HappyAndy UltraDork
5/26/14 7:10 p.m.

The Bimmer in question is a '95 E34 525iA. I've been chasing a stubborn oil leak from the valve cover gasket , but my question isn't really about that, at least not directly.

My question is about the m50's PCV system, or apparent lack of said PCV system.

I see the crank case ventilation system connector on the valve cover with a large hose connecting to the intake duct, and the smaller vacuum hose that connects to the same fitting on the valve cover then goes to somewhere on the intake manifold.

Am I correct that the little vacuum hose is all that supplies vacuum to the crank case? Is there no traditional PCV check valve any where in the system? It seems odd to me to have the fresh air supply and vacuum source right on top of each other.

The system seems to be sealed and working, when I remove the oil cap the idle speed dips down a bit, and goes back to normal when I put it back on, but it doesn't have enough vacuum to keep the cap from bouncing around if its not twisted into place.

I'm also wondering if the lack of crank case vacuum is contributing to the oil leak, I've seen that on some other engines.

02Pilot HalfDork
5/26/14 8:53 p.m.

I don't know much about the M50 system, but from what I can see it's a simplified version of the later M54, with which I am very familiar.

I found that low crankcase vacuum was problematic on the M54. The spec is very low. If you happen to have a slack tube manometer, you can measure the vacuum, but even if it's in spec I wouldn't be surprised if it's contributing to your leak.

My solution was to introduce considerably more vacuum into the crankcase under closed-throttle condition - this solved my oil consumption problem. All the details (and I do mean all) are here: http://forums.bimmerforums.com/forum/showthread.php?1629018-Oil-consumption-after-CCV-replacement

spandak New Reader
5/27/14 2:24 a.m.

Im no M50 expert but Ive owned and worked on two of them. The only hoses are those two. The small one fits onto the same same connector as the idle air control. The large hose fits into the elbow before the TB. Where is your valve cover leak? Mine have always seeped a little at the oil fill cap and at that connector for those hoses at the valve cover. Ive replaced the O ring in the connector but it didnt seem to do much. I tend to be pretty liberal with silicone sealer when installing the valve cover gasket and I have never had any major leaks.

HappyAndy UltraDork
5/27/14 6:32 a.m.

In reply to 02Pilot: That's quite a tale! I read the whole thread before bed last night, and wound up dreaming about manometers.

It made me wonder why the extra vacuum fitting is on the CCV in the first place? Maybe someone knew that it needed more vacuum?

Vacuum in the crank case is good,(within reason ), in fact some racing engine builders add external vacuum pumps to keep negative pressure at all times for more power and better ring seating, not just for emissions. There is generally no down side to a reasonable amount of crank case vacuum, and real harm from lack of it. It makes me wonder why BMW would have such a lame CCV system.

I devise a catch can if the problem persists.

HappyAndy UltraDork
5/27/14 6:46 a.m.

In reply to spandak:

Before I replaced the VCG it leaked in the front and dripped oil onto the chain tensioner and AC compressor.

With the new VCG , and clean out of the breather baffle under the Valve cover it then had a drip of oil onto the exhaust manifold, and seems to have a film of oil everywhere under the top cover.

I also suspect that my valve cover has a porous spot in the casting right over the vanos mechanism, because it always has a small oily spot there. IMO, if it had proper crank case vacuum minor porousness wouldn't be an issue.

Yesterday I pulled the valve cover off, super cleaned the mating surfaces, and put the gasket back with much more use of sealant than the first time. I also made sure that the valve cover stayed perfectly centered while tightening it down this time, I was in a bit of a rush the first time.

02Pilot HalfDork
5/27/14 7:04 a.m.

Supposedly (this is purely hearsay) the extra vacuum fitting on the CCV supplied vacuum to the fuel pressure regulator in very early M54s. They soon moved the FPR and did away with the need for vacuum. It was never intended for supplying crankcase vacuum.

iceracer PowerDork
5/27/14 8:59 a.m.

You also need a source of fresh air to create circulation.

Air in, fumes out.

02Pilot HalfDork
5/27/14 12:03 p.m.
iceracer wrote: You also need a source of fresh air to create circulation. Air in, fumes out.

The BMW system doesn't have a fresh air intake, nor do many modern systems (for emissions reasons). These systems maintain a low vacuum in the crankcase, which would of course be impossible with a fresh air vent.

spandak New Reader
5/27/14 12:34 p.m.

Those sound like the usual trouble spots. Its recommended to put some sealant on the seam between the vanos and the head. I know another problem spot is the cut outs at the back of the head for the cams. Ive never had any leaking above the exhaust manifold so I cant help you there. One of the motors I worked on had a stripped stud on that side so it seeped a little but it was never too bad. Small detail but make sure you are using the high temp sealant too. I did two VCGs and used the regular stuff and it seeped both times. This last time I used high temp and last I checked everything is still dry. Ive been pretty blessed so far, 210k on an unopened motor and I use less than a quart between changes.

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