Thanks guys for the information. I probably need to do some cooling system maintenance given the lack of documented maintenance on this bike. A system flush and new coolant at a minimum.
I guess the real question is can I/should I do something with that sensor to get the fans to kick in at a lower temp?
NO, YOU CANNOT ;-)
In my previous post, I had "indirectly" answered your question.
From my earlier post above:
"... Motronic ECU will start both radiator fans based on the data from a 2nd coolant sensor (located in rear most cylinder head. You cannot change this sensor for a different type (having a different resistance curve) as this sensor is also use to adjust mixture (injectors time) based on pre-programmed data in ECU tables."
MORE DETAILS to better explain my "NO, YOU CANNOT":
1) the K1200RS/LT coolant sensor (in cylinder head) has an inverse resistance curve: as temp go higher, the sensor has less resistance. This is a common automotive design for such sensor.
2) When the resistance of this sensor reaches 178 Ohms (+/- 5 error), the ECU assumes the engine is at 105 celcius (221 F) and will start both radiator fans. It will wait until the temp has come down to a specific point (about 260 Ohms / 194 F) to shut the fans OFF.
3) The same coolant sensor curve (each resistance matches a specific temp) is also used by the ECU to adjust Fuel injection mixture (injector time).
4) If you try to fool the ECU by adding OR removing resistance in this circuit you might be able to trigger the fans earlier, but you will also completely mess-up the injector time (mixture control).
There is a way out of this, but it requires implementing a separate temp sensor that would trigger the radiator fans RELAY (instead of letting the ECU trigger the same RELAY). This modification is not something that I would recommend unless you are very handy with electronics AND can take the risk to overheat the engine (if your modified system fails).
YOUR BEST BET is always make sure the cooling system is maintained / stays in good shape (rad fins, thermostat, fluid level , Rad-CAP, sensors...). Regulary confirm If BOTH rad fans start and stop at position outline earlier on gauge, check fluid level is stable in expansion tank (when cold).