So I visited just another Alfa Service, though, it was a very reliable one. It isn't cheap but as I said - very reliable. I should pay but I didn't. Why? I'll try to explain in a while.
The head, headgasket, gases, fuses, oil, coolant - everything is just all right. The thermostat was also checked. They checked the lambda as well. They plugged in a computer and there it is so right.
They couldn't, however, do the drive-around trip because they didn't have enough time. Checking my car lasted about 3hours.
They said I should change the radiator. I said I'd changed it but it was a used one. I have to use a brand new this time.
Hence, because they checked everything and it seemed all right, they said I didn't have to pay for checking alfa as they hadn't solved the problem. Wow.
-When I change the radiator and the problem still persists I should go back and leave the car. They'll do the drive-around trip with computer. Dunno whether that makes any difference or not but is it really the radiator which has been troubling me for so long?