clouds of grey smoke!

300tdi non edc auto, no egr, it will start and drive fine and then after about 20 mins there will be a smell of oil and then it will start to produce clouds of grey smoke with a faint smell of oil. But not as blue as You would expect if it was burning lots of oil. Pull over turn it off and start her back up and she will burp the last of the closeout of the exhaust and be ok for another 10/15 mins and do the same again. Any ideas? No visible smoke when idleing or if you rev it in neutral, unless it has already started its smoking thing then reving it will just make a bigger thicker cloud. Anyone got any ideas? On guessing a pressure buildup somewhere blowing oil past a deal?

What state is the oil breather in on the side of the rocker box?