Most likely cause is an airlock in the cooling system
More than likely an airlock in the cooling system, bleed the system and should be fixed.
Engine cooling system is not a closed system you can't remove the air.
To bleed air from the cooling system of a Fiat Cinquecento, start by ensuring the engine is cool and the radiator cap is removed. Run the engine with the heater set to maximum and allow it to reach operating temperature; this helps circulate the coolant. Once the thermostat opens, any trapped air will rise to the top of the system, allowing you to top off the coolant as needed. Finally, replace the radiator cap securely to prevent any further air from entering the system.
Engine cooling system is not a closed system you can't remove the air.
If it doesn't have a "bleeder" screw at the top of the thermostat housing--remove or loosen one of the heater hoses with engine running and at operating temperature and allow water to run for a couple of minutes If it has a "bleeder" screw--just open slightly and let vehicle runs for a couple of minutes
use to remove the air inside the system
The purpose of the AC drain pipe in a cooling system is to remove excess moisture that accumulates during the cooling process, preventing water from leaking or causing damage to the system.
Entire cooling system should be flushed to remove dirt, scale, rust and sediment buildup which will corrode and clog/ruin your engine/cooling system
The purpose of a condensation pipe in a heating or cooling system is to remove excess water that forms during the process of heating or cooling, preventing water damage and maintaining the efficiency of the system.
I'm not a mechanic but what I done on mine was when engine cool take radiator cap off turn heaters on full on hot, start car and let tick over, keep an eye on the coolant level as you will need to top up once air lock clears
Low engine oil can effect the cooling system as it creates additional friction which may be difficult for the cooling system to remove. The oil is designed to both lubricate and cool the internal components.