1) Easily passes 
when piston rings do not effectively seal combustion pressure, allowing hot gases to blow between rings and cylinder wall. This causes overheating of piston and poor performance.
Passage of unburned fuel and combustion gases past the piston rings of internal combustion engines, resulting in fuel dilution and contamination of the crankcase oil. See also: Piston.
leakage of the air-fuel mixture or of combustion gases between a piston and the cylinder wall into the crankcase of an automobile. · a device, fitted to a crankcase, for conducting such gases back to the cylinders for combustion.