Blow-by 101: What is Blow-by and How to Keep it from Ruining Your Engine

Blow-by 101: What is Blow-by and How to Keep it from Ruining Your Engine

Introducing Blow-by and the PCV System

Internal combustion engines are essentially controlled bombs; air and fuel combust to drive pistons and crankshafts.  One byproduct of this violence is power, but there are darker horses to contend with.  During combustion, high pressure on the top side of the piston pushes combustion gasses, as well as droplets of oil and fuel, past the piston rings and into the crankcase. This mixture is known as "blow-by."

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Many modern vehicles use complex PCV systems to vent blow-by from the crankcase.

To keep the crankcase from becoming pressurized, causing issues with oil sealing and robbing the engine of power, blow-by is pulled from the crankcase via the positive crankcase ventilation (PCV) system and routed back into the intake. 

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