In the diesel world, "blow-by" is a term you're bound to run across at some point if your line of work involves diesel-powered vehicles of any kind. What is blow-by, what causes it, and how concerned should you be? At Autoworks in Ithaca, NY, our fleet maintenance and diesel technicians see it on a regular basis. Here we'll take a quick look at blow-by, correcting it, and preventing it.
What is Blow-By? - Diesel blow-by is a term that describes an event of lost compression into the crankcase. Blow-by occurs whenever a burnt or unburnt fuel and air mixture escape from the cylinder and past the piston rings and into the crankcase. In a perfect world, the piston would be sealed tightly in the cylinder, able to move up and down but keeping all the air and fuel and exhaust that enters or exits the cylinder during the combustion process out of the crankcase. As you'll see, this perfect world doesn't exist, but it is important to minimize the amount of blow-by in a diesel engine.