A see-through coolant container is not part of the pressurized system. What may you do while the engine is at operating temperature?
Correct answer: A – Check the level and remove the container cap to add coolant
The Rhode Island CDL manual permits the coolant level to be checked through a sight glass or see-through container while the engine is hot. If that container is not pressurized, its cap may be removed and coolant added at operating temperature. Never open the radiator cap or another pressurized cooling-system component until the system has cooled because hot steam and liquid can cause severe burns.
Source: Rhode Island Commercial Driver License Manual — § 2.14.1, “Engine Coolant”


