Why is a CCV required?
 

I know its function is to relieve excess blowby in the crankcase, but why is the CCV arrangement required to maintain a slight vacuum?

My previous E30/M42 and E30/M20 only had a hose going from the valve cover to the throtle body (before the throttle plate), and the excess blowby was sucked into the engine.

Why do modern BMWs require that CCV? Would it be ok to simply run two hoses from the 2 cylinder head covers into a 'Y' and route it to the throttle body or intake tube?
I don't have my X5 yet, but never had that problem on my E46, even in cold canadian weather, but it seems to be more frequent on the X5, so, if the CCV could be deleted it would save a lot of troubles...

You wouldn't just need a hose, you would need a PCV (positive crankcase ventilation) valve, essentially a one-way vent valve that has a variable opening or restriction. It is calibrated to the engine's operation, ie how much vacuum there is in the intake manifold.

PCV valves still need to be maintained. They can get gummed up, and blocked, exactly the same as a CCV. The consequences are the same as with a blocked CCV.

I remember my old american cars. They had that PCV valve. But I'm 99% sure that my two E30s didn't have a PCV valve nor a CCV. There was a sheet metal plate under the valve cover to keep oil from splashing directly into the hose, and that hose was going to the throttle body.
The X5 draws the fumes into the intake manifold, which is under vacuum, and the possibility of sucking oil is there, in the event of a torn diaphragm. By going to the intake tube, which is at atmospheric pressure, this could not happend.
May be I'm missing something. I will study the system more when the X5 will be in my driveway :D

i think the real story is that the ccv is cheaper to manufacture then the pcv valve

i believe either will work, and as stated both need maintenance

I don't think a CCV valve with an oil separator is cheaper than a PCV valve.

The OS is a more technically complete and elegant solution. The engine oil is separated out of the crankcase fumes, and returns to the sump, instead of being sent into the combustion chamber. It comes with a downside, which is that it is harder to maintain than a PCV valve (which we used to just throw away and replace).

I see. That's the point I was missing. My M42 engine had a gummy throttle body and intake manifold because of the simpler system.

Why can't the oil separator valve just be removed all together? I would like to remove it and just plug up the passage to the intake and vent the crankcase pressure to atmosphere.

Any issues that will come up if I do that?

If you hang the tube down into the airstream underneath the vehicle, you will have created a road draft tube, whereby the vacuum created by the passing air draws out the crankcase fumes, and drops oil onto the road. That was the approach used from 1930 until 1960 or so, when PCVs were invented.

In the same vein, if you went back to solid tires you would never get a flat, and if you went back to a distributor you wouldn't ever have a failure of a coil pack.

Seriously, don't do it, it is completely irresponsible.

It is hard to see when faced with a failure of an OS or CCV, but we really have it very good. We don't have to worry about rings and pistons, about valve grinds or valve stem seals. We don't have to replace points, condensors, distributor caps, rotors, vacuum advances, or HT leads. We safely go ridiculously long intervals on scheduled maintenance (remember when it was a good idea to do oil changes every 3000 miles?). We don't replace worn shock absorbers, or brake linings, or exhaust systems every year or so. Water pumps used to be a semi-annual event. Because the rest of the vehicle has become so maintenance free, all we have to talk about is a crankcase ventilation valve (and an occasional vanos system, but for the sake of the example...). So really, a slightly troublesome CCV, which is only a problem for vehicles that don't get hot enough to burn off the condensation, is really a non-issue IMO. These are the best days ever to not have to spend money fixing a car.

/end rant.

Bawahahahahahaha!!!! Well said and good point! It's funny because that comment is very "my sence of humor". But I hear ya. I also wanted to be sure I understood the system correctly. Some times I question if my motor is a little sluggish off the bottom, and because I gave up on the third hose... I wondered if I was sucking in unaccounted for air if the third hose was as badly decomposed as the first two.

And no I don't think it would have thrown a error code. When my tranny shit the bed 1.5 months ago, it acted like a spoiled brat throwing a tantrum FOR A PERIOD OF TIME before I got "limp mode". So this is why I want to ax that separator system.... Tempararly for diag porposes.