yes u have to drain the coolant to change the thermostat. well, unless u wanna get really messy lol in general the thermostat is working is the lower and upper radiator hoses are about the same temp with the engine running, not saying it couldnt be bad, but its just a tell tale sign that it could be a thermostat, or air in the system, or blockage, or all sorts of stuff...so i guess that wasnt much help then lol