1990 Jeep Wagoneer HELP! '90 Wagoneer overheating >.&

Engine Cooling problem
1990 Jeep Wagoneer 6 cyl Four Wheel Drive Automatic 210k miles

Allow me to start by saying thank you for all the folks who are going to assist me with this huge problem of mine. Your time and advice is very much appreciated, as I have exhausted all my resourses thus far. That being said.

About a week ago, my wagoneer started to billow steam out of the hood while I was at a red light. I pulled into a parking lot and opened up the hood, only to find that my overflow tank had cracked for the third time this month, and was spraying water out of the newly formed crack in the side of it. I was luckily able to get it down the road and into my driveway, which is where it has been sitting for the past week now.

To my knowledge, I have tried everything there is to do to get this bad boy running again. I replaced the overflow tank, but noticed that after doing so, steam was coming thru the hoses and into the tank. I am going to assume this is what made the tank crack so many times.

Following the replacement of the overflow tank, I took out my radiator and cleaned it out real good. I didn't use any professional cleaner on it, just ran a bunch of water from my waterhose thru it. It came out brown for a minute, then changed to the clean/clear color that water should be, so I'm guessing I did that right. I then detached as many hoses as I could, and ran clean water thru those as well, thinking that maybe I had something in one of them, causing the coolant flow to be restricted.

The coolant is flowing thru to reach the overflow tank, and I can't see anything leaking out of the weep hole, nor can I hear any odd sounds coming from the water pump, so my best guess is that the pump itself is working fine. Taking out the thermostat, I found that it was stuck in the open position, so I went ahead and replaced that as well.

Okay, so here is the problem I'm running into now. After doing all of this work, I replaced the system with fresh coolant and a bit of clean water. I started my disconnecting the hose that runs straight into the radiator, and filling that up first to minimize the amount of air in the system. After that, I dumped the rest of the coolant/water mix straight into the overflow tank. I left the tanks cap off, and started the jeep up, but after only a few minutes of idling, It started to boil the coolant and blow steam from the overflow tank. I recently put clear hose to and from the overflow tank, so I could see what was happening with the coolant, and noticed that there is a bunch of air flowing into it from the system still.

After I realized that the coolant was boiling, I shut the car off, and it only seemed to make things worse. I saw that not only was air coming INTO the system, but it was also leaving OUT of the overflow tank, and going straight back INTO the system. This only happens when I turn the Jeep off. Though. As long as its running, only coolant will flow back into the system.

Also, I noticed that my electric fan will not cut on no matter how hot it gets. The jeep will be overheating, steam pouring out, adn yet the fan won't so much as budge. I hooked up wires from my car battery to the fan plug-in, and it works just fine that way, so I think I may just make a toggle switch on the instrument panel, rather than try to figure out what is happening with that. Just wanted to give you all the facts though, you may find them more important than I did. NOTE: I have tried running the ran while filling the coolant, but the same problems happen. The jeep still overheats, the coolant still boils out, and it doesn't even take it longer to happen. Its like the fan has no affect at all - no matter if it's on or off.

So here I am, completely lost and confused. I have had everyone that knows anything about cars come take a look at it, and they are all just as confused as I am, so I decided I would try this site, hoping that maybe someone else has run into this same problem. I would greatly appreciate and help or advice any of you can give, trust me-I am out of all other options. I hate to take my jeep to a mechanic when I am positive that I can fix it myself, so please, help me bring her back to life!

Thanks in advance for all your help,
Zach

By the way, if you need any more information, or pictures of anything, please let me know, I can easily provide both at a moments notice. Thanks!