Crankcase Ventilation | What does a Crankcase Ventilation do?

Crankcase ventilation is the safest system for the environment, as it does not allow harmful gases to come out of the engine or the fuel chamber. In this article, I will discuss the full details of Crankcase Ventilation.


Crankcase Ventilation.

Crankcase Ventilation

Crankcase ventilation system also known as Positive Crankcase Ventilation. So the crankcase ventilation system has many advantages and disadvantages also. Mainly this system is introduced to the Automotive Industry just to save the environment from the harmful gases coming out of the engine combustion leakage. 
The production of combustion contains mainly nitrogen, water, and carbon dioxide, Sulphur acid particles may also be present due to Sulphur content in the fuel. The product of combustion may leak through the piston rings into the crankcase. The gasoline also finds its way into the crankcase oil by slipping past the piston rings. Thus, the lubricating oil in the crankcase becomes dilute when mixed with water and gasoline which leaks past the piston rings.
The acid causes corrosion of the crankcase metals as does water, if either or both are allowed to collect and remain in the crankcase. The crankcase ventilation removes all these unwanted particles from the crankcase which leak past the piston rings. It prevents the lubricating oil from being diluted, and the corrosion of crankcase metals due to acid formation.

How does a Crankcase Ventilation System Works?

How does a Crankcase Ventilation System Works?
Crankcase Ventilation Diagram


The crankcase ventilation is used in automotive engines. It consists of phasing through the crankcase a constant stream of air which picks up and carries away most of the fuel vapor and water vapor before they can condense out and dilute the lubricating oil.
Air is drawn into the crankcase through the breather cap and is discharged through an outlet tube at the side of the engine. As you showed it on FIg. The circulation of air in the crankcase takes place due to the motion of the vehicle,, the moving piston, and the fanning action of the crankshaft. Some designs use additional filtered air inlet in the crankcase to supply the air. 
The PCV valve is a crucial component in the system. It is usually a one-way valve that controls the flow of gases between the crankcase and the intake manifold. When the engine is running, the PCV valve allows the intake manifold to draw gases from the crankcase.

Why do Engines Need Positive Crankcase Ventilation?

In positive crankcase ventilation, the crankcase vapor is returned to the engine through the intake manifold, instead of being exhausted into the atmosphere. The crankcase outlet tube is connected to the intake manifold just beneath the carburetor so that the vapors are drawn into the intake manifold and utilized by the cylinder during the operation. 
Over the normal crankcase ventilation system, the positive crankcase ventilation system is safer and more prominent towards nature. In the PCV system, the excess gas that comes out from the exhaust is not safe, but for the engine, this excess is a rich mixture for better combustion in the engine. 
In BS-4 engines the positive crankcase ventilation system is installed. When a driver needs more acceleration this excess gas helps the system.

What Causes Excessive Crankcase Pressure?

Excessive crankcase pressure means, in the compression stroke the combustion pressure or the burst of the a/f mixture is more than the specific. This excessive pressure can cause engine damage or the moving parts can be damaged. The reasons behind these excess pressures are –
  1. Piston rings are the reason for the selling effect between the piston and cylinder wall. If the piston rings get clogged or worn out then the combustion gas can lead to the crankcase causing excess pressure. 
  2. If the PCV valve gets clogged then the whole ventilation system will fall down causing the pressure in the engine.
  3. If the engine temperature is too high then the blow-by gas will increase that goes to the engine crankcase, this will cause crankcase pressure.
  4. If the bearings, the piston rings, or the cylinder liner gets damaged then the gases or the combustion will go to the crankcase.
  5. If the engine oil level is too high then the excess pressure can happen in the crankcase.


If the engine design is too poor, or the engine is designed in an inappropriate manner then the combustion pressure causes the engine excess pressure.

What Happens if Crankcase Pressure is Too High?

In an engine(IC engine) the engine power is generated through a specific manner. If there are any malfunctions then the power generation will be hampered. Crankcase pressure can cause several damages to the engine. These are –
  1. High crankcase pressure can lead to oil leaks that can damage the engine parts. 
  2. If the oil leaks then the corrosion can lead into the engine.
  3. The engine performance can be hampered because the excess pressure can damage the PCV system. 
  4. The fuel economy of the vehicle will be hampered because of the improper and leaking of the combustion pressure.
  5. This excessive pressure damages the PCV system, causing pollution in the environment.
  6. High crankcase pressure can cause the oil to foam, reducing its lubricating properties. Inadequate lubrication can lead to accelerated wear and tear on engine components.
  7. The engine sealant and the gasket can damage due to excessive pressure.
  8. If the PCV system is clogged then the engine misfiring can cause.

What are the Benefits of a Crankcase Ventilation?

Crankcase ventilation system serves several crankcase ventilation systems. The main reason to bring this system into the engine is to serve the environment. These benefits are – 
1. Emission Control – The crankcase ventilation system brings the excess gases containing harmful gases into the cylinder and saves the environment. 
2. Oil Preservation – This system preserves the oil safely and doesn’t allow the engine oil to mix with the water and the combustion gases.
3. Engine Efficiency – It helps to provide better engine efficiency, by maintaining a balanced pressure, the PCV system can contribute to improved engine efficiency, better fuel consumption, and overall smoother operation.
4. Increase Engine LIfe – If the dilution of the oil does not happen in the engine then the engine lifespan can increase because of no corrosion happening into the engine.
5. Save the Engine Moving Parts – If the malfunction does not happen then the perfect combustion of the engine can lead to no damage to the engine moving parts. 
Many countries have strict emission standards for vehicles. A properly functioning PCV system ensures that the engine meets these standards, allowing the vehicle to be legally registered and operated on public roads.


The crankcase ventilation system helps to improve engine performance, fuel economy, blow-by gas, and many other engine operations.
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