Catch cans can sometimes be inadequate for capturing oil vapors and blow-by from the crankcase of an internal combustion engine. Over time, these vapors can accumulate in the engine bay and decrease performance by clogging up intake valves, reducing fuel economy, and increasing emissions. Additionally, catch cans that are not properly maintained can become clogged with dirt or other debris which will further reduce their effectiveness at capturing oil vapor.
In short, catch cans are only effective if they are regularly maintained to ensure they remain clean and free of any contaminants that could impede their operation. If neglected or improperly installed, a catch can may fail to capture all of the unwanted oil vapor from an engine's crankcase—resulting in poorer performance and increased emissions levels for your vehicle.