What is blow by?

Blow by is a condition in which combustion gases leak past the piston rings into the crankcase of an internal combustion engine. This can occur due to worn piston rings, cylinder walls, or valve seals, allowing pressure from the combustion chamber to escape into the crankcase.

Blow by can result in a variety of negative effects, including reduced engine performance, increased oil consumption, and contamination of the engine oil with combustion byproducts. It can also lead to increased emissions, as unburned fuel and exhaust gases are released into the environment.

To diagnose blow by, a compression test or leak down test can be performed to check the integrity of the piston rings and valves. If blow by is detected, the engine may need to be rebuilt or repaired to prevent further damage.

Preventative measures for blow by include regular maintenance, using high-quality oil, and avoiding high engine speeds and heavy loads that can increase pressure in the combustion chamber. If blow by is detected, prompt action should be taken to address the underlying issues and prevent further damage to the engine.