Greetings from the Queen City of the South. Allow me to say a few good words about your articles before I introduce my concern to you. We find your articles not only informative, but we also know that we readers of Top Gear are getting the right counsel to whatever quandary we get to experience from the cars that we own. On top of this, I can sense the effort made by you to make the discussion more comprehensible by explaining in layman's terms some technical words when deemed necessary to be mentioned.

Now, here's my concern. I recently purchased a BMW 320d. But I have gathered (I just don't know how accurate) that somewhere around the 100,000km mileage, the turbo may experience problem. If this happens, the replacement or repair of such will be irrefutably expensive. Having said this, may I ask how true this turbo problem is with a 320d or perhaps even with other turbodiesel engines?

What recommendations can you give that will protect the turbo and contribute to its longevity? More (horse) power to your daily endeavor and may your charisma never cease to grow. You might want to know that you already have a strong following here in Cebu.

Your truly,

Miguel de Guzman

Hi, Miguel. I don't know which specific 320d model you have, but a quick look at the available information and discussions regarding turbo failures on BMW 3-Series diesels indicates that the failures are more common in the M47TDU20 series of engines, particularly the 2002-2003 model years.

This series of engine was where BMW first implemented common-rail diesel technology for the 2.0-liter diesels. With it, there was also an increase in displacement to 1,995cc from the previous-generation M47TD20's 1,951cc. Balance shafts were also incorporated in the redesign--or technical update--of the engine to quell the vibrations inherent in larger displacement four-cylinder engines.

According to available information, what caused problems in this series of engine was the "swirl flap" mechanism. The swirl flaps were butterfly valves much like a throttle body plate, but located in the individual intake runners. Over time, the retaining screws which held the plates to the actuating rods would work loose and eventually find their way to the combustion chamber causing foreign object damage. There are also instances wherein the screws would be expelled from the exhaust manifold and cause damage to the turbine blades and housing. This problem was addressed by changing out the component to one-piece flaps molded from engineering plastic.

Another possible cause is the crankcase breather filter. I have no information as to which series this problem manifests itself in, but what supposedly happens is when the breather filter gets clogged, crankcase pressure rises and this "blows" out the oil past the turbocharger's shaft seal. The result, of course, does look like turbine failure to those unfamiliar with such a problem, and vehicle owners may potentially be charged the cost of a new turbocharger unnecessarily.

Turbochargers usually fail when the seals, bearings or bushings fail due to lack of lubrication or due to contaminants in the oil, which make their way to the seals, bearings or bushings that abrade the said parts. This abrasion causes parts to wear down much more quickly than they normally would given that turbine shaft speeds spin up t0 100,000rpm. Yes, that's 100,000rpm or more than 10 times than most high-performance street engine will ever spin.

A good oil--one that's rated to handle the higher temperatures that a turbocharged engine will encounter compared to a normally aspirated engine--oil filter, and air filter change interval is the best guarantee against premature turbine failure. While that may drive up the cost of maintenance somewhat, it should still be cheaper than the cost of an unnecessary and unwanted turbine replacement due to lack of maintenance.

Best regards,

Ferman Lao
Technical Editor

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