Smoke...smoke everywhere.

[40cpe]

Overfilling the crankcase by a little won't cause the smoking. You are loosing compression by the rings or valves. It gets into the crankcase and has to go out somewhere. Driving at a little speed, the road draft tube creates a vacuum to exhaust the gasses out the bottom.

The compression rings can be worn or stuck and the oil rings still do their job reasonably well.

[Cecil/WV]

Smoke out the oil fill is usually caused by ring blow by.