OK, I just bought a '99 XJ 130K and emmaculate... but it overheats going up long grades, at one point it threw the radiotor cap and boiled off (replaced cap)... the next time it got above 220ish, but i pulled over and let it cool before taking off again a few times... (but it idles all day @ 210*)
So this Saturday i'm flushing with Napa 1400 and replacing the:
Fan Clutch
Water Pump
T-Stat
All in accordance with the helpful posts from y'all

i'll be headding up Sponner again (to Lake Tahoe from Carson City) on Sunday... I'll re-post with results.

 

So, I've read just about every post on XJ overheating issues. that's why i went ahead and replaced all the components in the cooling system except for the radiator... I took the XJ on a wheeling trip up to Hobart Reservoir on Sunday for a fishing trip with a Buddy, this Jeep did the clmb FLAWLESSLY! If there were further issues with the cooling capability they wouuld've reared thier ugly head, of this I'm sure.
the HD fan clutch is a must, thanks to all of you with this advice. and if you're one that's not yet sold on the idea... DO IT... it works!!
and by the way, it appears the T-Stat and Pump were Original, there were large cavitation pits on the back of the impeller blades, the T-Sat looked normal, but I didn't test it. I took my time, paid attention and did the swaps in about 5 hours...

 

Just did the HD fan clutch on mine, with the 160 tstat she doesnt get hot ever now, glad it worked for you too