blowby

[pearce trucking]

Combustion of fuel air mixture occurs in the combustion chamber. The piston rings are in contact with the cylinder liner to seal the heat energy released during combustion and force the piston downward. Blowby is when some of the combustion escapes between the rings and the liner and into the crankcase beyond, thereby releasing some of the energy that would otherwise be used to force the piston downward. If you remove your oil filler cap, you will see a small amount of crankcase gasses escaping. Some small amount is acceptable, but not much.