Michigan Commercial Driver's License (CDL) Practice Exam

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Why is it important to drain air tanks in a commercial truck?

To reduce the weight of the vehicle
To improve fuel efficiency
Your brakes may fail due to the water freezing
To allow for proper engine cooling

The correct answer is: Your brakes may fail due to the water freezing

Draining air tanks in a commercial truck is crucial primarily because the presence of moisture can lead to serious braking issues. When condensation builds up in the air tanks, water can accumulate and eventually freeze, particularly in colder temperatures. This frozen water can block the air lines and impair the functioning of the air brake system, leading to brake failure. Properly draining the air tanks eliminates this moisture, thereby maintaining the reliability and safety of the braking system, which is essential for safe driving. The other options focus on factors that are less directly related to the immediate operational safety of the vehicle. For instance, while reducing weight and improving fuel efficiency are important considerations, they aren't the primary reasons for draining air tanks. Proper engine cooling is also essential for vehicle performance, but it is not impacted by the air tanks in the same way the braking system is. Hence, the correct focus is on the safety of the brakes, particularly concerning the potential for freezing water in the air system.