Thread: CCV and oil pressure pondering
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Old 12-11-2011, 11:09 AM
taosx5 taosx5 is offline
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Quote:
Originally Posted by JCL View Post
To build on what twinspoppa posted, CCV refers to the crankcase ventilation system. The system includes vent lines from the valve cover, and performs the same function as a positive crankcase ventilation (PCV) valve. There is actually a valve in there, as it allows pressure to be released to the intake, while not flowing the other way at times of high manifold vacuum. BMW added an oil separator in to the system, to remove engine oil mist from the ventilation system. That is cleaner, environmentally, than burning the oil mist in the engine. The oil that is removed from the vented air flow is then returned to the oil sump. It is a fairly elegant system, except that in some models the separator is not mounted close enough to the engine to be kept warm, and it can freeze up.

There is usually condensation inside the engine due to heating/cooling cycles, but in the normal course of events it is boiled off when you drive. If the engine does not get hot enough, for a long enough period of time, that condensation will build up and eventually form an emulsified paste that collects under the valve cover. If enough of it builds up, it can collect in the crankcase ventilation system. That would still not be a huge problem, except that it has water in it, and so it can freeze if it gets cold enough out. If the valve in the CCV freezes in the closed position, then you no longer have a functioning crankcase vent, and crankcase pressure can build up. What will happen is that the pressure will push out past the weakest gasket, usually the valve cover gasket. On the other hand, if the valve freezes in the open position, then during times of high manifold vacuum oil from the sump can be drawn up into the intake manifold, potentially leading to a hydraulic lock if the oil makes it into a cylinder. That isn't common, but if it does happen, it can be catastrophic.

So, this is not related to the oiling system (except that separated oil is returned to the sump).

I don't know how similar the 4.6 is to the 4.4, and it varies slightly from year to year as well, but the principles are the same.
Thanks JCL, I sort of understood the concept but this really helps. I guees in other threads I read and pictures I had seen it must have been the older valve you mentioned because it was flat and came apart in two pieces displaying a rubber gasket that could be replaced. I wil do more reading and see if there is anyone with a similar problem on the 4.6. In my case the oil is definitely coming from the top of the oil filter cannister. I suspect that is the weakest link you describe. I appreciate your help.

I am on a road trip right now in the wife's 4.4 dealing with a mystery head lamp issue that I described in another thread. Thanks again.
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