What Is a Catch Can?

High horsepower and more notably BOOSTED engines create conditions in an engine that are not typically or ever seen in their factory form. Pressure built by faster moving engine parts, wider ring gaps, looser tolerances, and stresses on components can allow for crank case pressure to increase. Not allowing the excess crank case pressure out can cause even more issues including: seal failure, loss of horsepower, oiling issues, and even fire hazards as oil exits seals. There are two types of catch cans that exist, but only one truly is appropriate for high horsepower applications.

The lines from the valve covers act as an escape route for built up crank case pressure. This will knock the oil particulate out of the charge before it turns the corner and heads out of a small air filter at the top of the catch can.

It is important to note this is not a vacuum leak, crank case pressure is completely separate of the pumping side of the engine where your intake and cylinders are connected to.

What is the benefit of a catch can?

Oil catch cans are simple devices that can greatly benefit direct-injected engines. They prevent oil and other contaminants from causing buildup inside your engine’s intake manifold.

Why are catch cans illegal?

Although a catch can could help your car’s engine run well for a long time, modifying the PCV system is illegal since it’s part of the engine’s emissions system. If a technician were to see an oil catch can installed on your car while performing an emissions test, they may fail you on the spot.

Is a catch can really necessary?

It should be noted that oil catch cans are only really necessary for direct injection engines. Unlike other engines, direct injection engines do not have fuel regularly cleaning the valves and are therefore more likely to experience the formation of carbon deposits.

Does a catch can add horsepower?

An oil catch can doesn’t add any power or make any cool noises so it is often overlooked when modifying vehicles. However, a catch can will ensure you always have a cleaner intake tract free of oil, and help keep your engine running better for longer.

Your cars engine has a very intricate way of taking care of itself. For example, when oil blowby occurs, the engine is set up to recirculate the oil through the engine again, however, that can lead to power loss over time unless you install an oil catch can. But what is a catch can and is it illegal to install one in your car?

The end result is that your engine will have cleaner valves and combustion chambers over time. While smog laws can vary by state, it is typically illegal to install an oil catch in your cars engine bay, according to SmogTips.com.

Oil catch cans are simple devices that can greatly benefit direct-injected engines. They prevent oil and other contaminants from causing buildup inside your engine’s intake manifold. Here’s how they work, and why you might want to install one on your own car.

An oil catch tank or oil catch can is a device that is fitted into the cam/crankcase ventilation system on a car. Installing an oil catch tank (can) aims to reduce the amount of oil vapors re-circulated into the intake of the engine.

Not only was this more pleasant for the car occupants it also meant that oil mist was not released into the air or onto the road in the case of draft tube ventilation systems. During the normal operation of an engine the excess blow-by and oil vapors from the crank case are allowed to enter the intake system.

It will then begin to clog up the throttle body, swirl flaps , or even the intake valves on direct injected engines. Having a buildup of sludge can cause lower performance due to the limiting effect it has on the air flow to the engine.

What is oil blow-by?

In order to understand what an oil catch can is, you first need to know what oil blow-by is. In a typical four-stroke engine, there is an intake stroke, which lets the air-fuel mixture into the cylinder; the compression stroke, which compresses that air/fuel mixture; the power stroke, which is when the spark (from the plugs) ignites the mixture and forced the piston back into the cylinder; and the exhaust stroke, which is when the exhaust gas is pushed out of the cylinder.During the compression stroke, an immense amount of pressure is built up so much that a small amount of air can escape from around the piston rings. This is called “blow-by,” and the higher the RPM your engine spins, the more blow-by it will have. Fortunately, every engine has a PCV system that vents the crankcase – and the blow-by – and routes it back into the engine’s combustions chambers to safely burn them up.

Positive crankcase ventilation[edit]

During normal operation of a car engine, some vapors from the cylinder pass by the piston rings and down into the crankcase. Without ventilation this can pressurize the crankcase and cause issues such as lack of piston ring sealing and damaged oil seals.To avoid this, manufacturers created a crankcase ventilation system. Originally this was often a very basic setup where a filter was placed on the top of the cam case and the pressure and vapors were vented to atmosphere. This was deemed unacceptable as it allowed fumes and oil mist to be vented out into the atmosphere which caused pollution. It could also cause issues for the occupants of the car as it could be drawn into the inside of the car, which was often unpleasant.Around 1961 a new design was created. This design routed the crank breather into the intake of the car. This meant that the vapors and oil mist could be burnt and expelled out of the car through the exhaust. Not only was this more pleasant for the car occupants it also meant that oil mist was not released into the air or onto the road in the case of draft tube ventilation systems.

Problems caused by intake routed crank breathers[edit]

There are two issues that can be caused by routing the crank breather into the intake system of an engine.The main issue is with the buildup of oil inside the intake piping and manifold. During the normal operation of an engine the excess blow-by and oil vapors from the crank case are allowed to enter the intake system. The oil mist cools and layers the inside of the intake piping and manifold. Over time this layer can build up and thick sludge can accumulate.This has been made worse with the introduction of the exhaust gas recirculation (EGR) system on more modern cars. The oil vapors can mix with the re-circulated exhaust gasses and soot which then builds up on the intake manifold and valves etc. This layer over time hardens and thickens repeatedly. It will then begin to clog up the throttle body, swirl flaps, or even the intake valves on direct injected engines.Having a buildup of sludge can cause lower performance due to the limiting effect it has on the air flow to the engine. If the buildup becomes excessive on the throttle body it can cause poor idling as it can block the air flow whilst the throttle plate is shut.Fitting a catch tank (can) will reduce the amount of oil vapor reaching the intake tract and combustion chamber. Without the oil vapor the soot from the EGR valve will not congeal so much on the intake which will keep the intake from becoming clogged.

How a catch tank (can) works[edit]

An oil catch tank (can) is fitted in line of the crank case breather system. It is placed in between the breather outlet and the intake system. As the crank vapors pass through the catch tank (can) the oil droplets, un-burnt fuel, and water vapor condense and settle in the tank. This stops them from reaching the intake and causing the issues mentioned above.The best type of catch tank (can) will often have some sort of media inside such as a fine metal mesh or Brillo pad style metal which will create a much larger surface area for the vapors to condense.Over time the catch tank (can) will fill up with the excess oil and will need to be drained. This is often done by opening a drain plug on the bottom of the tank.