Every once in a while, my Boxster, which has a flat 6 engine, will emit a cloud of oil smoke when starting. Completely at random. Makes no different how it was driven before parking up - or if on a hill etc.
Seems this is normal behaviour. But haven't heard a plausible explanation as to why. Especially why only sometimes. It uses little to zero oil - still reading full after 5000 miles.
Cracked diaphragm in the oil separator unit is a possible. According to this bloke:
Mine does the same. My BMW R1100S also does it.
I think it's because the oil doesn't drain back down the bores when you stop the engine.
It's a characteristic of horizontally-opposed engines. As you say, occasional and seemingly at random.
Only one side of the engine can be draining oil that's splashed into the cylinder towards the sump. So some can very slowly make its way past the rings.
John
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