Inside the nipple is a restrictor...a small orifice...that reduces the flow through the nipple.

From the outside, the nipple looks like it can flow decently: it is about 1/2in in diameter; so it should flow good.

But, when you look inside and see that tiny orifice...about 1/3 the size of the nipple itself...it becomes quite obvious that there is NOT going to be a lot of flow through there.

Why Volvo decided to put that tiny orifice in there: dunno and don't care. It may be just fine for an NA PCV setup. But a boosted motor will have more blowby under boost, and that blowby has to be allowed to get out of the crankcase.

I could have drilled out the small orifice to improve the flow. But I wanted to go further than that; and set things up so that as the miles add up, or if the boost levels go higher, then the PCV setup will be able to handle the flow. Eliminating the nipple became part of the plan.

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SIDENOTE: Drilling out the orifice is a viable modification for someone who has a slight seepage/wetness problem. Drilling out the restriction would definitely improve the flow, thereby reducing the crankcase pressure. Eliminating the nipple is another means of improving the flow, without going for the dual-hose-setup-feeding-into-a-catch-can such as being shown here.

In other words: drilling out the restriction in the nipple can be viewed as a staged level of modification. Easily done; and if the results are sufficient for the motor, then that may be as far as needed to go. If improvements result, but not a total correction, then going further and doing a dual hose mod to the separator and installing a catch can would be the next stage...and resolve the issue once and for all.

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IF, when doing the auxiliary vent setup the first time around, I had actually removed the nipple from on top of the separator, and looked inside, I would have seen that tiny orifice and realized then what that restrictor would do.

But, I did not do that then. And I created a problem for myself.

The one good thing about my NOT finding that restrictor orifice in the nipple at that time is this: I came up with a better way to improve the crankcase venting system...the catch can setup that is being shown in this gallery. Still, trying to explain 'why' something that I did that was supposed to take care of things, but which ended up creating a new problem, was NOT my idea of fun. It did help that the Streak's owner is a reasonably patient and understanding person. He trusted that I would figure it out; which I finally did do. The catch can setup has been on for a few months; and is working even better than I had hoped.

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As to the "why" and "how" the restricted flow through the nipple caused an onset of oil consumption:

When I installed the second hose from the cam cover over to the intake pipe, it actually became the main vent hose: because it did not have a restrictor orifice. The crankcase vapors had an easier path to the intake pipe, and they took it.

Well, inside the cam cover, there is some oil splashin' going on due to the cam lobes rotating and making the tappets go up and down...all that going on with the tappets being semi-submerged in oil. And since the Streak is running with an Acam, the splashing is a bit more than what a Tcam generates.

However, the main thing was that the cam cover vent was having to accomodate most of the crankcase vapor flow, rather than just sharing the flow with the primary hose coming up from the separator. Increased flow rate through a hose causes a velocity increase of the flowing vapors. Combine the velocity of the vapor flow with the fact that there is no 'separator' under the elbow in the cam cover to permit precipitation of oil out of the vapors, and that meant that oil drops as well as oil laden vapors were going to be going through that secondary hose, and into the engine.

THAT is why and how I ended up with an oil consumption problem where it had not been a problem priorly.

On the first motor that I had done the auxiliary vent hose mod to, I had eliminated the nipple. And that was why I had not had an oil consumption problem on that motor: the flow through the two vent hoses to the intake pipe were even...and slow.