Bad Oil Separator Symptoms: Don’t Be Ignored

A good oil separator job is maintaining crankcase venting during all operating conditions. Also, A bad oil separator is a problem that most drivers face due to the car’s engine type. Likewise, a faulty oil separator can cause the motor to run rough. You may hear a whistling sound from the oil separator.

A higher-than-normal crankcase vacuum can cause crankshaft oil seals to leak outside air into the crankcase. You also can hear whistling noises from the front or rear seal areas at idle because of the bad oil separator. If you are rare with automobile parts, you may not catch the problem. But you need to recognize the problem of oil separators. However, let’s know the bad oil separator symptoms to indicate the problem in detail below.

Bad Oil Separator Symptoms

What Is an Oil Separator In A Car?

If you are new to the automotive world, you should learn about the function of an oil separator. Let’s briefly discuss what oil separators are in a car.

Actually, the oil separator’s job was once managed only by the positive crankcase ventilation (PCV) valve. Both parts work to prevent oil mist from entering the environment. Compression and machine temperatures have been boosted because of current technological improvements and modifications in the industry. As a result, oil separators’ popularity has also expanded. Nowadays, it works alongside PCV in innumerable automobiles.

Besides this, it can remove oil from the crankcase steam and return it to the system. Moreover, it operates by directing the blow-by-gasses through a baffles or filter series. This slows down the gas’s speed, and the oil mist does not condense. Then, the system can collect oil droplets and return them to the crankcase. Also, the oil separator controls the oil flow and steam by allowing steam to enter at precise times. Yet, it will also shut down the systems under specific engine loads.

Bad Oil Separator Symptoms

When experiencing oil separator problems, you may notice the following symptoms. The bad oil separator symptoms of diesel are:

Too Much Smoke

Some smoke from your BMW and Audis exhaust pipe is not a problem. But more smoke is not suitable for your car. Excessive smoke can blow by, resulting in engine piston firings. Too much smoke is also a bad oil separator symptom, Ford.

Usually, a positive crankcase ventilation (PCV) valve and oil separator prevent oil mist that comes from blow-by. But if they don’t work adequately, oil mist leaves the car’s system through the exhaust, causing smoke. Some car models may have blue smoke from the exhaust because of old oil separators.

Smell of Burning Oil

When oil mist exits from the oil separator, it can ignite elements outside the PCV system, like the engine outside. Typically, it produces a burning oil smell. Even a little burning oil can cause a strong odor.

Increased Oil Consumption

An oil separator works to return blow-by oil to the oil sump, resulting in less oil consumption. In contrast, if it doesn’t work correctly, some oil can be lost, boosting oil consumption. For that reason, you will need to change your oil more frequently.

Check Engine Light

Before your car, the oil separator can notice the problem. If there is any problem, it triggers the check engine light.

Although not all vehicles can diagnose the actual problem with your oil separator, various accumulated faults occur. These can include cylinder misfires, oxygen sensor/mixture adaptation errors, or fuel trim errors.

Oil Gunk Builds Up

Problems with your oil separator can cause oil caking around your engine’s various parts. These parts include the piston rings, cylinder head, and cylinder walls. This buildup can be dangerous to your machine, and if you don’t check, it can cause a loss of engine performance.

Whistling Noise

Due to an insufficient oil separator vacuum, the crankcase vacuum becomes higher than regular, resulting in whistling or screeching noises. Unfortunately, if the problem is terrible, you can hear the noise like a freight train pulling into the station.

Sludge Under Your Oil Cap

If your Audi’s oil separator system fails, it can’t remove all moisture from the oil returning to the oil pan. That moisture can accumulate under your oil cap, leaving a thick sludge behind. Additionally, if you see this sludge while checking the cap, you should immediately visit a service center. Lastly, this is also a bad oil separator symptom, Audi.

Rough Idle

Rough idle is the other BMW bad oil separator symptom. You will notice that your car shakes and bounces while idling rough. Mainly, it will be accompanied by odd noises. Hence, you can expect a rough idle since a bad oil separator messes with the crankcase vacuum.

Bad Oil Separator Symptoms VW:

A suitably functioning PCV system is crucial to how well your engine runs. Symptoms of an oil separator system manifest in various ways; you can quickly diagnose some than others. Symptoms are:

  • Vacuum leaks
  • Illuminated check engine light
  • Rough idle
  • High oil consumption
  • Inactive regulation code
  • Whistling sound from the engine cover
  • Lean and misfire codes P0300 and P0171
  • Oil leak from the rear main seal
  • Illuminated oil pressure light

Therefore, symptoms of the oil separator system can start to show at any time. Nonetheless, many people begin noticing oil separator symptoms around 60,000- 80,000 miles.

Bad Oil Separator Symptoms VW

Air Oil Separator Problems:

An air-oil separator changes your oil quality and separates the air from it. Unluckily, if this air oil separator doesn’t work correctly, starts to malfunction, or fails completely. Then, it can cause oil to build up around the piston rings and cylinder walls. This can significantly affect the combustion efficiency and exhaust processes.

In other words, if it starts to fail, it can severely affect other engine components. Ergo, your car will lose functionality and suffer performance. It would help if you correctly take care of your vehicle by professional automakers. Indeed, you should follow a routine maintenance schedule to keep up with regular oil changes and inspections.

PCV Oil Separator:

PCV oil separator will help expand the performance of your engine. Generally, it will hold extra oil and keep it out of your intake tract. For that, you can breathe cleaner intake air. In particular, PCV oil separators come with small and large body sizes.

The larger bodies provide better capacity and the bottom drain with an elbow that drains collected oil virtually. They are polished billet aluminum bodies, chrome, powder-coated, and painted. This small oil separator unit delivers a 2-piece body that unscrews for drainage.

Crankcase Oil Separator:

An oil separator for crankcase ventilation includes a housing with a lower end and an upper end. The lower edge communicates with the crankcase, and the upper edge transmits with the exhaust system. The accommodation typically extends from the bottom end toward the top end.

A first-stage filter component is disposed of near the lower end, including a relatively coarse pore first filter media. And, a second-stage filter component is disposed of near the upper edge and upstream of the first-stage filter component. The second stage filter component includes a second filter media with relatively finer pores than the first.

Oil Separator Replacement Cost

Since a bad oil separator can cause countless problems, it’s best to repair it immediately. Thus, the replacement cost of oil separators is about $10 to $1,800.

FAQ (Frequently Asked Questions)

Q. How do I know if my oil separator is bad?

If your oil separator can’t work correctly, you should find out why. After noticing some symptoms of this problem, you know you have a bad oil separator. When you see the first sign of your bad oil separator, you should repair it immediately. Otherwise, you have to spend a lot of money on the big failure of the oil separator.

Q. What happens when an oil separator fails?

When the oil separator fails, the primary results are safe. But if you ignore it for a long time, it can cause engine damage. If this tool is not working correctly, it won’t separate the oil from the “air.” Mainly, this matter isn’t good for the engine and can damage your spark plugs and catalytic converters.

Q. Can you drive with a bad oil separator?

Automobiles come with a turbocharged and direct injection called an air oil separator or oil catch can. For many people, these words may sound like foreign words. In particular, this part was launched in auto engineering to expand engine performance. People who have a performance vehicle may be concerned. It’s because if they drive with a bad oil separator, their car will face big engine damage.

Final Word:

Symptoms associated with bad oil separators are reasons for all drivers to be concerned. Every driver must be alert to their automobile behavior, including troubling engine problem signs. Eventually, since bad oil separator symptoms can cause other problems, you should take your car to the mechanic.

Please don’t ignore any signs of a bad oil separator when you notice them. To avoid any catastrophic problem, regular engine inspection is essential. We hope you can know the signs of bad oil separators after reading our blog post. So, when you notice any symptoms, please fix them immediately.


I am Engr. Z Eusuf Lubricant Specialist, Mechanical Engineer & has been working with engine lubricants for a long time and knows what makes them work best. I can help you find the right oil for your needs, and I have tips on how to keep your engine running at its best.