When the positive crankcase ventilation system is working properly, there should be a slight vacuum inside the cam cover. When you put yout hand over the oil filler cap hole you should be able to feel it.

It's easier to use the oil filler cap itself - not so hot on the hand. Turn it so that it can come off, but leave it on - lift it gently and feel for the vacuum pullling it down.

From what you say, your Volvo will flunk that test.

Please say what year Volvo, and - if you know - what engine? The flame trap location changed on the North American model with the 1988 240.

If you prefer less work it's easier to replace the whole system, including the oil separator box, rather than cleaning it piece by piece. Should be way under $50 USD, and requires minimum skills and tools.

Good Luck,

Bob

:>)