What maintenance issue could cause a bus to overheat during operation?

Low coolant levels are a critical factor that can lead to overheating in a bus during operation. The cooling system is designed to maintain the engine at an optimal temperature by circulating coolant to absorb heat from the engine and dissipate it through the radiator. When coolant levels drop, there is insufficient fluid to effectively transfer heat away from the engine. This lack of coolant prevents the engine from maintaining a safe operating temperature, which can result in overheating, potentially damaging engine components and leading to costly repairs.

In contrast, while dirty fuel injectors can affect engine performance and efficiency, they do not directly cause overheating. Poor tire alignment may lead to handling issues and increased tire wear, but again, it does not have a direct impact on engine temperature regulation. Worn-out brake pads can cause braking inefficiencies but are unrelated to the engine's cooling system. Understanding the role of coolant levels in preventing overheating is crucial for maintaining the health and efficiency of a bus's engine.