Hi Edsway
From the 2011 date of your van I am guessing this is the Fiat "Comfort-matic" or "Selespeed" 6 speed transmission. This is a robotised M40 manual transmission, and as such has the same high efficiency as the manual version. You should not therefore be generating enough heat in the transmission to need a separate transmission oil cooler. A clutch temperature monitor is inbuilt, but as far as I know Fiat have not seen fit to monitor the oil temperature which suggests they don't consider it an issue.
Much more recently Fiat have changed to a 9 speed transmission which operates on traditional torque converter automatic principles. I believe this is a variant of the ZF HP9 unit, as also fitted to other vehicles e.g. Jeeps. In the interests of efficiency, modern automatics often "lock-up" the torque converter when cruising, to reduce losses and therefore heat generation. If this transmission is what you have, you could contact the ZF agents DA.MET in Salisbury, Queensland and ask their opinion.