Q: Smoke from drivers side tail pipe on 2005 BMW X5

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My X5 has smoke that comes from drivers side tail pipe only. It doesn't appear to happen all the time though. Sitting at idle it will sometimes after driving for a while. Also if sitting at idle and then revved up smoke will bellow. I'm concerned that there is a lower engine issue and need some advise from someone that knows this 4.4L V8 engine. My mechanic says that it is because of a suction valve that needed to be replaced and that now there is oil in the converters that needs to burn out. I don't buy that story because after 800 miles it is still doing the same. I am currently monitoring to see if there is oil consumption which should help to prove or disprove this theory. I would appreciate anyone who can provide a little insight.
(1) Answer
If it is white smoke, it may be related to the valve stems leaking. I recently took two X-5s to a shop to have them inspected before buying them. Both had white smoke coming out of the tail pipes, but only on occasion, and while sitting idle and reving the engine. The tech stated it could be the valve stems leaking. The repair cost was 4k.