Which of the following engine conditions would be the likely cause of a tensile failure of a connecting rod?

A tensile failure of a connecting rod typically occurs when the forces acting on the rod exceed its material strength. Engine overspeed is a condition that can dramatically increase the speed of the piston and the associated forces within the engine. When the engine operates at excessively high RPMs, the inertia of the connecting rod and piston assembly can generate extreme tensile forces that can lead to the failure of the connecting rod.

The mechanics of a connecting rod involve not just the forces due to combustion pressure but also the inertial effects during operation. At higher speeds, the tensile forces from acceleration can exceed the design limits of the connecting rod material. Therefore, in cases where an engine has overspeeded, it is likely that the connecting rod would experience tensile failure due to these elevated forces. This makes engine overspeed a critical factor in contributing to the potential for such a failure.

Other conditions like high cylinder pressures and prolonged lugging can create stresses as well, but they usually manifest in different types of failures rather than purely tensile failures. Prolonged engine idling would not typically contribute to tensile failure, as the forces involved are significantly lower than those experienced during overspeed conditions.