The "Catch Can" Explained
Added Aug 22, 2011, Under: Engine,General Automotive
Modern engines feature a variety of emission control devices and systems to reduce the toxic gases released into the atmosphere. One of these is called the Positive Crankcase Ventilation (PCV) system. During the combustion process a small amount of gases leak or “blow-by” the piston rings and create a positive pressure in the crankcase. The PCV system vents these gases along with oil mist from the crankcase and routes it back into the intake manifold so it can be burned off. The problem is, over time the excess oil vapor collects along the inside of the intake tract and forms a “gunk”. This can lead to a variety of issues including carbon build up, retarded timing, detonation, and power loss.
An oil-air separator is an aftermarket device that will condense and collect the oil vapor before it has a chance to reach the intake system. As the gases and oil vapor enter the can they typically pass through a screening mechanism that gives the oil vapor something to adhere to. As the droplets form they drop harmlessly into the bottom of the reservoir so that they can later be drained. The other gases are allowed to pass through so that they can be burned off as intended. These devices are often referred to as “catch cans”, though that term is truly more accurate when describing a fluid overflow tank designed to just capture leaking or overflowing fluids.
When it comes to selecting a catch can you will get what you pay for. Cheap catch cans (less than $100) are plentiful but they are often little more than an empty can with two ports. These will capture a small amount of oil but the vast majority passes straight through. Be sure that the can is designed to be opened so that it can be periodically drained and cleaned.