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Not sure who is right here but Gtxragtop (Dave) did a test on my dipstick tube to determine CCV function by measuring the amount of vacuum pulled (I can't remember but I think the proper amount is 3"-6" of water). Not sure where this test came from (TIS?). No/low vacuum meant a CCV problem. My understanding is this test measures the amount of vacuum in the crankcase. But I am not sure how the pressure in the sump translates to the pressure in the crankcase. According to this test, the sump should have negative pressure and pull on the balloon, if the CCV is functioning properly. If it inflates the balloon, there is definitely a problem as that would indicate positive pressure in the sump. In addition, positive pressure in the sump should also blow the dipstick out of the hole. In theory the CCV is supposed to keep the crankcase from a positive pressure condition and that a failed CCV will create a positive pressure situation by keeping the crankcase from venting gases. If I sound confused, it is because I am. :dunno: All I know is that I replaced the damn thing and I have stopped burning oil.
 

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In a nutshell, the crankcase always produces pressure from blow-by. The CCV is simply a "middleman" controlled by Intake Manifold Vacuum.
This way the positive pressure from the crankcase is removed by the CCV which separates oil and vapor:
- Oil goes back down the crankcase
- Vapor goes back into the Intake manifold.

This is why the CCV is also called "Oil Separator" in the Volvo language.
Got most of that. Someone correct me if I am wrong. I refer to the real.oem diagram for the CCV. The oil and vapor from the cylinder head (positive pressure) goes into the CCV through the vent pipe (2). The CCV "separates" the liquid from the vapor and returns the vapor portion back into the intake manifold (negative pressure) using the connecting line (3) and the return pipe (7). The liquid oil condensate flows back into the sump via the vent hose (4).

If the previous is correct, is the sump at negative pressure, ambient or positive pressure? The dipstick vacuum pressure test suggests it is at negative pressure.

I ask because my previous e39 (which Gtxragtop tested) tested OK for negative pressure even though the car demonstrated some of the classic symptoms of CCV failure (oil consumption, burning oil, etc.). My current e39 appeared to burn oil (occasional black exhaust smoke in cold weather) but was never tested. I changed the CCV and that has gone away. It would be great to have a reliable test to verify proper CCV function as it is a PITA to change out. At this point, I am not so sure the dipstick vacuum test is that reliable of an indicator.
 

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BB:

Your flow directions are correct except for the vacuum hose. The RealOEM parts diagram is INCORRECT. There is NO vacuum hose. When you remove your old CCV, you will see that the vacuum hose connector is capped and the new replacement CCV is also capped.
 

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Great explanation, RDL! In plain understandable English, too. The best description of CCV function and malfunction I have seen to date. #5 also explains why BMW enlarged CCV return on the dipstick tube. Thanx. :thumbup: :thumbup:
 
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