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Ian in San Antonio - BMW 740il Smoke on Start-up


Having just listened to this week’s show online, I heard Ian from San Antonio call in asking about a cause and remedy for some smoke upon starting his BMW 740il.

Tom and Ray agreed that it might be stuck piston rings due to sludge build-up based on infrequent oil changes given the car’s previous life as a leased vehicle.

There could be one other, substantially-cheaper-to-repair cause. These vehicles are equipped with an oil / air separator, which is the BMW equivalent of a Positive Crankcase Ventilation valve, or PCV valve. The purpose of the oil / air separator is to vent crankcase gasses, but by directing them into the cylinders for combustion rather than venting them directly into the atmosphere.

What might well be occurring in Ian’s case is that, due to the infrequent oil changes, the diaphragm located inside this separator is fouled with oil build-up or sludge, which is allowing raw oil to be pulled into the intake manifold, thereby causing the blue smoke at start-up. It only does so briefly inasmuch as the vacuum in the engine then cleans enough of the built-up debris off of the diaphragm such that it can close and prevent any more oil from being pulled into the intake.

The part number is 11 61 7 501 563, and it is called (in BMW terms) the “intake manifold end cover.” Obviously, this repair will not be cheap, as the terms “cheap repair” and “BMW” are mutually exclusive, but it won’t be nearly as expensive as a head gasket or engine rebuild, and can in fact be done by someone who is mechanically inclined.

Anyway, hope this helps and, along with this info, a ton of great information can be found on, a site by BMW E38 enthusiasts for BMW E38 enthusiasts.

Good luck, Ian!


Douglas, AZ