I really hate to say it, but something very similar is happening to me....
In my case, It's definitely a bad head gasket.

You can supposedly buy a test kit at Napa for ~10$ that checks for combustion gases in your coolant.
How long after starting your car (from cold) does pressure appear in the upper radiator hose? If there's pressure appearing within a few minutes of starting, it's a bad sign. It'll be combustion gas pressurizing the coolant system.

Try adding pure antifreeze. My car initially had no white smoke because I was using nearly pure water after many aparent "overheats" while driving only a few miles. After adding antifreeze and burping the system, everything seemed fine - until I started it up later that day, it blew coolant out the reservoir, and started blowing white smoke (not with every engine pulse) out the tailpipe.

I sincerely hope it's NOT your head gasket, but I encourage you to get a test kit for exhaust gas in your coolant.

Best of Luck,
Will
--
1990 740 Turbo, on its way to stock specs, maybe beyond