If you've ever wondered “does a diesel engine have a PCV valve?”, the short answer is yes – diesel engines generally have a crankcase ventilation system, although it may not always be called a traditional PCV valve.
On BMW diesel engines, the system is commonly referred to as the crankcase ventilation (CCV) system, crankcase breather or oil separator.
Its job is important: it controls pressure inside the engine crankcase and separates oil from crankcase vapours before those gases are routed back into the engine's intake system.
At Bimmer Garage Nottingham, we specialise in BMW and MINI diesel servicing, diagnostics and repairs, including crankcase ventilation, turbocharger and engine problems.
What Is a PCV Valve?
PCV stands for Positive Crankcase Ventilation.
During normal engine operation, a small amount of combustion gas can pass the piston rings and enter the crankcase. This is known as blow-by.
Without a crankcase ventilation system, pressure would continue to build inside the engine.
The ventilation system allows these gases to be controlled and routed away from the crankcase.
On many diesel engines, the system also contains an oil separator designed to remove oil droplets from the crankcase vapour.
Do BMW Diesel Engines Have a PCV System?
Yes.
BMW diesel engines use crankcase ventilation systems, although the exact design varies between engines.
This applies to popular BMW diesel engines such as:
- N47
- N57
- B47
- B57
The system can include components such as:
- Crankcase breather
- Oil separator
- Breather diaphragm
- Breather hoses
- Ventilation passages
The exact design depends on the engine generation.
What Does the BMW Diesel Crankcase Breather Do?
The crankcase ventilation system has several important functions.
It helps to:
- Control crankcase pressure
- Remove blow-by gases
- Separate oil from vapour
- Return separated oil to the engine
- Route gases back into the intake system
A properly functioning system helps prevent excessive pressure and reduces the amount of oil entering the intake.
BMW Diesel PCV Valve Problems
A problem with the crankcase ventilation system can produce several symptoms.
Possible signs include:
- Excessive oil consumption
- Oil around the intake system
- Increased crankcase pressure
- Oil leaks
- Whistling noises
- Rough running
- Excessive smoke
- Turbocharger-related symptoms
These symptoms can also be caused by other engine faults, so the PCV/CCV system shouldn't be blamed without diagnosis.
Oil in the BMW Diesel Intake
Seeing some oil in the intake system isn't necessarily abnormal on a turbocharged diesel.
Crankcase gases can contain oil vapour, and some of this can enter the intake system after passing through the ventilation system.
However, excessive oil accumulation should be investigated.
Possible causes can include:
- Crankcase ventilation problems
- Excessive blow-by
- Turbocharger oil leakage
- Worn engine components
- Intake-system contamination
The amount and location of the oil are important when diagnosing the problem.
BMW PCV and Turbocharger Problems
The crankcase ventilation system and turbocharger can sometimes be confused because both can result in oil appearing around the intake.
If a BMW diesel has excessive oil in the intake, the turbocharger should also be assessed.
Possible turbocharger symptoms include:
- Blue smoke
- Increased oil consumption
- Loss of boost
- Whining noise
- Poor acceleration
- Excessive oil in the intake
A turbocharger should not automatically be replaced simply because oil is found in the intake.
Can a Bad PCV Cause Oil Leaks?
Yes, excessive crankcase pressure can contribute to oil leaks.
If the crankcase ventilation system isn't controlling pressure correctly, pressure can build inside the engine.
This can place additional stress on seals and gaskets.
Possible symptoms include:
- Oil around the engine
- Oil leaks from seals
- Oil around the rocker/valve cover area
- Increased oil consumption
The source of the leak should still be identified rather than assuming the PCV system is responsible.
BMW Diesel Crankcase Pressure
Correct crankcase pressure is important for engine operation.
Too much pressure can indicate a ventilation problem or excessive blow-by.
Too much vacuum can also indicate that the ventilation system isn't operating correctly.
A technician can test the system rather than relying only on visual inspection.
BMW N47 PCV / Crankcase Breather
The BMW N47 2.0 diesel uses a crankcase ventilation system designed to separate oil from crankcase vapours.
If you're experiencing oil in the intake, excessive smoke, oil consumption or unusual breather noises, the N47 crankcase ventilation system should be included in the diagnosis.
However, N47 owners should also consider the condition of the:
- Turbocharger
- Intake system
- EGR
- DPF
- Engine seals
These systems can produce overlapping symptoms.
BMW B47 PCV / Crankcase Breather
The B47 replaced the N47 in many BMW applications.
It also uses a crankcase ventilation system, although the design and component arrangement differ from the N47.
If a B47 develops excessive oil consumption or intake contamination, the crankcase ventilation system should be checked alongside the turbocharger and engine condition.
BMW N57 PCV / Crankcase Breather
The N57 six-cylinder diesel also uses crankcase ventilation and oil-separation technology.
Because the N57 is a higher-output six-cylinder diesel, diagnosing excessive oil consumption or intake contamination should include the complete ventilation and turbocharging systems.
Does a BMW Diesel PCV Need Replacing?
There isn't one universal replacement interval for every BMW diesel crankcase ventilation component.
Whether it needs replacement depends on:
- Engine type
- Vehicle mileage
- Service history
- Component condition
- Symptoms
- BMW service recommendations
If the system is functioning correctly, replacement isn't necessarily required simply because the vehicle has reached a certain mileage.
What Happens If You Ignore a BMW PCV Problem?
Ignoring a crankcase ventilation fault can potentially lead to further problems.
Excessive crankcase pressure may contribute to oil leaks, while excessive oil entering the intake can cause additional contamination.
If the problem is related to the turbocharger rather than the PCV system, continuing to drive the vehicle could also allow the turbo fault to worsen.
This is why correct diagnosis is more important than simply replacing the breather.
BMW Diesel PCV Diagnosis Nottingham
At Bimmer Garage Nottingham, we can investigate BMW diesel crankcase ventilation and oil-related problems.
Depending on the symptoms, checks can include:
- Inspecting the crankcase ventilation system.
- Checking crankcase pressure.
- Inspecting breather hoses and connections.
- Checking for excessive oil in the intake.
- Inspecting the turbocharger.
- Checking for oil leaks.
- Checking engine fault codes.
- Assessing related EGR and intake-system problems.
This helps determine whether the problem is actually the PCV/CCV system or another engine component.
BMW Diesel PCV Problems – Bimmer Garage Nottingham
So, do diesel engines have a PCV valve? Yes, diesel engines generally have a crankcase ventilation system, although BMW commonly uses terminology such as crankcase breather, CCV or oil separator rather than simply calling it a PCV valve.
If your BMW diesel has oil in the intake, excessive oil consumption, smoke, oil leaks or unusual breather noises, don't assume the PCV system is automatically at fault.
Contact Bimmer Garage Nottingham with your BMW model, year, engine and symptoms.
We can diagnose the crankcase ventilation system and check the turbocharger, intake and related engine components before recommending the appropriate repair.
Bimmer Garage Nottingham – BMW & MINI diesel specialists in Nottingham.