostat, fill with antifreeze mix and anti rust.
Check again in about 6 months, don't be surprised if the coolant's nasty again due to crap flaking off the inside of the block and working loose from various corners. Flush again with chemical flush and clear water and you should then be good to go for a while.
Be aware it's a PITA to burp air out of one of those things, quickest/easiest way to do it is to take the highest heater hose off while filling and wait for the coolant to run out of the nipple on the thermostat housing. Otherwise the engine temp will shoot to the moon until the thermostat finally decides to open.
I went through exactly the same thing a few months ago with an 83,000 mile 98 Jeep.
I bought it with a holed radiator and knowing that it had been overheated. It had a leaking freeze plug, and I decided to pull the water pump, hoses and thermostat at the same time. I made an effort to salvage the engine, but in the end I replaced it with a good used one.
I had flushed the old engine and and the heater core in both directions until everything came out clear, but when we tore it down later, we were shocked at how much remaining sludge we were able to scrape out of it.
Ok, so at least I'm pretty much on the right track. I have flushed as much crap out of the block that's coming loose with water. Water pump is brand new, and still looks brand new. The PO got rid of it because he wasn't gonna drop the transmission. The rest of the freeze plugs have been replaced, except the one in the back of the head, which i can't really get at to drive back in.
Isn't the second metal plug at the back of the block a cam plug? What I mean, is shouldn't it be bathed in oil and not coolant? That plug still looks brand new from the outside.
Woody, my motor isn't as crusty as yours was. Given the other things hacked on this Jeep, it was just a matter of time, though.
The head's freeze plug will get replaced when I swap heads. I want to get rid of this Renix head and get something that flows a bit better.
I still want to strangle the idiots for putting a remanned motor in this Jeep and not changing out the freeze plugs while it was out. It runs fine, but it looks like a DuPont reman to me.
EDIT: And I'll give a cookie to whoever can tell me what the PO used for the water pump and thermostat gasket.
Bud Lite box?
(Somewhere, there is a photo of a 12A with "Miller" sticking up underneath the carb)
Nope, I would have expected that.
They used the box from a computer motherboard covered in blue RTV. I'm gonna pony up for some $1 gaskets, LOL.
So is the coolant all rusty-brown? I've tried flushing the system several times and after 5 minutes of running it gets nasty again! I'm pretty sure this nastiness is making the coolant boil over a lot faster...
You may want to do some flushing with a hose when you do the freeze plugs. With each freeze plug I removed, I found a thicker pile of sludge behind it, as I went from front to back.
Like I said, the rest of the plugs had already been done. The PO just didn't want to get to the one that was actually bad. He wasn't the best at diagnostics.
When I got the Jeep, it was bone dry. I've flushed and flushed with clear water and it's coming out clear, but I still SEE the rust inside.
