Overheating!
My '96 overheated consistently when driven hard or slow in very hot weather (>95 degrees). The fans worked (tested mechanical fan via factory manual test, verified 219 degree set point for auxiliary fan), waterpump worked, thermostat worked, radiator did not seem to be occluded, no obvious source of the problem. It has been solved (99.5%, anyway) with the following fixes, in order from most important to least:
Very helpful
180 degree thermostat vs. 195 stock
Manual switch for aux. fan
Proping up the back of the hood 1" to allow hot air out
Getting into low range immediately when headed off road to keep the fan speed up, even if low range is not needed by the terrain
Slightly helpful
High flow water pump from ? (cant recall, but the "good" one)
Running 42% glycol (the minimum allowed--sometime try straight water or water with only a radiator cleaning agent for 60 minutes, it is stunningly better at heat transfer than water/glycol--too bad I can't run straight water all the time!)
High flow thermostat
Questionable at best
GDI three core radiator (luckily, my old one sprung a leak just when I decided to change it out, so I don't feel bad about this being a nonproductive change)
High flow thermostat housing
FYI, I was not impressed with the GDI radiator--there have to be better units than this out there. But it has worked OK for the last 18 months.
Some say that running a low temp thermostat is not good for losts of things on the xj, maybe they are right, but I had no choice. I have taken to partially covering the radiator when on road or in cool weather in an effort to run closer to 195. Then just uncover when going off road or it gets hot.
Rick