If there is an air pocket causing cavatation. There would be no heat, due to the core being after thermostat and so high on the cooling system. Have you taken off the t-stat housing and fill at rad till you see coolant at the t-stst location? This should allow hot coolant to open stat allowing you to fully "burp" the system.

As I said before. pull the guage sender at the thermostat housing to bleed the air. If you pull the housing itself, you may get coolant on the gasket surface causing a leak, and then having to pull it AGAIN to reseal it.

I also believe the heater core is BEFORE the thermostat, allowing the heater core to flow before the stat opens. You may as well replace the temp sensor while you have it out with a new one. This will ensure the guage is reading right.

Older cars had a thermostat bypass hose to allow some circulation before the stat opened, this allowed the engine to warm slowly and not cause hot spots. Today, they use the heater core for this purpose. This is what's called a "full flow heater".

Check your radiator cap to make sure it's holding pressure. Without pressure, coolant will boil at 212*. With pressure, it will boil at about 250*.

I ran the engine to operating temp this morning. The upper hose on the t-stat housing was cold, until the engine temp gauge got to around 195-200 F and then the hose started getting warm. Does this mean the t-stat is working?

I let the jeep continue to run and the temp gauge gradually started to rise until it got close the max so I shut it off.

I don't think their is air inside causing cavitation but I will remove the sensor and try to bleed the air out like suggested.

Would air cause the overheating?

Everything was working before I drained the coolant (pulled the bottom radiator hose) and then replaced the t-stat and filled it back up.

Also, I'm almost positive the t-stat is facing the correct way, but is their a specific orientation it should be in?

There is a little hole on the t-stat, I think I put it towards the top. Would this matter for the t-stat to function correctly. I figured since the system was pressurized it wouldn't make a difference.

It's entirely possible the water pump impeller is broken. This is common on the 4.0. If it is, replace it with a PREMIUM pump with a metal impeller. On the 4.0, the impeller spins about 1/16" from the #1 cylinder barrel and any looseness in the bearing can cause it to strike the barrel and shatter.

The small hole in the thermostat is to bleed air out of the engine. It needs to face up but really isn't much good anyway.

Are both the upper and lower rad hoses gettijg warm?? Sounds like your engine isn't getting coolant. Take the thermostat out and run it like that see if it overheats. You could have a bad thermostat even though it's new. Seen it plenty of times.

Put the thermostat in boiling water and see if it opens up...

thanks....I checked the new tstat, it's good. I believe everything is working corrrectly, not sure about the impeller though.

The radiator fan is not coming on. Maybe the fan motor or relay?

I pulled the right headlight and cut open the bezel to reveal the relay.

It's 60 bucks though.

Should the fan come on once the engine reaches 195 F ? What about with the A/c running?

I was going to try giving the fan 12v and see if it's the relay..is there another was to test the relay?

OK i checked the tstat it's good. I replaced the cooling fan relay and now I have a check engine light coming on that says their is an open or shorted condition in the radiator fan relay circuit.

Could this be a bad fan motor?

I would shoot power directly to the fan just to make sure that it actually works. I need to hunt down why mine isn't working also. Lol

It should come on at a predetermined value (which I don't know in your case) and it should come on in intervals whenever you have the ac on

OK so I ran the code for the check engine light....

After I put a new fan relay in the check engine light came on.

Code says the ECM has detected an open or shorted condition in the radiator fan relay circuit.

So since the relay is new, it must be in the fan motor right?

I've read that the fan motor going bad will cause higher power draws and burn out relays.

What do ya'll think.

How should I jump power to the fan?