normal operating temperature

The factory temp gauges arent calibrated or set so thar x sweep = y temp. It just shows a 'normal' range. As long as the gauge is in the normal area, youre fine. If you swap gauges but nothing else the needle may end up in a slightly different spot at the same temps. Swap sending units and you may see the same thing as it may send a slighltly different voltage at the same temps.

The reason your gauge shows a fast increase in temp and then stops is that is when your thermostat opens up. Until you hit whatever temp your thermostat opens at it doesnt allow coolant to circulate except in the block so it heats up quickly and runs corectly. Once the thermostat opens it regulates the flow through the radiator which maintains the operating temperature.

 

I'll add some data.

106 F ambient air temp. Hills and mountainous terrain. Engine temps between 195 F and 208 F

 

I just changed out my water pump, coolant (Toyota red mixed with distilled), and thermostat on my 3RZ. I also swapped in a new fan clutch even though the old one seemed fine when I removed it.

Before doing this, my normal operating Temp in city driving was around 194°. After doing this my normal operating temp was around 185°.

I am guessing that the coolant flush and thermostat made the largest difference. My coolant was about 60k miles old. The thermostat was most likely original at 175k.