Oil Change on a BMW 840Ci

The recommend oil is a quality full synthetic 5w40 motor oil. If you intend to keep this car you should change your oil every 6 months or 6k miles. Water builds up in your oil from daily condensation and will foul your crankcase ventilation system if it is not changed regularly. If you check around you will see that BMW has had a significant problem with there crancase ventilation systems failing in cold climates. This began happening after the crazy long oil change intervals came out. The failures in the crancase systems are fromn water freezing in the systems and breaking them. Keep in mind that automobile manufactures sell cars therefore have no interest in yuo driving your car for the 400-500 miles it can run. To speed up its detrioration they simply increase the oil change interval to plan failure in the mid 100k range.