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.
To remove an airlock from the cooling system of a Honda Civic, start by ensuring the engine is cool and then locate the radiator cap. With the cap off, run the engine until it reaches operating temperature, allowing the thermostat to open, which helps circulate the coolant. You can also squeeze the upper radiator hose gently to encourage trapped air to escape. Finally, top off the coolant if necessary and replace the radiator cap.
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
To remove airlocks from a cooling system, start by ensuring the engine is cold and the radiator cap is off. Run the engine with the heater set to maximum to allow coolant to circulate, and periodically squeeze the upper radiator hose to help dislodge trapped air. If necessary, use a vacuum filler tool to help evacuate air from the system. Finally, check the coolant level and top off as needed to ensure proper circulation.
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
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