Crankcase ventilation mystery / People think my car is on fire :-)

[tgrandahl]

So I have had an issue of burning oil while driving my car for awhile. It started last spring when I took the car out from storage. I had replaced the valve cover gasket because I had oil leaking into the plug wells.

Oil has been leaking off the head and onto the headers where it burns and leaves a nice black smoke trail.

My uncle suggested that it was a crankcase ventilation issue most likley and not the new gasket. I tried driving around for awhile with the oil fill cap turned loose and a rag over it to keep the cap from falling off. The burning oil stops.....

So today I check through all the hoses for blocks and to my disappointment I find nothing... Its all totally clear.

Part 4 does not exist, I just have 1 and 3, the hose connects to part 16 in the next picture.

http://www.realoem.com/bmw/diagrams/c/n/7.png

http://www.realoem.com/bmw/diagrams/k/t/22.png

The other hose from part 16 runs into one of the lower hose barbs in the throttle body.

http://www.realoem.com/bmw/diagrams/h/d/5.png

These parts are all clear and I can blow and suck air from the intake through the hose going to the throttle body.

When I remove the oil fill cap from the valve cover I can blow and suck air through the hose feeding into the valve cover (parts 1 and 3).

The disturbing part is that when I run and rev the engine with my finger over the hose from the valve cover I don't feel pressure building as I expected. There is a vacuum present that increases with rpm... When I feel the hose going to throttle body I expected to find a vacuum, only to find no vacuum nor pressure. The passage is not blocked I can still suck air out of it, and I can blow air into it and start to stall the engine.

Honestly, why couldn't there just be some oily mess clogging one of the hoses that I could clean out. Would that really be to easy?

So my questions are.....
-why is having a vacuum pushing oil out past the valve cover seals?
-why does the totally unblocked ventilation system not prevent this but loosening the fill cap does?
-where is vacuum coming from, intake valves not seating?

on a second note I just made it over 200,000 Mi ! so i suppose a valve job could be in order but the oil and ventilation just confuses me.

I also just ran a compression test and every cylinder scored A+ ~250psi all round!

Any ideas guys?

Thanks,
Tyler

[Ross]

The vacuum at the hose is normal and is from the engine's aspiration.
Opening the cap relieves crankcase pressure same as a functioning PCV should.
I believe there is a baffle in the rocker cover to prevent oil spray from entering the PCV system, perhaps this is clogged pressurizing the crankcase and blowing oil past the seal. Check for pressure at the port on the cover for the hose with the cap closed, it may only be slight. Compare with the opening for the filler cap. If you have more pressure builing at the filler cap I'd look into a restricted baffle.

[tgrandahl]

The vacuum at the hose is normal and is from the engine's aspiration.
This is what i was expecting, I was under the impression that the only source of vacuum in an engine was from the venturi effect in the intake?


I believe there is a baffle in the rocker cover to prevent oil spray from entering the PCV system, perhaps this is clogged pressurizing the crankcase and blowing oil past the seal.

I remember this baffle from when I replaced the valve cover gasket.

The pressure / vacuum at the port where part 1 in the first photo fits is the same pressure / vacuum as I find at the opening for the the fill cap.

However even if the baffle over the intake cam was covered with tons of crap I still have a vacuum, negative pressure, at the fill cap port. This does not make any sense to me because I have the line from the throttle body where the vacuum should be coming from, disconnected from the engine.

So unless there are some other PCV lines that I am not aware of, the vacuum is coming from inside the engine somewhere, right?

~Tyler

[Ross]

I don't have an M50 in front of me look at so only have the parts diagram you provided.
You are saying that with the vacuum hose that generally evacuates the crankcase disconnected there is still suction at the oil filler. ?!
I don't see any other source but there must be one. Bad piston rings would create positive pressure, blowby combustion gases, that the PCV is there to take in and burn.
I can't conceive any way that the crankcase would have negative pressure other than manifold vacuum being introduced.
Inded if you do have neg. crankcase pressure the PCV would seem to be functioning.
Whatever the PCV is doing it still looks like a failed gasket is allowing the dripping. I suspect all this vacuum business we are chasing is a
red herring and the real issue is simply the gasket.
While driving your negative crankcase pressure could very well be the opposite explaining the oil loss through a failed seal/gasket, whatever.

[Ferret]

One thing to check, that I fell foul of - make sure your camshaft sensor is done up tightly, and that the rubber o-ring isnt cracked! Mine used to stream oil past this and would cause a smoke screen!

[genphreak]

if oil is coming out, air is going in...
Other hose is the FPR host at the back, its hard to check adn it cracks up. Normally causes fuel pressure problems however so you would be seeing bad running under throttle and perhaps otherwise also...

[Tiger]

Majority of the crankcase ventilation problem is the PCV unit itself... they do go bad after a decade of service... so if it has never been changed, it is time to do so.

[whiskychaser]

Hoses on mine are:
Small hose 3 in diag 1 goes to stub on 9 in diag 2
Hose 5 goes to bottom of large hose between throttle body and MAF.
(There is also a seperate inlet there for the hose from the ICV)
I dont have part 4 either.

I remember doing a test to ensure there were no vacuum leaks on mine - you tape a plastic bag over the mouth of the oil filler hole and see if it gets sucked in. It does. If you put your thumb over the end of hose 3 on mine, there is a small vacuum. There should be as its upsteam of the inlet manifold. If you put your thumb over the end of part 1 for a few seconds, you get a small hiss of air.

Mine doesnt burn oil but I do get a tiny bit inside the throttle body. Appreciate you have a new gasket but could the bolts be bottoming before tightening down the valve cover?

[tgrandahl]

Mine doesn't burn oil but I do get a tiny bit inside the throttle body. Appreciate you have a new gasket but could the bolts be bottoming before tightening down the valve cover?

Good question, I tightened them to the torque and pattern specified in the Bentley. I also used a new gasket from pelican parts so i assume it is the correct thickness. Im not sure how i could check this except try to tighten them some more (break them).

I think i am going to take the cover off this weekend and inspect. The leak is on the back by the two rubber fillers that plug the half moons in back of the cams. Does anyone have any tricks to applying the gaskets? Im thinking HEAD + RTV + Gasket + RTV + Valve cover.

On another note has anyone ever had trouble with warping valve covers? When I originally took the cover off the sealing surface looked like ****.
http://farm4.static.flickr.com/3007/2702443038_355094bc64.jpg?v=0

So i cleaned it but was not able to do so on a mill. I may try to this weekend or at least tram it.
http://farm4.static.flickr.com/3234/2702441344_9c799c22b6.jpg?v=0

~Tyler

[whiskychaser]

The bolt doesnt need to be really tight. But there is a steel washer and a rubber washer under it. Imagine if the rubber washer was half normal thickness. Or in my case - and I know I am not the first - you end up with a washer short somewhere. Result is you dont get even pressure on the cover and it leaks. Pretty much what Ross was getting at. Wonder how he knows?;)

[genphreak]

Make sure your sealant is catalytic converter safe type ****.

It has to say it on the tube :) else it is not.

[tgrandahl]

Make sure your sealant is catalytic converter safe type ****.

It has to say it on the tube :) else it is not.

You mean the RTV? How will it be getting into my cat?

[Tiger]

Awesome photo... one of a kind.

[Ross]

You mean the RTV? How will it be getting into my cat?

It won't, don't worry.