A specific type of automotive engine damage occurs when water enters the engine and is compressed in one or more cylinders.

Figure 1 illustrates the damage sequence often called hydrostatic lock. The left drawing shows water entering a typical automotive engine cylinder during the intake stroke. Water, unlike the fuel/air mixture, is incompressible and, during the compression stroke, locks the piston in place as shown in the drawing at the right of Figure 1. This condition tends to overload the connecting rod, causing a bending failure of the rod and severe engine damage. A common way for water to enter the engine is driving through water sufficiently deep enough to allow injection into the air intake system of the vehicle, such as crossing a flooded road.

Figure 2 shows a failed connecting rod that sustained hydrostatic lock. After stalling in a flooded street, the vehicle operator started the engine, which suddenly failed. In this case, the connecting rod bending failure resulted in a fracture through the cross-section of the connecting rod. Figure 3 is a view of a connecting rod that sustained a hydrostatic lock bending failure without a fracture.