blow by is the piston pressure which escape from rings into the cylinder and comes out from the oil cap ,,,,,the same as what we see in petrol engine breather,,,,,,,,,in desil engine you have to open the oil cap and check for blow which is leaking from the piston rings ,,,,,,,,
engine oil which you see when you remove the tappet cover ?,,,,,,,,,,,if its accumulating there and not travelling back to the oil sump ?........if its so them it some time happen when mechanic change the engine gas kit ,,,,,,,,the passage is blocked by the small holes of new after market gas kit , which must be broadened , i usually even broadened the water holes as well ,,,,,,,,,,,,that small pipe is i guess breather pipe , as what we see in petrol engines but without PVC valve ,,,,,,,,,,,,,early moring white smoke is a sure sigh of oil buring oil inside cylinder either leaking from piston rings or intake valves, in most cases its from the intake valve seals and they can be easily changes without doing any open heart surgery ,,,,,,,,,,,
try doing the blow by test early moring ,,,,,i am sure you will see white smoke emitting from engine oil cap ,,,,,,,,,,