the present invention relates to a cylinder head cover for covering a cylinder head of a combustion engine . such cylinder head covers often comprise an oil separator for separating oil and / or oil spray from the blow - by gas of combustion engines . with the present invention the oil separator is formed as a flow - through tube through which the gas with the oil and / or oil spray to be separated flows . the flow - through tube with its longitudinal axis in the flow - through direction lies essentially in the plane of extension of the cylinder head cover . a worm - like segment is arranged in the flow - through tube , and its thread surfaces form a spiral flow path . at the same time the cross section of the flow path lies between 1 mm2 and 800 mm2 .