When driving downhill, which of the following should be done to prevent engine damage?

When driving downhill, lowering the speed to below maximum rpm is essential for several reasons related to engine performance and safety. When a vehicle descends a hill, gravity increases its speed, which can lead to the engine overrunning and potentially exceeding the safe rpm limits. Operating the engine above its recommended maximum RPM can cause excessive wear and tear, overheating, and even catastrophic engine failure.

By managing the vehicle's speed to remain below maximum RPM, you ensure that the engine operates within its optimal range, allowing for better control of the vehicle and preventing the risk of engine damage. This approach also helps maintain better braking performance since relying solely on the engine to control speed can strain the braking system and create additional risks during a descent.

In contrast, coasting out of gear downhill may lead to losing control of the vehicle, while limiting downhill speed to lower than minimum rpm could hinder acceleration and handling. Stopping frequently can also disrupt the flow of driving and may not be practical or safe in many situations. Thus, managing speed relative to the engine's maximum RPM is the most effective way to prevent engine damage while driving downhill.