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 WORKING CLASS AUTO AND DIESEL in Pell City, AL, 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.