+ 1 to all responses!
Yet, some ThermoBob devotees insist the ThermoBob enhances engine cooling, although the manufacturer does not. After the thermostat opens, the engine is at the mercy of airflow and coolant circulation, ThermoBobbed or not.
The excursion of your temperature gauge needle appears quite normal; as dealership personnel often say, "They all do that!" (This time, the statement is true. Engine coolant heats up, thermostat opens. If coolant gets sufficiently hotter, thermal switch activates fan. Fan circulates additional airflow about radiator, coolant remains at safe operating temperature. As coolant temperature drops (e.g., from bike motion airflow), fan shuts off; cooler still, and thermostat closes. Repeat.)
CAUTION: Opinion follows--If Kawasaki had chosen to install an "IDIOT LIGHT," versus a temperature gauge, with the otherwise identical cooling system on KLR650s . . . much less motorcycle forum discussion would have appeared on this subject!
I wired a 12-volt dashboard light (a "jewel") from a constant "hot" wire to the thermal switch lead on my KLR250 (same fan circuit as Generation 1 KLR650s); when the fan kicks in, I can see the reassuring glow from this indicator telling me the fan relay has been activated (versus looking at the fan blade, or letting the fins clip the tips of my fingers). I also wired in a manual switch, permitting manual activation of the fan, but . . . that mod is of no significance, with a functional thermal switch, IMHO.
I personally know of no maintenance issue traceable to the stock KLR cooling system, operated within safe limits. YMMV!