False oil temp readings

[rolex]

This started back in summer,on the warmest of days starting the engine from cold I would get an oil temp reading of -2/-3 degrees. Now the weather has cooled down but certainly not freezing yet, average startup reading is -8. This is annoying as giving the engine just a few revs sets the alarm off. Does anyone know if there is a seperate oil temp sensor on the engine or is this controlled by the ECU?