So a couple weekends ago the TJ 4L started overheating while going 75mph, ~85 outside, with the A/C on. It got up to 240 at one point, so I stopped, opened the hood, let it air out, and went on my way without A/C. It got up to 230 again, so I stopped and got some belt dressing cus my handy phone has internet. I think that helped. It did it on my drive home going less than 60 later that week, again I think the belt dressing helped. There was some oil on the pulleys, I took off the belt, spun the pulleys and cleaned them a little, the only one with drag was the power steering but I assume that's normal. Autozone guy said my belt might be too tight. My coolant reservoir went down some from full but not empty so I assume it has enough.

Only happens when it's in the 80's, the A/C makes a difference, nothing is making noise, I'm kind of at a loss. I'm relying on my aftermarket thermometer, maybe I should hook up my laptop while I drive?

I can't, for the life of me, imagine how belt dressing would help keep things cool. That stuff is to keep the belt quiet.

I remember a post a while back about someone overheating at highway speed. They ended up putting on a new cat because the original was clogged.

Also, you can run the heater full blast (assuming your heater core is not plugged up) to help cool the engine while driving. At least you won't have to stop driving. Unless it stays high.

Ah, the belt dressing was in case the belt was slipping and not making noise, maybe more of a placebo. I will try to find that cat post.

My bad, it's on another forum. It's titled "temperature creep at 55mph plus. Help!"

Google that and you should find it.

I took it to a mechanic and he ran a system pressure test and a head gasket test (for free, nice guy), and he basically told me to replace my radiator because everything else was fine. He called it a 'capacity' issue, that my radiator must have some blockage. I replaced it with the Mopar original and now it barely goes over 200F in the exact same conditions as before. Problem appears to have been solved for a couple hundred $$ and I got to tinker a little.