if you had thermostat issues the coolant in your rad would be cold and the coolant in your engine would be boiling, there are 2 ways to test a thermostat, one if to run the bike and as it warms up feel the 2 rad hoses, one will warm up before the other, and then when the engine gets to running temp the thermostat will open and the temps will get close to even, the other way is to remove the thermostat and boil water in a pan, when the water is boiling, place the thermostat in the water and the centre section should open, if not you have a thermostat issue