Hi Andrejw, About the two speeds of the coolingfans, that is new to me and the first time to hear of it , but you never know it's Ferrari, infact I even try it on my own 308GTB but no results, so no two speeds of the fans.
There is a airbleed valve on your thermostatic-house, you have to bleed it
so that the air fully comes out your system. I'm sure you did this but anyway.
You overrulled the thermoswitch and it was ok'e, but you have to check if the fans are working when your engine is hot. The radiator cap opens on 0,9 kg. 308ROB