Blow-By can be found on any engine type. It is a serious problem that can drastically affect the performance of an engine. When a Piston and a Cylinder Wall have an imperfect seal, the air-fuel mixture can leak into the crankcase of the engine. This can lead to engine Contamination or even a more-serious buildup of Carbon Deposits. Basically, Blow-By causes an engine to run inefficiently and can affect oil consumption, efficiency, power, and torque.