If the coolant overflow container is not part of the pressurized system, to check the coolant level,

If the coolant overflow container is not part of the pressurized system, you can remove the cap to check the coolant level even when the engine is hot. Alternatively, some vehicles have sight glasses to let you check the coolant level. Note: Never attempt to remove the radiator cap or any other part of the pressurized system until the system has cooled thoroughly. While it's hot, pressurized steam or boiling water can spray out and injure you.