Been about 6 weeks now (87 Renix update). Yesterday we got back up to about 95 F ambient, >90% humidity, and I got stuck in mid day traffic for an extra hour of crawling traffic on 33 mile trip. AC on Max, no problems. Renix bottle with Volvo cap is holding up nicely. Coolant temps unchanged, and the 16 lb cap on the inline filler neck has never opened or vented as I theorized, renix coolant bottle is still 1/2 full, unchanged, so my closed/open Renix mutant hybrid cooling system is working perfectly. Holding 180-200 F at the thermostat housing for 60 F to 95 F ambient days. Note my thermostat is 180 F.
Summary of relevant changes I made. Installed a new CSF 3 row Brass/copper radiator, new 97 parallel flow AC condensor on the R-12 converted to R-134a AC, new ZJ (grand cherokee standard FC) fan clutch, new standard water pump, and new POS plastic Renix Coolant bottle with a Stant brand Volvo bottle cap on the Renix bottle.
I have also determined that my renix is indeed running leaner, and thus hotter, which is why I had to clean up and make improvements to the cooling system. In spite of the 1 hour traffic jam and poor mileage I still got a 15% higher mileage on the last tank of gas than I got anytime in the last 4 years. I have had a bout 20% increase in mileage since my renix started running hotter.
Also note worthy is that just before it started running hotter I replaced the harmonic balancer. The jeep sat up for 4 weeks during that time. When I started it back up it had a terrible, very load valve train noise, much worse than valve-tappet-lifter noise I had gotten use to the last 40,000 miles and 4 years. So I did a trick that 5-90 taught me that had worked to some extent the last 9 months, which was to run the RPM in park up to 3500 and hold it for a minute to free up the stuck lifters. Well ever since I did that the last time, just after replacing the HB, the 4 year old lifter noise (always worse in cold weather, and first days start up) has been gone completely, and the engine runs hotter, and leaner, and gets better mileage ever since that day.