Crankcase Ventilation System On Your BMW: Why It Matters And How You Can Know If It Is Failing

Your BMW is a driver's dream, but ownership involves a commitment to regular maintenance and a willingness to endure an occasional repair. Like any vehicle, BMWs have their own specific mechanical quirks that can be frustrating for owners. One such common issue involves the crankcase ventilation system; this system is an essential part of your BMW's engine operation, so a breakdown can keep your car parked in the garage. Below is more information on what the crankcase ventilation system does, how you can know when it is failing, and what your technician will do to address the problem:

What the crankcase ventilation system does

In your BMW, combustion gases from the rapid burning of gasoline force the piston down into the cylinder. The piston and cylinder are an extremely close fit, but there is still a tiny amount of gas leakage from the cylinder; these gases flow past the connecting rods and into the motor's crankcase. These gases accumulate inside the crankcase, and like a balloon filling with air, the internal pressure rises. Ultimately, the pressure will increase to an intolerable level, and your engine will relieve itself by blowing gaskets and seals and create expensive damage all the way around.  

Fortunately, the crankcase ventilation system (CCV) in your BMW is designed to eliminate crankcase pressure. This system, which is both simple and straightforward in design and operation, bleeds exhaust gases into the intake manifold, where they are reintroduced into the cylinders for additional combustion. In addition, the CCV removes oil vapor from the exhaust and recycles the collected oil condensate back into the vehicle.

How you can know when the crankcase ventilation system isn't working properly

The CCV on your BMW consists of five major components: a valve that controls the flow of gases and separates oil from the air and four hoses that connect everything together. A failure within any of these parts can lead to trouble with your BMW's motor functioning.

Like most engine concerns, a failure of the crankcase ventilation system will manifest itself by presenting one or more signs. Here are some you should look for:

  • Oil consumption – this is the most-prevalent symptom of a failing CCV system. Malfunctions within the system can cause oil-saturated gases to be carried into the motor and passed along to the cylinders. The oil will burn away in the cylinders, and you will notice a steady decrease in your oil levels. Problems such as this a testament to the importance of checking your engine oil frequently.
  • Excessive smoking – a car that produces blue or gray smoke is also a candidate for CCV failures; blue or gray smoke is a classic sign of oil being mixed with gasoline inside the cylinders. This is further confirmation of a failure to separate oil from the exhaust gases.
  • Abnormal air movement sounds – if you hear sounds that are best described as wheezing, whistling or honking, suspect a failure within your CCV.
  • Oily spark plugs – the spark plugs on a vehicle experiencing CCV failure are often coated with a layer of engine oil. Routine maintenance can help discover this problem, so be sure your spark plugs are checked, cleaned and replaced as recommended.

Two frequent problems that cause crankcase ventilation system failure

Now that you understand the symptoms, you should know more about the causes. In BMWs, there are two specific problems with the CCV that have appeared on a more frequent basis than normally expected: water/oil clogs and cracked or torn hoses.

Water condensation can be a problem for some BMW engines, particularly in cold weather conditions. The condensate forms inside the CCV valve and mixes with the oil droplets. This creates a dull yellow "gunk" that clogs the valve and prevents it from operating correctly.

As for the CCV hoses, it is common to find brittle hoses within the system; these hoses readily crack and break, and this creates a number of other problems such as those described above. All four hoses are susceptible to this problem of brittleness.

What can be done

For-all-but the most ambitious and well-equipped do-it-yourself mechanics, the repair of a CCV problem is best handled by professional technicians. There are several hours of work involved with the repairs, and replacement of CCV parts involves tricky maneuvering underneath the hood. The standard solution for CCV failure is replacement of the valves and hoses; even if the hoses are still intact, it is best to replace all four at the same time as the valve. This ensures you won't have to worry about another CCV failure soon after leaving the shop. Go to websites for more information on how to best take care of your BMW.