Abstract: An oil filter including a filter housing, a cover and a filter element arranged within the filter housing and provided with an outlet channel which is closed by a seal when the cover is in a closed position and which allows oil situated in the filter housing to run out into a collecting tank when the cover is opened.

Abstract: A oil-fill opening 12 for introducing lubricating oil into an internal combustion engine provided with a cap 15 which has a bayonet lock. On the outside of the wall of the oil-fill opening there is an oil separator 22 through which the blow-by gases from the crankcase are conveyed to the intake manifold and/or to the clean-air side of the air filter. Oil collected in the oil separator 22 is returned through a return port 23, 24 between the oil separator 22 and the oil-fill opening 12. To prevent oil from getting into the oil separator when oil is poured into the oil-fill opening 12 and backing up therein so that under certain circumstances it reaches the clean-air side of the air filter, a shutter 25 in the form of a rotary slide valve, which covers the return port 23, 24 between the oil separator 22 and the oil-fill opening 12 when the cap 15 is removed, is provided within the oil-fill opening.