A properly functioning crankcase ventilation system prevents internal pressure build-up, oil leaks and engine damage. The PCV system (Positive Crankcase Ventilation, a system that removes harmful gases from the crankcase and routes them back to the engine) prevents these gases from damaging the engine. Regular maintenance and timely replacement of hoses and valves are essential to avoid costly problems. Read on to discover why this often neglected component makes such a big difference.
What is crankcase ventilation and how does it work?
Crankcase ventilation keeps the engine healthy by removing blow-by gases (combustion gases that leak past the piston rings into the crankcase) from the crankcase. During combustion, small amounts of gases, water vapour and oil mist leak past the piston rings into the crankcase. Without ventilation, overpressure builds up that can damage gaskets and seals.
The PCV system routes these gases in a controlled way back to the inlet manifold. There they are burnt again, which contributes to cleaner exhaust and lower emissions. A faulty system disrupts this process and causes measurable problems.
In older models such as the Volvo V70, hoses can harden and passages can become blocked. Five-cylinder turbo and petrol engines in particular are prone to contamination of the crankcase ventilation system because of higher loads and temperatures.
Signs that your PCV system needs attention
A number of symptoms point to problems with the crankcase ventilation. These signals often appear gradually and are therefore easily overlooked.
- Oil leaks around the rocker cover, seals or sump pan
- Whistling or hissing noise from the engine bay
- Overpressure when opening the oil filler cap
- Dipstick that is hard to pull out or is pushed upwards
- Unstable idling speed
- Increased oil consumption without visible leaks
- Loss of power in turbocharged cars
A practical check is to test the crankcase pressure. Carefully open the oil filler cap at idle. A healthy engine shows a slight vacuum, not extreme suction or clearly blowing pressure. Strong overpressure often points to blocked crankcase ventilation.
Common causes of faults
The PCV system has several weak points that lead to problems over time. These causes occur especially often in cars with higher mileage or lots of short trips.
Blocked oil separators are a common problem. Oil mist and sludge build up in the separator, which restricts the flow. This in turn causes pressure to build up in the crankcase.
Rubber hoses harden due to heat and age. Small cracks appear, causing the system to draw in air or lose air. In turbocharged cars this process accelerates because of higher temperatures.
The diaphragm in the PCV valve can tear or deform. This disrupts the controlled discharge of gases. Contaminated narrow channels and connections block the flow. Some models have an infamous small passage that clogs up quickly.
How to maintain the PCV system
Regular inspection prevents many problems. At every major service, check the crankcase ventilation system for signs of wear and contamination.
Check hoses and connections
Inspect all rubber hoses for cracks, oil traces and hardness. Gently squeeze the hose. A healthy hose is flexible, not a rigid tube. Replace hardened or cracked hoses as a preventive measure.
Also pay attention to clamps and connections. Loose clamps cause false air or pressure leaks. Make sure all connections are tight and the rubber is undamaged.
Test crankcase pressure regularly
Measure the crankcase pressure with the engine warm and idling. Overpressure indicates blockages or defective components. Abnormally high vacuum can point to a blocked air supply or a defective diaphragm.
Clean or replace the oil separator
Some oil separators can be cleaned, others must be replaced. Consult your car’s service manual. In cases of severe contamination, replacement is often the most reliable solution.
Use the correct engine oil
High-quality engine oil of the correct specification limits deposits and sludge. Oil change intervals that are too long increase the risk of contamination of the PCV system. Stick to the prescribed intervals.
‘ More complex work such as replacing the oil separator requires more experience and sometimes special tools. ’
How long does it take to replace the crankcase ventilation?
The duration of a service depends on the type of car and how accessible the components are. In many models, replacing hoses and the PCV valve takes between 1 and 2 hours. More complex systems with integrated oil separators take more time.
In some engines the oil separator is located under the inlet manifold. Removing and refitting it then requires several extra hours of work. For such jobs, expect a workshop visit of 3 to 5 hours.
DIYers with technical insight can carry out simple maintenance tasks themselves. Replace rubber hoses and check connections with basic tools. More complex jobs such as replacing the oil separator require more experience and sometimes special tools.
What happens if you ignore maintenance
A neglected PCV system leads to increasing damage. First, small oil leaks develop at gaskets and seals. Overpressure pushes oil past seals to the outside.
If left untreated, this can escalate into larger leaks. Oil is forced out of the dipstick tube or oil filler cap. That contaminates the engine and can even pose a fire risk if it comes into contact with hot components.
Long-term overpressure damages seals and bearing shells. Replacing those is considerably more expensive than timely maintenance of the crankcase ventilation system. In turbocharged cars, oil leaks can damage the turbo, leading to costly repairs.
Internal contamination increases due to incomplete combustion of blow-by gases. This raises the risk of carbon build-up in the intake ports and on the valves. Engine performance drops and fuel consumption rises.
What does servicing the PCV system cost?
The costs vary per type of car and the scope of the work. Replacing rubber hoses and a PCV valve costs on average between 100 and 250 euros including labour.
In models with integrated oil separators the costs are higher. The part itself costs between 150 and 400 euros, depending on the brand. On top of that, count 200 to 400 euros in labour for removal and refitting.
Preventive maintenance is always cheaper than repairing consequential damage. A new seal or gasket quickly costs several hundred euros in labour and parts. Damaged turbo seals or bearing damage can run into the thousands of euros.
Invest in regular checks and timely replacement. In the long term that saves considerable repair costs and keeps the engine healthy.
‘ Unstable idling or strange noises can be early signs of crankcase ventilation faults. ’
Practical tips for a longer service life
Regularly drive longer distances with the engine at operating temperature. That helps to evaporate condensation and sludge, so the system becomes contaminated less quickly.
Avoid too many short trips. Cold starts produce extra condensation that does not fully evaporate. This accelerates contamination of the crankcase ventilation and oil separator.
Include the PCV system in your maintenance planning. Note down when you checked or replaced hoses. That helps you act preventively before problems arise.
Pay attention to changes in engine behaviour. Unstable idling or strange noises can be early signs of crankcase ventilation faults. Do not postpone a check if you notice anything unusual.
Discover more about car maintenance
Crankcase ventilation is just one aspect of good engine maintenance. On the Carnews website you will find extensive information about preventive maintenance, common car problems and practical tips for car enthusiasts. Discover more about how to keep your car in top condition and avoid costly repairs.
Frequently asked questions
Crankcase ventilation and the PCV system remove blow-by gases, water vapour and oil mist from the engine block so that no harmful overpressure develops in the crankcase. This keeps seals and gaskets intact, limits oil leaks and increased oil consumption and prevents oil from being forced out. A well-functioning PCV system also ensures cleaner combustion, smoother idling and preservation of power. Blocked or faulty components in this system can ultimately lead to serious engine damage and expensive repairs.
Common symptoms of a blocked or faulty PCV system are oil leaks around the rocker cover, seals or sump pan, unstable idling, increased oil consumption and sometimes a whistling or hissing noise from the engine bay. You often recognise it by noticeable overpressure or, conversely, strong vacuum in the crankcase: with the engine running, the oil filler cap clearly sucks or blows and the dipstick can be hard to remove or even be pushed upwards. The engine may also run less smoothly and in turbo engines you sometimes notice loss of power or less smooth turbo operation. As soon as you notice one or more of these signs, it is sensible to have the complete crankcase ventilation/PCV system checked.
Have the PCV system checked at every major service, usually every 20,000–30,000 km or once a year, depending on your service interval. In older cars or if you make lots of short trips, it is wise to have the system checked extra thoroughly and to replace hoses/diaphragm preventively around 150,000–200,000 km. In between, occasionally check yourself for oil leaks, strange whistling noises and obvious overpressure or strong vacuum when unscrewing the oil filler cap. If you see or hear anything unusual, have the crankcase ventilation/PCV checked immediately instead of waiting for the next service.
Yes, in many cases you can replace the PCV valve or clean parts of the PCV system yourself, provided you have some mechanical experience. You typically need: a basic socket set, screwdrivers, pliers for hose clamps and possibly a torque wrench. In addition, new hoses, clamps and possibly a new oil separator/PCV valve are recommended as replacement parts. Also make sure you have brake cleaner or a similar cleaning agent to clean contaminated channels and connections.
Ignoring PCV maintenance can in the long term cause overpressure in the crankcase, with oil leaks, increased oil consumption and even serious engine damage as a result. Due to contamination, hoses and passages become blocked, which can “push out” gaskets and seals and cause the engine to run roughly or lose power. A poorly functioning PCV system also leads to more oil mist and blow-by gases in the exhaust flow, which increases emissions of harmful substances. That not only worsens the reliability of your engine, but also the environmental impact of your car.