An oil catch tank or oil catch can is a device that is fitted into the cam/

crankcase ventilation system A crankcase ventilation system (CVS) removes unwanted gases from the crankcase of an internal combustion engine. The system usually consists of a tube, a one-way valve and a vacuum source (such as the inlet manifold). The unwanted gases, called ...

on a

car A car, or an automobile, is a motor vehicle with wheels. Most definitions of cars state that they run primarily on roads, seat one to eight people, have four wheels, and mainly transport people rather than cargo. There are around one billio ...

. Installing an oil catch can aims to reduce the amount of oil

vapor In physics, a vapor (American English) or vapour (Commonwealth English; American and British English spelling differences#-our, -or, see spelling differences) is a substance in the gas phase at a temperature lower than its critical temperature,R ...

s re-circulated into the

intake An intake (also inlet) is an opening, structure or system through which a fluid is admitted to a space or machine as a consequence of a pressure differential between the outside and the inside. The pressure difference may be generated on the ins ...

of the engine.

Positive crankcase ventilation

During normal operation of a

car engine An internal combustion engine (ICE or IC engine) is a heat engine in which the combustion of a fuel occurs with an oxidizer (usually air) in a combustion chamber that is an integral part of the working fluid flow circuit. In an internal co ...

, some vapors from the

cylinder A cylinder () has traditionally been a three-dimensional solid, one of the most basic of curvilinear geometric shapes. In elementary geometry, it is considered a prism with a circle as its base. A cylinder may also be defined as an infinite ...

pass by the piston rings and down into the

crankcase A crankcase is the housing in a reciprocating engine, piston engine that surrounds the crankshaft. In most modern engines, the crankcase is integrated into the engine block. Two-stroke engines typically use a crankcase-compression design, res ...

. Without ventilation this can pressurize the crankcase and cause issues such as lack of

piston ring A piston ring is a metallic split ring that is attached to the outer diameter of a piston in an internal combustion engine or steam engine. The main functions of piston rings in engines are: # Sealing the combustion chamber so that there is mini ...

sealing and damaged oil seals. To avoid this, manufacturers created a

. 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

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 In internal combustion engines, exhaust gas recirculation (EGR) is a nitrogen oxide () emissions reduction technique used in petrol engine, petrol/gasoline, diesel engines and some hydrogen internal combustion engine vehicle, hydrogen engines. ...

(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 A throttle is a mechanism by which fluid flow is managed by construction or obstruction. An engine's power can be increased or decreased by the restriction of inlet gases (by the use of a throttle), but usually decreased. The term ''throttle'' ha ...

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 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.

Possibility of knock caused by excessive oil vapor

Another issue that has been raised as a possible problem with allowing oil vapor into the intake is the chance of pre-detonation (Knock) caused by the oil vapor exploding during the compression cycle of the engine. This has become more of an issue as more and more cars have started to run high boost levels and high compression ratios. The higher the compression and boost the more likely the oil is to start to burn (Pre-Detonate) Fitting an oil catch can in the breather pipe will stop the oil vapors from reaching the combustion chamber. This will reduce the knock effect.

How a catch can works

An oil catch 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 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 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 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.

References

{{Reflist Automotive technologies