Originally Posted by Jokey
... When I touched the radiator inlet and outlet tubes, the inlet tube was warm but the outlet was cold (so was the radiator itself). This could be a broken water pump, but I'm guessing not, just because I didn't see many posts on it.
Has the clutch cover ever been removed on this bike? If so, it is easy to crack the water pump driven gear (plastic on 2000+ SV650) if not aligned properly during reassembly.
I agree with Svracer2, it is not the thermo switch, something is preventing coolant flow. Check low coolant, thermostat, blocked passage, or broken water pump/gear.