What should be done to detect a possible hydraulic lock in a large engine prior to starting it?

To detect a possible hydraulic lock in a large engine prior to starting it, manually pulling the propeller through by hand for several revolutions is the most effective method. This technique involves turning the propeller in the direction of the engine's rotation. If there is a hydraulic lock, which occurs when fluid, typically oil, is trapped in one or more cylinders, the engine will resist turning, or it may become difficult to pull through, indicating that there is a problem.

This method directly addresses the potential issue because hydraulic lock prevents the pistons from moving normally due to the presence of incompressible fluid in the combustion chamber. By performing this check, a technician can identify a condition that could lead to severe engine damage if the engine were to be started without addressing the issue.

Other options, while they are standard procedures in engine maintenance, do not specifically address the need for checking hydraulic lock. For instance, draining the oil may be part of an engine maintenance routine, but it is not a direct indicator of hydraulic lock. Checking the spark plugs for moisture does not directly indicate a hydraulic lock either, as moisture can be caused by several factors unrelated to fluid intrusion in the cylinders. Closing fuel valves is a safety measure that prevents fuel from entering the engine but