Ok guys I have a weird issue with my 99 XJ sport, 4.0, auto. The temp gage rides at 225-230 which is understandable since I live in Las Vegas and its... BLOODY HOT!! But every once in a while the temp will jump up to 250 (one line before 260) my check gage light comes on. So I'll turn off the a/c and cruse for a maybe a min then it drops right back to where it normally rides. Also if I'm pulling a hill or trying to pass someone on the freeway it does the same thing.
If I'm just driving in normal traffic and not running the a/c it won't do it. I've flushed the radiator, replaced the thermostat, changed the temp sensor at the thermostat housing, Checked both elec fan and clutch fan all good...
This is driving me absolutely nuts!! Please someone tell me you know what this is about... Keep in mind I'm not losing any coolant when this happens either.

Once again thank you for any help, info

 

I just went through a similar situation, but my radiator completely threw up. Im sure soembody else knows better than me, but Once I put in a new radiator, it still overheated. And what eventually did the trick for me was a new water pump, even though mine didnt show any signs of being bad. But sure enough that fixed my problem, another thing you could try is changing out your thermostat, not sure if that fits your problem, but it is a cheap part and easy to change. Maybe look into it, but good luck!

Edit: just saw you changed thermostat. Maybe try water pump

 

That might be my next step, was hoping that wasn't the issue but it may end up being that... If not I'll have a new water pump at least lol