Sounds like you got a placebo effect when you replaced the t-stat. Does the fan come one when the engine in idling? If it does, at what point is the needle on the gauge before it goes up? (when you're checking this out make sure the ac is off). Did you replace the coolant when you replaced the t-stat? You didn't put 100% coolant in it did you?

 

I'm only getting 168 degree max temp on thermostat neck. Fan does not come on when engine first started, comes on a little while later (147), needle on gauge not to half way yet. needle hits a tick past halfway and fan switches to high speed. What do you mean by 100% coolant, type or level in radiator. I added antifreeze back until it was to radiator neck, I did use premixed 50/50 coolant that stated it was good for all cars and coolant colors. Added less than a quart.

 

A few things:

The generic coolant you used may be part of the problem. Some non-OEM coolants mixed in can turn to gel.

Check coolant level (cold), top it up in the radiator, add some to the overflow bottle to at least the minimum level.

Seeing 168° max on the thermostat housing makes me think you are not pointing the infrared gun (if that's what you are using) on the right spot. Point it at the metal housing, just below the neck the hose connects to. When I do that on mine, the reading follows the factory sensor, as displayed on the AeroForce gauge, "almost exactly".
It's important to know if your engine is actually overheating, or not, before you spend any more time troubleshooting.

 

That was the right spot, it read 129 on plastic and 168ish on metal. This was just starting it in parking lot at work and letting it run until fan kicked to high speed and needle passed halfway on gauge. It was in the sixties outside temp. I trying to locate a temp sensor today to find out cost( may just put one in anyway).

 

Dealer only part, no one has one, will be here on Wednesday. Getting more indications it the sensor. When I started it this morning the gauge was already at mid point (outside temp 50's) Next time gauge pegged low and throttle control trouble light on, and fan in fast speed instantly. Turned off and back on gauge went to midpoint and fan did not run and trouble light went away. Guess I'm waiting on Wednesday for the part now.

 

168 is pretty low, infact, it's very low. Operating range should be between 190 and 210 (that's the general temp range t-stats open on new vehicles, haven't really checked on when the Jeep's open up).

Let me get this straight, when you start your rig for the very first time in the morning the gauge already shows a reading?

To follow up what ronjex said, make sure that you used a compatible coolant with the factory. If not, you'll end up with some nasty mess in your cooling system.

 

last couple of days, since overheat started back, gauge shows almost have way at start up. Two different temp instruments show same temp on thermostat housing. Max out at 168.

 

before you replace the temp sensor make sure that you have no frayed wires that are grounding out, bad connection/connector at temp sensor.

 

kinda thinking the same irratic readings, eng temp not up to spec

 

$5 part fixed it. Replaced temp sensor and all is good. Thanks for all the help figuring out this thing.....