I said I will update on the results, and missed for few weeks, at the end the problem was the water pump that still had the plastic impeller and was already cracked. Must change.
The problem then was to find spare parts, at reasonable cost and availability.
Firts choice the specilized alfa mechanic in my area, but prices were far to high and offered a five weeks waiting time. ( Presently live in Guatemala - Central America), the Alfa dealer is the same of a Japanese brand, and no longer bringns Alfas to the country since several yers ago and their actual stock of spare part is very limited.
Through this page a saw some comments of Alfaworkshop.com on the uk and search their webpage; very easy to use, they had what I was looking for (took the oportunitty not only to purshase the water pump but other parts as well), had to contact them directly for specifics on the mailing address and they provided very fast support.
Long story short, purshased the parts via the Alfaworkshop webpage and in three days delivery time I had the parts delivered to my office.
I usually dont take the time of sending feedbacks of the service of companies were I buy things, but this guys have a very good overall bussiness setup through their webpage.
Hope this comment can be of used to other alfa owner.