My 92 Legend Acura is Overheating... eventhough I've changed, the waterpump,...

[lsolidsnake1]

...radiator, hoses, thermostat.? why does it still keep overheating.... also, I put in a refurbished engine(just in case it was the head gasket)
also, i need to replace a part the is behind the waterpump (it think it's some kinda of sensor, but i don't know the name of this part)