During the filling of a coolant system, who is correct regarding the handling of the engine venting petcock and the after-cooler petcock?

In the context of filling a coolant system, Technician A's approach is correct as it emphasizes the importance of venting the engine and after-cooler petcocks to ensure that all air is expelled from the system. Proper venting is crucial because trapped air can create hot spots, reduce the efficiency of the cooling system, and lead to engine overheating. During the filling process, opening these petcocks allows any trapped air to escape, ensuring that the coolant can flow freely throughout the entire system without air pockets.

In contrast, any methods suggested that do not involve venting these areas correctly can lead to improper coolant circulation, making it difficult to achieve the optimal cooling performance of the engine. Therefore, the emphasis on correctly handling the venting petcocks as outlined by Technician A plays a significant role in maintaining the efficiency and safety of the diesel engine's cooling system.