If the temp on your jeep just keeps climbing and never pauses around 200-210, it is almost certainly your tstat, like Israel said. The other possibility is a hosed water pump, although not as likely. Both have happened to me. One time I had a water pump go out without any warning at all, no sound, leaks, or anything. I also had a bad tstat that wouldn't open until about 230 or so, so the temp would quickly reach 230, then zoom back down to about 200 in about 5 seconds when it finally opened; not good.
If the problem just started happening, it likely isn't your radiator. Radiators in my experience don't just suddenly fail (unless they spring a leak), they just gradually lose effectiveness. I suppose with the Renix you could have a faulty pressure bottle, but that probably wouldn't show itself it the symptoms you have described.
It isn't hard at all to change the stat, I don't know about the Renix but my 94 just has 2 bolts that hold the tstat housing on, pop it off, remove gasket and tstat, put new one in, apply gasket maker to new gasket and bolt it back on. Not hard. I've seen shops actually charge anywhere from $40-70 (70!!:huh
. It took me 15 minutes the first time, 10 minutes now.
And get an OEM tstat!! They only cost 10 bucks or so and come with the gasket. Trust me when I say I've learned it makes no sense to use a lower temp stat or a cheaper non dealership tstat. Also, if the problem lies with your waterpump there is absolutely no reason to spend over $100 on a Flowkooler or some other "high-performance" one. An OEM style replacement is more than adequate. I have a stock or OEM replacement tstat, waterpump, hoses, and rad cap. The only "upgrade" in my system is a 3 row all metal radiator and my jeep always runs at 210. (I should add basic oem replacment fan clutch as well)