There’s no air vent in the radiator, otherwise it would leak. There’s a tube between the radiator’s neck (where the radiator cap attaches) and the overflow tank, do you mean that? I think you are referring to my post above. That’s the small air vent in the plastic overflow tank, usually in its lid.
Yes i was referring about your last post but i got your point
Sorry!
The expansion tank is only marked with “full” and “low” mark, maybe they are the cold and hot.