Blow-by refers to the leakage of combustion gases from the combustion chamber past the piston rings into the crankcase. These gases contain unburned fuel, water vapor, and other byproducts of combustion. Diagnosing excessive crankcase pressure often begins by observing the presence and quantity of these escaping gases. Addressing this condition typically involves identifying the root cause, such as worn piston rings, cylinder wear, or a malfunctioning positive crankcase ventilation (PCV) system. The repair can range from simple component replacement to a complete engine rebuild, depending on the severity and source of the leakage.
The presence of excessive blow-by can significantly reduce engine efficiency and longevity. The contaminants entering the crankcase can dilute the engine oil, reducing its lubricating properties and accelerating wear on critical engine components. Furthermore, the increased crankcase pressure can force oil past seals, leading to oil leaks and potential environmental concerns. Historically, blow-by was a major contributor to air pollution, but the introduction of PCV systems has mitigated much of that impact, although proper functioning of this system is still paramount.
