M70 Oil In Intake Manifold

[Albert850i]

I tested 4 VCV valves and they all operated identically: fully open when blowing hard, and slightly restricted when blowing really really hard. So apart from full throttle / high rev conditions, these valves appear to be just open. So I guess they allow the intake manifolds to suck in unmetered air from the interconnected valve covers, leaning the mixture. What am I missing?

[m6bigdog]

I tested 4 VCV valves and they all operated identically: fully open when blowing hard, and slightly restricted when blowing really really hard. So apart from full throttle / high rev conditions, these valves appear to be just open. So I guess they allow the intake manifolds to suck in unmetered air from the interconnected valve covers, leaning the mixture. What am I missing?

Yes, you are missing something.
The crankcase is designed as a sealed volume and once the intake manifold/PVC regular negative pressure is balanced with the crankcase the crankcase venting will be limited to the flow necessary that maintains the designed negative pressure.
The only normal leakage into the crankcase is a small amount of piston ring blow-by.
A bad engine may have excessive leakage into the crankcase from worn piston rings, other seals and gaskets that should be repaired to return the crankcase to an appropriately sealed volume.

[Albert850i]

Shouldn’t a PCV valve be closed during idling (suction) and with engine off?

[m6bigdog]

Shouldn’t a PCV valve be closed during idling (suction) and with engine off?

Why,
There should very little air flowing threw the PCV into the intake at any time and when the engine is off there is none.
The PCV's main function besides providing a path for crankcase fumes into the intake manifold is to be a "check-valve" for when the engine backfires in the intake manifold to prevent the flame and pressure from entering the crankcase; as the oil mist in the crankcase is combustible.

[Albert850i]

Thanks for the info. Based on this, I declare my 2 original and 2 relatively new PCV valves as defective. I will replace them obviously, however, not with the BMW parts anymore as these do not appear reliable.

[m6bigdog]

Thanks for the info. Based on this, I declare my 2 original and 2 relatively new PCV valves as defective. I will replace them obviously, however, not with the BMW parts anymore as these do not appear reliable.

Why do you consider them defective?
I believe you are misunderstanding some of my explanations...

The typical diagnosis for the barrel type PCV is to shake it and if it rattles then the valve is considered functional.
https://www.youtube.com/watch?v=HlkvIegt848

These are simple seat, sliding plunger and spring devices.

fully open when blowing hard, and slightly restricted when blowing really really hard

Your description seems typical however if you are blowing by mouth that is a poor source of pressure.

I suggest you test the PCV by replacing the oil filler cap with a test cap with vacuum gauge attached.

Also,
https://www.aa1car.com/library/pcv.htm

[Albert850i]

Thanks.
Shaking test: no sound as no metallic parts inside.
With engine off, the valve should close by spring, which is not the case (actually fully open).
Blowing or sucking by mouth is not very scientific indeed, but indicative (to me).
As M20B25 engines have no PCV valve at all (ventilation hose connected just upstream of throttle), I think I'll reroute the outlet of my PCV/VCV's to the inlet at the rubber boot between MAF and throttle body. Less fancy pressure control, but less unmetered air entering the inlet manifold effecting the mixture. Or use a completely different PCV.
Screenshot 2022-08-11 at 11.37.55.jpgScreenshot 2022-08-11 at 11.52.34.jpg

[shogun]

There is no need to change to another system. The system is quite reliable since they modified the valves many years ago. Difference old/new is mentioned here = white plunger = new type http://bmwe32.masscom.net/sean750/vc.../VCVvalves.htm
In 30 years I own my 750 I had only to replace these parts once, when I noticed oil consumption. I replaced:
11151720392 vacuum hose left 1
11151720393 vacuum hose right 1
11151720131 non return valve 2
11151718642 2 stage valve left 1
11151718713 2 stage valve right 1

Before replacing the parts I made my own oil catch system for a temporary test like this http://twrite.org/shogunnew/upgrades...or_Shoguns_M70


On page 1 of this thread there is the BMW Service Information SI B11 03 13 technical service, excerpt:
Crankcase Ventilation
The crankcase ventilation systems use various different crankcase ventilation valves, depending on the engine type. Although the valves all look different, they function similarly, using a spring and diaphragm assembly to control the crankcase pressure. A properly functioning pressure control valve is designed to maintain a slight vacuum (under-pressure) in the crankcase, which assures reliable crankcase venting during all engine operating conditions. One of the results of a malfunctioning crankcase ventilation system can be increased engine oil consumption. Refer to SI B11 03 08 for measuring specifications and procedures.

[shogun]

This Service Information bulletin supersedes SI B11 03 08 dated August 2011. designates changes to this revision
SUBJECT Crankcase Ventilation System Diagnosis and Measurement
MODEL All
INFORMATION: All current BMW engines incorporate a pressure-controlled crankcase ventilation system. The crankcase ventilation systems use various different crankcase ventilation valves, depending on the engine type. Although the valves all look different, they function similarly, using a spring and diaphragm assembly to control the crankcase pressure. A properly functioning pressure control valve is designed to maintain a slight vacuum (underpressure) in the crankcase, which assures reliable crankcase venting during all engine operating conditions. Some of the causes and results of a malfunctioning crankcase ventilation system are listed below.

Causes of Excessive Overpressure (Pressure)
 Internal engine damage/wear
 Obstruction in the crankcase ventilation system
 Defective pressure control valve(s)

Results of Excessive Overpressure
 Damage to the engine oil seals
 Increased engine oil consumption (can be misdiagnosed as a defective turbocharger)
 Excessive engine oil in the intake system
 Excessive engine oil in the charged intake tubes or the intercooler on turbocharged engines (can be misdiagnosed as a defective turbocharger)
 Engine oil dip stick is dislodged from the guide tube (if equipped)

Cause of Excessive Underpressure (Vacuum)
 Defective pressure control valve

Results of Excessive Underpressure
 Damage to the engine oil seals
 Increased engine oil consumption
 Excessive engine oil in the intake system
 Rough engine idling or engine misfire
 Whistling or howling noise from the engine (can be misdiagnosed as a defective turbocharger)
 Increased mixture adaptation values

Attached to this Service Information bulletin is a procedure for measuring the crankcase ventilation system, using the ISID and IMIB diagnostic equipment. Specification and actual readings from the vehicle may vary by up to ±10%, but not more than 5.0 mBar. Various measuring tools may provide results that are not within specification. All measurements below were recorded using the IMIB. See the attachment for IMIB connection hints.

Engine Variant........................................... ................................................ Specification (mBar)
M42, M44, M52, M52TU, S52 ,M54, M60, M62, M62TU, M73............................ 16.0
M57Y.............................................. .................................................. ......... 0.0 +- 1.0
S54............................................... .................................................. .......... 0.0 +- 1.0
S62 .................................................. .................................................. .......0.0 +- 1.0
S65............................................... .................................................. .......... 0.0 +- 2.0
S63............................................... .................................................. .......... 25.0
S63T.............................................. .................................................. .......... 45.0 – 50.0
S85............................................... .................................................. ........... 0.0 +- 1.0
N20 and N26............................................... .................................................3 5.0
N52............................................... .................................................. ............30.0
N51 and N52K.............................................. ................................................ 33.0
N52T.............................................. .................................................. .............21.0
N54............................................... .................................................. ............ 17.0
N54T.............................................. .................................................. ............ 14.0
N55............................................... .................................................. .............50.0 +/- 8.0
N62............................................... .................................................. .............22.0
N62TU............................................. .................................................. ...........40.0
N63............................................... .................................................. ............15.0
N63T.............................................. .................................................. ........... 45.0 – 50.0
N73............................................... .................................................. ............30.0
N74............................................... .................................................. ............17.0

https://static.nhtsa.gov/odi/tsbs/20...50094-9999.pdf

[Albert850i]

Thanks, interesting. Not sure how to diagnose our M70 ventilation system though, as we have 2 PCV/VCV's but just one common crank case. Perhaps disconnect one PCV and measure the pressure at the dipstick opening. Then repeat with the PCV on the other bank disconnected. Also no vacuum level specified for old engines like M70 (16 mBar or 32 mBar?). Perhaps I'll do this test, and report back.

Can you confirm that our PCV/VCV's are closed with engine off, and almost closed (in the other direction) due to idling vacuum? Not what I'm observing.

[shogun]

I do not have data for the M70 engine. There is also nothing in the E31 workshop manual about this in detail. Here in this thread some tips are mentioned http://bmwe32.masscom.net/sean750/vc.../VCVvalves.htm
Guy Simpson about this:
"A little theory on the PCV system as I think it works. The actual valve on the valve cover is a two-stage valve. If you blow through it in the proper direction, very tasty BTW, a low air flow will go through easily (1st stage), whereas a high flow air pulse (blow real hard) will cause the valve to shift to a low flow condition (2nd stage). The high vacuum of the intake should cause the valve to go to stage 2 as a normal condition and allowing a restricted flow from the crank to the intake. If it didn't I could see a situation where the intakes would draw too much oil vapor and again high oil usage. There is an additional input to this valve coming from a check valve located in the boot between the MAF sensor and DK throttle motor. And in all normal circumstances this check valve is closed and not allowing any flow toward the PCV valve. It's my bet that BMW built in a safety feature so if for some reason the PCV valve malfunctioned and remained in stage one, then the check valve would open and allow fresh air into the intake via the malfunctioning PCV valve. If this safety circuit were non existent you would be losing a lot of oil going into the intake and your MAF reading would be off since now the crank is providing some amount of air instead of being drawn in by the normal pathways. With a bad valve your MAF reading is still good as the check valve is down wind."

Brett Anderson about this:
"I noticed on mine that after a period of deaccelerating (no smoke), putting your foot on the gas made smoke. When 'coasting', the fuel is entirely cut off to the injectors, the inlet vacuum is maximum which sucks the oil in."

Guy Simpson about this:
"I was using about 1 quart every 400 miles. There were absolutely no indications there was a problem. I found a symptom by wanting to add oil while engine running and noticed a hissing noise emitted from the oil fill cap upon removal. Using my hand next determined this was pressure and not vacuum."

This is an important check. Check the oil fill cap for vacuum, for instance by using a small thin plastic bag across the opening. Don't let it get sucked into the engine, as your weekend will probably ruined. If you don't have any crankcase vacuum but pressure instead, this could be related to faulty VCV valves.

Patrick C about this: "You can do a quick test on the state of crankcase vacuum by removing the oil filler cap and stretch by two hands a plastic supermarket bag across the opening. The membrane should be seem pulled into the crankcase (but don't let go the bag!) if there is vacuum inside."

Background: the term 'PCV' valve is not appropriate. PCV is positive crankcase ventilation valve. The v12 has a negative crankcase pressure. So these are VCV valves (volume control valves). The high intake vacuum sucks the oil-contaminated fumes (mist) from the crankcase right into the manifolds so they get burned in the combustion process. When the vacuum is to high, or in other words: when there is a risk that engine oil could be sucked into the manifolds, clean filtered air enters the manifolds by using the bypass hose and the non return valve, attached to the intake boot. One remark must be made: even with a properly functioning VCV system and/or valve stem seals, the intake manifolds always tend to be a bit oily from the inside. This is due to the system of negative crankcase pressure and therefore absolutely normal.

How to recognize a new modified type and an old type of VCV valve? Look into the valve from the back. If you see a white plunger, it's the new type. If you see a black plunger, it's the old type.
Old type: http://bmwe32.masscom.net/sean750/vc...PlungerVCV.jpg
New type http://bmwe32.masscom.net/sean750/vc...PlungerVCV.jpg

My own quick and dirty test on the state of crankcase vacuum is by removing the oil filler cap and stretch by two hands a plastic supermarket bag across the opening. The membrane should be seem pulled into the crankcase (but don't let go the bag!) if there is vacuum inside."

Here Patrick made a home made oil separator to test the oil consumption http://www.bimmerboard.com/forums/posts/167777/

in 2010 I posted: How you check PCV system on a 750 V12 https://www.bimmerforums.com/forum/s...m-on-a-750-V12

[Timm]

The way to test if the PCV is working (Pressure Control Valve) is to measure the crankcase vacuum at the dipstick tube with a manometer - either an electronic one or a length of tube as shown below:





The PCV valves have the same function across the E31, they are just physically different between the V8 and the V12 - they maintain a fixed crankcase vacuum in all conditions as set by the spring and the bullet end on the V12.

A bit more detail on the crankcase ventilation system here: https://www.meeknet.co.uk/e31/BMW_M6...entilation.htm

[Albert850i]

Shogun, I read that site many times, but there is no clear explanation on how the VCV system is designed to work. Connecting anything to the inlet manifold will see negative pressures, clear.
Timm, the M70 valve has no "bullet inside", see picture I just made. It is permanently open, but closes slightly at high flows. So very different from traditional PCV valves.
The hose from the inlet boot allows free flow of (metered) air to bypass the throttle body, directly into the inlet manifold. Not sure why this is allowed, considering the accurately adjusted throttle plate.
But the problem is that the (unmetered) crankcase gasses entering the engine do affect the mixture.
IMG_3176.jpg

[Timm]

As m6bigdog says - the crankcase isn't a source of air, it's a sealed container with only blow-by gasses at a very low level reaching the manifold. And the PCV, in whatever form it is, has the same function - to maintain a negative pressure in the crankcase - and that can be measured at the dipstick tube.

[m6bigdog]

Look what I found in my library of paper SIB documents.
I first scanned it into a PDF but that was too large to post here as a single 3-page document.

Attached is the BMW SI B11 01 90 Crankcase Vent System M70.
Explanation of system and individual components.
The M70 Crankcase Vent System is much more complex than I realized (relying on 2 valves on each bank to function properly), however this document although dated is the best I've seen.
No wonder BMW developed the diaphragm style vent system used on the later model engines; like the M73

[Albert850i]

Thanks, best info ever.
It seems that the "MBV" valves operate similar to regular PCV valves. The additional "RSV" valve will limit the vacuum level, letting air into the inlet manifold past the throttle body (I still don't understand how that wouldn't affect idle). I tried but cannot get my valves to close, so there appears to be an open connection between valve cover and inlet manifold, causing mixture and blue smoke issues on my car.
BTW I measured vacuum levels at the dipstick and at the oil filler cap, but no movement of my gauge needle. A piece of paper sticks though, so there must be some negative pressure.
The SI starts by saying that the M70 system is similar to the 6-cylinder ventilation system, but on my M20B25, there is no PCV valve at all and the valve cover ventilates just before the throttle body. With a bit of vacuum due to the resistance of the air filter.; simple but effective. Probably another example of over-engineering on our M70's..

[Albert850i]

IMG_3194.jpg
By the way, using an accurate digital gauge, I just measured -4 mBar dipstick / filler cap pressure, way too high (should be around -15 mBar).

[Albert850i]

BMW M20 engines have a completely sealed crank case, so there is no real ventilation and no PCV. Just a hose between valve cover and throttle body.
Is that also the case for M70 engines? In case of true ventilation (which most engines appear to have), there should also be a clean air inlet to the crank case right? Not on the M70?

[Timm]

Since the 1980's it is unlawful to have a fresh-air OUTLET - that went with the bit-of-foam-in-the-filler-cap days! The hose between the crankcase and throttle body causes a vacuum in the crankcase (the hose connects to the vacuum side of the throttle) - but that caused high negative pressure on the over-run which could pull oil from the crankcase or, in the worst case, pull seals.

Since the 1980's BMW have put a Pressure Control Valve between the vacuum point and the crankcase to stop this happening, there's always a PCV somewhere including the M70.

[E36Ron]

This is a very intriguing thread. But it still leaves some open questions.

On the positive side, I conclude that some oil in the intake manifolds is "normal," and acceptable -- and not an indication of a source of excessive oil consumption.

But, so far, the cause of Albert850i's oil consumption is not identified. Even though he apparently detects negative pressure at the oil filler cap (or the dipstick).

So that leaves the question: with replaced valve seals, and no evidence of oil bypassing the piston rings, or any noticeable blackening of the spark plugs upon inspection, is it possible to pass this "negative pressure" test, and yet still have some defect in either or both VCV setups cause excessive oil consumption?

After all, what else is left???

Should he just throw two new sets of VCV valves at it?

I am extremely interested in this because I have the same problem, but I'm paying someone by the hour to try to solve it.

-- E36Ron

[Albert850i]

I modified the crankcase ventilation hose routing.
See image: left hand side original, right hand side modified.
Hoses now run between valve covers and the air boxes just below the filters.
No more smoking..
75A66B9C-3B9A-406F-BA7C-701AEE792D8E_1_201_a.jpg

[cartoonz]

Congrats, you figured out how to destroy your MAF's

[m6bigdog]

I modified the crankcase ventilation hose routing.
See image: left hand side original, right hand side modified.
Hoses now run between valve covers and the air boxes just below the filters.
No more smoking..
75A66B9C-3B9A-406F-BA7C-701AEE792D8E_1_201_a.jpg

FWIW,
I would never do that!! Seriously!!
Your modification really hasn't done anything, other than eliminate the Positive Crankcase Ventilation on one side of the engine!
Eliminating the RSV (check valve) and moving that line to the other side of the Filter & MAF only provides a path to suck oil vapers through the filter & Hot Wire MAF Meter, (Not Good - Like using K&N oiled Filter) as that will destroy the MAF.
Eliminating the Manifold Vacuum from the MBV makes it useless.

The oil vapers from the head/crankcase need to be pulled into the intake track and nothing else is acceptable.

Your modification may have provided an observation that the exhaust white smoke problem is solved, but is the "tell"; you have yet to find the real cause of the oil smoke.
Work arounds usually cause more problems that they solve...

I suggest you use the mod to troubleshoot?
First use/build a manometer (reply #37) to test & record crankcase negative pressure. Make the loop in the manometer at least 24" with 6" water and only place on the oil filler cap when measuring CC pressure.
Swap the engine bank with the mod - use all the same parts. - Test CC pressure and engine smoke!
Then swap the MBV & RSV used in the mod - Test CC pressure and engine smoke!
Learn anything?

[LappingLuke]

Yeah that is most definitely not the move. The crankcase under vacuum will be drawing unfiltered air from that location into the valve train. All that dust kicked up by cars in front of you is going to float right into your engine via the cold air duct in the bumper.

[m6bigdog]

Yeah that is most definitely not the move. The crankcase under vacuum will be drawing unfiltered air from that location into the valve train. All that dust kicked up by cars in front of you is going to float right into your engine via the cold air duct in the bumper.

#1 reason not to to that modification!!