Well, I'm back with probs with my JAG. It's overheating on me in traffic. Stop and Go. I read about the fanclutch maybe be on it, But I have an electric fan. It heats to a point where the overflow tank shoots all the anti freeze out. The Temp gauge just goes above a bit over half the temp gauge. In other words it has not gotin hot enough to put the needle to the red spot. Just a liitle over the middle of the gauge. Then if I take of the resevore cap of, it starts to bubble and get full of antifreeze a all of a sudden the resevore gets empty. If I put the cap back on it kind of sucks the cap into place. I have noticed that I have had trouble screwing the cap back on. I have to push on it pretty hard and it seems to me that it is going on crooked. DOES ANYONE THINK I HAVE A T-STAT PROBLEM?

 

Try replacing the cap first. Sounds like you are not getting a good seal on the cap.

 

The cap on my 98 is fiddly, it does not want to seat properly. It looks like the oring is a bit swollen and a tight fit. I just pay special attention and push down firmly before turning.
It's hard to describe, but there is a different feel when it goes on properly, plus you can see it screwing down the threads.
Do your fans come on? Maybe that si a problem. Also, changing a thermostat is cheap and easy, you might want to give that a try.