N52 oil separator delete question

Grossbauer · 02-11-2018, 09:14 AM

I have deleted my oil separator on my 2007 E60 525xi with N52 that has the magnesium valve cover. I am under the impression that the oil sep has the PVC valve built in. Can someone explain the function of the valve? For now I have vented the output hose from the back of the valve cover to the atmosphere but I am getting strong oily smell from it. I also capped off the oil return line to the crankcase and capped off the vent lines at the manifold. I plan on adding an oil catch can but need to know if I need to return the remaining vapors to the manifold and if I need to add a check valve or some sort of PCV valve or can it go straight through. I have run it the way it is for a week and no CE lights. Thanks.

Odis-Elsa · 05-26-2025, 04:38 AM

Hi Grossbauer,

I saw your post about removing the oil separator on your 2007 525xi with the N52 and magnesium valve cover. I’m in the middle of a 3-stage intake manifold swap on my 2006 E61 525xi (N52B25A), and I’m trying to figure out how to deal with the PCV system now that the manifold I installed has the integrated oil separator.

My original setup had the external oil reservoir/separator (the black plastic dome under the manifold), but with the new 3-stage manifold (from an N52B30), that piece isn’t there anymore — and I’m not sure if I’m supposed to reuse it or just delete it completely.

So my main question is:
Do I need to reuse the old external oil reservoir somehow with the new manifold, or is it fully replaced by the integrated separator in the manifold?

I’m not sure what to do with the hoses that originally connected to it (from the valve cover and oil return). Any guidance on whether I can just run those differently now, or if I need to connect them to something else?

Appreciate any help or insight you might have!

Best regards,
ODIS-ELSA-OLSEN
(E61 525xi N52B25A – Trondheim, Norway)

aade · 07-16-2025, 06:32 AM

The PCV is very important to the ventilation of the crank case and you really don't want that oil that comes out of the valve cover to spray all over your engine bay. In addition it'll allow unmetered air into the combustion chamber and you'll end up with rough running.

The N52B25A with the magnesium valve cover has the PCV separate from the valve cover. The plastic valve cover version has the PCV built in to the valve cover. Both of you need to have a proper functioning PCV. @Odis-Elsa if your intake didn't come with a PCV, you'll need to get one. If the one you already have on your original manifold is in good working order, reinstall that one. Otherwise buy a new one. If you want after market, I'd recommend Febi Bilstein. If you've installed an intake manifold that doesn't have a mounting bracket for the external PCV, you'll have to get one.

And one other question @Odis-Elsa, the 525i already comes with a three stage intake manifold. Why would you swap that for a new one? The 523i has one DISA valve, so technically that's a 2 stage intake manifold, but for sure the 525i has two. Or did you do the manifold swap with some sort of after market version made for the plastic valve cover N52?

02-11-2018, 09:14 AM	#1
Grossbauer Registered 0 Rep 1 Posts Drives: 2007 525xi Join Date: Feb 2018 Location: United States iTrader: (0)	N52 oil separator delete question I have deleted my oil separator on my 2007 E60 525xi with N52 that has the magnesium valve cover. I am under the impression that the oil sep has the PVC valve built in. Can someone explain the function of the valve? For now I have vented the output hose from the back of the valve cover to the atmosphere but I am getting strong oily smell from it. I also capped off the oil return line to the crankcase and capped off the vent lines at the manifold. I plan on adding an oil catch can but need to know if I need to return the remaining vapors to the manifold and if I need to add a check valve or some sort of PCV valve or can it go straight through. I have run it the way it is for a week and no CE lights. Thanks.
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05-26-2025, 04:38 AM	#2
Odis-Elsa Registered 0 Rep 2 Posts Drives: BMW 525IXA Join Date: May 2025 Location: Norway iTrader: (0)	Hi Grossbauer, I saw your post about removing the oil separator on your 2007 525xi with the N52 and magnesium valve cover. I’m in the middle of a 3-stage intake manifold swap on my 2006 E61 525xi (N52B25A), and I’m trying to figure out how to deal with the PCV system now that the manifold I installed has the integrated oil separator. My original setup had the external oil reservoir/separator (the black plastic dome under the manifold), but with the new 3-stage manifold (from an N52B30), that piece isn’t there anymore — and I’m not sure if I’m supposed to reuse it or just delete it completely. So my main question is: Do I need to reuse the old external oil reservoir somehow with the new manifold, or is it fully replaced by the integrated separator in the manifold? I’m not sure what to do with the hoses that originally connected to it (from the valve cover and oil return). Any guidance on whether I can just run those differently now, or if I need to connect them to something else? Appreciate any help or insight you might have! Best regards, ODIS-ELSA-OLSEN (E61 525xi N52B25A – Trondheim, Norway)
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07-16-2025, 06:32 AM	#3
aade New Member 5 Rep 82 Posts Drives: BMW E61 5er Join Date: Jul 2025 Location: Stockholm iTrader: (0)	The PCV is very important to the ventilation of the crank case and you really don't want that oil that comes out of the valve cover to spray all over your engine bay. In addition it'll allow unmetered air into the combustion chamber and you'll end up with rough running. The N52B25A with the magnesium valve cover has the PCV separate from the valve cover. The plastic valve cover version has the PCV built in to the valve cover. Both of you need to have a proper functioning PCV. @Odis-Elsa if your intake didn't come with a PCV, you'll need to get one. If the one you already have on your original manifold is in good working order, reinstall that one. Otherwise buy a new one. If you want after market, I'd recommend Febi Bilstein. If you've installed an intake manifold that doesn't have a mounting bracket for the external PCV, you'll have to get one. And one other question @Odis-Elsa, the 525i already comes with a three stage intake manifold. Why would you swap that for a new one? The 523i has one DISA valve, so technically that's a 2 stage intake manifold, but for sure the 525i has two. Or did you do the manifold swap with some sort of after market version made for the plastic valve cover N52?
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