Meaning of blow-by

blow-by

Pronunciation: (blō'bī"), [key]
— pl. -bies.
  1. leakage of the air-fuel mixture or of combustion gases between a piston and the cylinder wall into the crankcase of an automobile.
  2. a device, fitted to a crankcase, for conducting such gases back to the cylinders for combustion.
Random House Unabridged Dictionary, Copyright © 1997, by Random House, Inc., on Infoplease.