2004 WJ, 4.0 liter, auto trans, 2WD, remote trans cooler, approx 165K miles.
So, wife called me today, saw "smoke" coming from under hood. She immediately pulled over and popped the hood, upper radiator hose had blown off the top of the radiator.
Now, I installed that radiator about a year ago,I know damn well that hose was on tightly. And, I had flushed the cooling system at that time, the coolant was new/fresh. So, today I put the hose back on, clamped it down tightly, filled the radiator with some water so I could get it home. I started the Jeep and had it running while I added more water to the radiator to burp out any trapped air in the system, I kept watching the temp gauge and before I knew it, was just below the red line on the temp gauge, at the 240 degree+ mark, and that was with radiator cap off, no pressure. I shut it down, let it cool, had it towed home.
When I looked in the radiator neck, all I saw was thick brown goop, looked like a baby had taken a sh*t in my radiator. Can't be trans fluid as I bypassed the trans cooler in the radiator, running remote trans cooler only. Is it possibly oil?
I looked at the oil expectin to see a milk shake but the oil looks fine. I started to pressure test the system when I got home, pumped up to 15lbs, lost 2 lbsin 10 minutes, pumped up again and maintained 15 lbs for 10 minutes, then it started raining to I disconnected the tested and closed the hood.
So, I don't have a shop manual...so....what should I do? Pressure test again, this time for longer? Should I throw a thermostat in it and see what happens? What could all the brown crap be from ? My coolant now looks brown, I'm not sure if it looks oily though. Diagnostic help please.

 

That brown goop may be a leak stop additive called Bars stop leak.

 

Residual stop-leak possibly, but I replaced the radiator a year ago.

 

It could be rust sediment from the bottom of the block being stirred up after the overheat. There's only 2 things that I think could have built up enough pressure to blow off that hose; steam or compression leakage. With either of those the cap should be screaming venting it first I would think unless you have a suddenly blown head gasket.

BTW, normal pressure should be 18 psi.

 

Over heating with the cap off is a blockage. Id flush and new stat.

 

^ what dave said, check compression leak. A pressure test sounds logical, it should hold pressure firmly. You already did that. Do it again to make sure. I would also check into a new T stat, they are inexpensive enough. The housing for that is aluminum I think , and if it's anything like my ZJ, they frequently crack or fail, usually when you go to change the T stat. Those are available, Dorman has a nice one at Advanced for about $12 as I recall. You want a good stat, without the weep hole, like the SuperStat fron Stant. Flush and fill.
If you suspect a head gasket leak, can examine the plugs, or take the fluid to be tested at a radiator shop, they do that all the time to test for hydrocarbons for a head gasket or cracked head.