sensors can be faulty but check the obvious too, plenty of cooling systems are partially blocked / coolant pumps knackered.
bubbling and spitting doesnt sound a good sign though if you've bled it, ive had this from coolant flash-boiling in the engine due to lack of circulation (fried water pump) and other time from partially blcoked radiator and stuck thermostats.
This would be true if the sensors were located in the same place. However, the fan switch is on the core of the rad and the temperature probe is by the stat.magg wrote: So fan switch thinks H is 90 degrees or temp gauge thinks 90 degrees is H. Someone must be wrong. .
If theres a lack of circulation / blockage then hot water from the engine will reach the stat housing first as its in the block and report a high temp. Without proper cirulation it can take a while for water to move around the rad and trip the fan switch.
My CBR250 had the same issue, gauge would be running up near the H mark but fan wouldnt cut in until it was just getting over H, I assumed it was faulty sensor and ordered a new one, same thing. pulled water pump flushed everything.
replaced a lot of stuff and chased in circles, flused engine with high pressure hose and rad too, turned out the rad was partially blocked.. the middle section of the core remained cold, this was close to the fan switch too.
New rad and runs in the lower 1/3 of the gauge now.
Think I'll stick to riding my 'Blade. No dramas with that one. 
