Weird coolant heating issues but not overheating?

[Crowcifier6]

Thanks [MENTION=58830]JWaldz[/MENTION]. Motivation to try and bring my temps down. I saw 216F on my Scangauge II yesterday after driving around mid day. Outdoor temp was a mild 75F, quick run into the store (engine only off for <5mins.)

The heat sink effect, where the engine actually gets hotter after shutting down before cooling is where I see the highest temps, driving usually not over 197F.

Anyone have the 4 cylinder 3RZFE? Wondering how much coolant I'll lose just replacing the thermo...

 

[chewie]

Update

I tested two new Toyota thermostats, trying to see when they open exactly and at what temperature. Then pulled my existing for a third try.

**Jiggle valve found at 12 oclock**

Minor difference in one of the 3 which seemed to really open at 185°F while the others at 187-188°F. They all seemed to crack open at 183 and then would let out a little air bubble a couple degrees later which I felt was truly open. Anyways, it's pretty hard to tell any real details of the stove test other than if something were really wrong or faulty.
I did put in the "better" thermo but installed with JIGGLE VALVE at 6 O'CLOCK position and it made all the difference!

80+ degrees outside, I took a test drive over a bridge with a long 2.5 mile grade one way then back with a shorter but steeper grade the other direction. A/C on the whole time with a good load on the engine, the temp didn't go above 194°F giving me at least 10° cooler running temp.
I'm convinced the jiggle valve had everything to do with my issue of low 200° temps.
Thanks to this thread and others on this site, I shouldn't overheat randomly and probably helping preserve the life of my head gasket and ultimately the engine.

Hope this helps someone else!
****SCAN your temps in real time cause your cluster temp gauge won't tell you there is a potential problem!!!