open system, new hose, overheat

91 XJ with 4.0

I had a leak so I replaced the heater hose that is connected to the thermostat housing. Now the jeep overheats. I can't make it across town without the idiot light coming on. As soon as the light comes on I blast the heater and it will go off. My first thought was that I had trapped air in the cooling system. But since I have an open system it should self burp and this should not be a problem right? I did park up hill and run the jeep with the heater on and without a radiator cap, filling the radiator as the level went down. Some air seemed to come out but it didn't help the problem. I read about burping by removing the temp sending unit, but that is only needed on closed systems right? So what do you think happened? Suggestions? Thank you.

I just changed my rad out bout 3 wks ago...I too have the open system.....Mine overheated but didn't make it to the red mark...So I went back to the house and put some more 50 50 mix anti freeze in (12 qt system)as of today haven't had any "overheat problems.....I put almost 12 qts in....got a little left over in the 3rd bottle....Gauge stays right at 195...So MAYBE air can get trapped ......Try and see if you can ghet some more in the system.....try after it gets to op temp....double check and make sure you don't have the heater hoses swapped wrong....BEEN THERE DONE THAT MADE ME LOOK LIKE A FOOL:yelclap:

Start the jeep and keep your hand on the radiator. Make sure the radiator starts to get warm/hot after the t-stat opens.

I have experienced issues where with so much air, there is not enough to properly pump water. It is obvious because the radiator does not warm up.

If this is the case, WITH THE ENGINE COOL/COLD, remove the upper radiator hose at the radiator, and pour water in it (to fill up the head/block). I have had to do this on a few occasions with 4.0L cooling systems.

Thanks for the replies. I am sure I didn't mix up the hoses because I only replaced one. That is a funny suggestion though. I also know that the radiator is getting warm when the thermostat opens. The upper radiator hose heats up and when I put my finger in the radiator it is definitely warm.

Try squeezing the top hose flat with both hands. It is the highest spot in the system. I've had pretty good luck using this technique on closed systems.
The last time I replaced the water pump (in the wifes open system), I had to fill into the top hose, to purge most of the air. My temp. went right up near the red, the first time I ran it long enough for the thermostat to open. I figured I had an air blockage of some sort.
When I replaced the radiator a few years back, I had no issues at all. I sure can't tell you what exactly is happening, but it seems to be a sometimes thing.
You have to make sure the hose from near the radiator cap is not leaking, the one going to the recovery bottle and the recovery bottle has fluid in it. Look in the filler hole, they sometimes have a stain and look like they have fluid in them from the outside, when they are actually empty.
Your radiator cap is a two way valve, it takes pressure (around 15 PSI) to push the coolant out and there is no (little) resistance when the cooling system, sucks coolant back into the system from the *recovery tank*, during a cool down cycle (engine off). If the hose has a hole or is disconnected or the recovery tank is empty, it sucks air back into the radiator.

Definitely burp the system.

Definitely check your fan clutch.

Well thanks for the comments. I re-burped it. I didn't think I got much or maybe even nothing out the second time but it seems to have done the trick. I took it for a long drive without problems. Problem solved. Thanks.