Damage can occur to the engine if too much water is injected or if the injector itself malfunctions. Water is not compressible, and much water in the cylinder prior to, or during, the compression cycle can cause a condition called hydrolock, where the volume of liquid in the engine is close to or greater than the volume between piston and head (or between pistons in a opposed piston engine) of the engine at top dead center, resulting in extremely high cylinder pressure that may cause blown heads, shattering of the piston, connecting rods or other damage to the engine. This damage is normally fatal to the engine and typically requires a full rebuild or engine replacement.