There is a lot of white smoke coming from my 2004 520i exhaust about 1 or 2 minutes after start up and then goes away after 4 or 5 miles driving. It billows out on idle. It seemed to get worse over the winter months. I'm just wondering if it's just condensation from the exhaust or something more sinister. I have no apparent coolant/oil loss or any running or idle problems and only occasional light sludge on the underside of the oil cap which disappears after a long run.

The car is left idle for a couple of days in the week and used for a few short trips too as well as long ones.

Should I be concerned?

 

I wouldn't be concerned. It sounds like condensation, that eventually dissipates as you drive. If you had a real problem, that white smoke wouldn't stop and it would most likely be a coolant issue.

 

My 535ix has done that before after sitting for a while. White smoke stops after a couple miles. I'm not losing any coolant or burning any oil so I'm thinking it's just condensation. As long as your fluid levels don't go down I wouldn't worry too much.