thanks for the answer!
I will try to find a cap locally to see it today.
Like you say there might be some bigger trouble in the way. I explain what happened:
Arriving home after 500 km, the temperature rises quickly(2 marks above 90 ºC), the radiator fan in second speed, tried the heater and not heating! Quickly parked and turned off the engine. No coolant in the expansion tank!
On the next morning I do a better inspection, take the cam belt covers. There was coolant dropping behind the water pump pulley.
Next, I send the 147 to the workshop (AR dealer) telling them what happened. I also ask that they change the pump and the timing belt (don't have 60000 mile yet but I just noticed on car maintenance book that they have 7,5 years).
After the job is done, the mechanic told me that I should take a good look on the temperature gauge. They noticed some marks of coolant around the expansion tank cap, meaning that the cap is not good (they didn't had caps) or, there is to much pressure building up in the cooling system, due to a possible head gasket leak and it could have been the major culprit of the coolant loss.
driving home (50 km):
- no overheating
- no white smoke
- the oil color is OK
Going to find a cap first. If it doesn't work, going to ask for a compression test on the cylinders.