Yesterday I had some problems out of my cherokee. I took it on a highway trip with the family. We drove for about half an hour at 75 mph with the heater on full blast with no problems. Then we turned off the heater.... About 5 minutes later there is steam coming from under the hood.

The radiator overflow was going like a gyeser and the hose wasn't connected to the overflow bottle. Drenched everything. It was pouring right on the distributer cap. Well that fouled out and it started running rough and loosing power.

I ended up driving to the next exit (about 2 miles) where it stalled out at by a gas station.

I waited about an hour for it to cool off and went out and put 2 gallons of liquid in the radiator. I then drove it for about 10 minutes with the heater on... no problems. I poped the hood and everything seemed normal except the top radiator hose was obviously under extreme presure, it was rock hard it had so much presure in it. (it is a fairly new and very flexable hose) I decided that the system was probably building presure because the thermostat was stuck closed. I whiped out my sockets and went to pull out the thermostat. There was no thermostat someone before me aparently took it out.

So I put everything back together and drove it home with the heat on full blast. It seemed OK but the system was again building up lots of pressure. I am thinking it may be the water pump not letting anything by. Any help would be apreciated!!!!!

Although the 4.0L six is not known for blowing head gaskets, have the cooling system tested for the presence of carbon monoxide.

The thermostat should be there or it won't flow properly.

A blown head gasket was one of my thoughts. However it seems unlikely because there is no water in the oil, and I have full power now that the distributer is dried out....

I wasn't trying to take out the thermostat as a permanant solution, I just wanted to limp home. I figured that no thermostat was way better than one that was stuck.

Maybe it could be something else?????

Sounds to me like everything is working ok - at highway speed with heat on, so I'd think that the thermostat is ok.

My thought is radiator. After 8 years it could be getting some buildup on the inside; I've known of several vehicles that overheated with just a little cloggage in the radiator. How often do you change your coolant? When it overheated was it a bit warmer than it had been before?