3tops,
From I read above, it seems that you get this T4 reading difference all along the power on of your machine.
As far as I know, arrius 2F has a so called t4 conformation box in order to homogenized the temperature reading. The value is given to the VEMD by means of a couple of resistors, slope and 0 adjustement. Did you try to check this box or the resistors as it could be the source of this trouble ?
My 2 cts
Bunka