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DanHoug
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Joined: December 05, 2016
Posts: 5831
Location: Bemidji, MN
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 Posted: Thu Jun 06, 2024 3:03 pm Post subject: Re: Crankcase breather idle theory |
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quite the interesting read and data! thanks for your work on this, Chris. some comments...
- i wonder what the highest vacuum in the intake boot is?
- since you tested with the bottom sealed and found 2-3" Hg activated the diaphragm and hence air valve closure, this would mean that the entire crankcase would need to be at 2-3" vacuum. how often does that really happen? during during periods of trailing throttle when there is the least blowby, there is also the least intake boot vacuum to create that crankcase vacuum. or is it activating on crankcase pressures created by piston movement, fluttering away with each stroke?
- as you pointed out, the breather is NOT closed at idle. i don't see how VW could have even imagined that to suggest it as its operation. it really WOULD be useful to see a video of this installed on a WBX with the dynamics of crankcase pressure on the bottom side and intake tract vacuum on the top-- affected by manifold pressure, AFM flap resistance and air cleaner resistance all at changing volumes and velocities of air as load and RPM change. my suspicion is that this valve closes FAR less of the time than we envision!
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60% of what you find on the internet is wrong, including this post.
'87 Westy & '89 Westy both 2.1 4spd
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tencentlife
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Joined: May 02, 2006
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Location: Abiquiu, NM, USA
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E1
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Joined: January 21, 2013
Posts: 8380
Location: Westfalia, Earth
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| Posted: Sat Feb 17, 2024 1:53 pm Post subject: Re: Crankcase breather idle theory |
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Thank You (!) for your efforts!
I’ll try to post more, but for now here’s an incomplete thread I did on this very concern:
https://www.thesamba.com/vw/forum/viewtopic.php?t=786142
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1984 Westfailure/2.1 Digijet/5.43 Ring & Pinion/Peloquin/D-rated BFG KO2s
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montanasurfer
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Joined: March 06, 2014
Posts: 326
Location: United States
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| Posted: Sat Feb 17, 2024 1:47 pm Post subject: Re: Crankcase breather idle theory |
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Hello Everyone,
I've decided to read these 9 hellish pages and provide a summary. There are some great minds on this thread and I am grateful for all their hard work to try to understand this system. This thread gets referenced quite a bit regarding the diagnosis and understanding of the breather tower. I've probably read it 10+ times and am still not 100% sure as to how this system works. However, I want to summarize everything to the best of my understanding. So hopefully this summary can be helpful to others to understand this system.
The breather tower function:
The valve operation will never be directly affected by the engine inlet vacuum. That vacuum is to be found downstream of the throttle butterfly, in the plenum chamber and manifold pipes; but the tower breather valve will never will see that vacuum. The spring is below the diaphragm and pushes it up off the end of the J-tube. That means that the valve only closes off if vacuum is very high on the breather hose over to the intake boot. That vaccum there is only going to be at all substantial at mid-throttle cruising conditions. There is zero vac there at idle, and zero at WOT (Tencent made measurements that confirm this). That valve will close as soon as the engine starts and remain so throughout the operating range, except for opening during idle and WOT.
(Sources Tencent and JWPATE)
Breather tower anatomy:
| JWPATE wrote: |
The hole at the bottom of the outlet pipe is solid with crud and not even oil would pass through it.
This is the top section and the diaphragm is all but gone to pieces. I did blow through the square vent hole before cutting the top off, and I knew the diaphragm was bad because I could hear air blowing right through the tower.
This next photo is all I could retain of the original diaphragm.
And I show this view because you can see at the tip of that scribe the slot in the plastic top which communicates the square vent hole with the upper diaphragm chamber.
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| JWPATE wrote: |
To find the hole which vents the upper chamber to ambient, look under the upper lip. I noted that it was square shaped on the new tower, but on the original it is round. Both are in the same location however.
And the same view from a little closer in.
This photo is from the top, with a sheet of paper to show up the vent drilling.
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| davideric9 wrote: |
Breather towers are back in stock, although I understand these are aftermarket made in China. I'm concerned that the new towers do not have a vent hole on the atmosphere side of the diaphram. Is this a redesign? an error in reproduction? my inability to understand this part? does this repro have a diaphram at all?
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What a faulty breather tower does:
Possible cause of high oil consumption:
| Wildthings wrote: |
I can't say I really understand what happens on a Vanagon sealed crankcase system. Except for minor variations in flow all the blowby has to be drawn or forced into the intake air system at all times or the crankcase would see quite high pressures. If the pressure were allowed to climb then you would get oil puking out of every available crack, seam, seal, and orifice. What I think the valve may do is prevent surges in air flow from the case to the intake as the throttle opening changes and prevent the case pressure from dropping below atmospheric, in which case fresh air could be drawn through leaks in the case and mess up the idle intake mixture. I agree that a failed or failing blowby valve is a likely cause of bad idle and off idle performance.
I think the explanation in the page on Emissions Control that Dog posted is probably bunk. First off the valve never sees intake manifold vacuum, it sees vacuum up stream from the throttle valve not down stream. Second from looking at the pictures of the valve 10c posted it looks to me like the valve is most likely regulated by crankcase pressure and not be intake air system pressure. As I said above except for minor variations all the blowby has to pass into the intake air system at all times.
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| JWPATE wrote: |
It would seem reasonable to expect that such a clogged up breather would not only cause engine idle problems, but also cause case pressure buildup during higher engine operation. Do you have oil leakage from that engine? It would certainly seem likely
Moreover, the issue of sludge blockage in the outlet pipe seems more and more likely to me. With the almost certain deterioration and rotting of those original diaphragms after all these years, added to the oil vapors and sludge buildup – it does seem likely that at least partial blockage may be present in more old, original towers. In such a case your engine case will have been venting itself also past the dipstick seal, valve cover seals, crankshaft seals and so forth.
If one wishes to check whether the case is breathing through the tower or not, go out and take off the oil filler cap with the engine at idle. That will introduce an air leak large enough to lean out the engine to a rough, rough idle. It probably will die. A lesser air leak, such as an old, hard or split hose between the tower and rubber boot will have a similar effect, just smaller in scale.
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Cause of faulty Idle:
| rhpaw wrote: |
| Yellow Rabbit wrote: |
| RHPAW, did you get the new breather installed, and did it fix the problem? |
Like a champ...Out of the box comes the new breather. ....I hooked it up with new gaskets and tube anyway and buttoned the system back up.
Startup proved well, and idle is now rock solid... |
| Wildthings wrote: |
| Hero419 is correct, air leaks in the case are the same as air leaks elsewhere in the intake air system, they cause a lean mixture. If when you replaced the breather your idle changed noticeable then that would be a sign that you have leaks somewhere else in your crankcase, most likely a valve cover gasket or a leak in the oil filler tube area. With a good breather the case will still see a slight vacuum, just not quite as much of one as it see with a failed breather. |
| Wildthings wrote: |
If you are not having problems don't worry about it. The O2 sensor will usually cover for any minor changes in mixture a bad diaphragm might cause while under way. If you feel that a bad diaphragm is giving you an erratic idle then do the following. a. Fix any air leaks in the engine case, b. add a 5mm orifice if you don't have one, and c. add a 22uf capacitor to the AFM. |
Diagnosing a Breather tower:
| JWPATE wrote: |
Yes indeed, a vent opening (square shaped) is clearly present under the left side lip of the upper tower. It occurred to me that if I suck and blow into this little vent it should be possible to create either vacuum or positive pressure inside the upper diaphragm chamber, and thus cause the valve to close and open. It works and requires surprising little pressure to close that valve. If I blow gently into the square vent, I can feel the diaphragm immediately close off and I can no longer blow into the vent. This is just what one would expect, only the pressure required is surprisingly little. But guess what? If I suck on that vent hole and create a vacuum, I can sense the valve open and I then can hear air rushing in from the lower tower (large) chamber. Somehow the vent hole communicates with the main chamber under open valve conditions. Probably there is a simple flap somewhere on the diaphragm to accomplish this. I hope my old tower will answer the question when I cut it open. Doubtful though, as it is the original and probably little remains. In any event, this is the ONLY way I know of at present to test whether the damper is intact and operating without cutting the thing apart. |
Summary of the Summary:
A failed breather tower fails in that the valve's outside diaphram ring disintergrates and the inner ring seals the j shaped pipe closed when positive crank case pressure occurs. When excess crankcase pressure is caused, oil will leak out of other seams such as valve cover gaskets or other seals.
A failed breather tower has a miniscule impact on the idle. Idle issues are typically due to air leaks into the crankcase from other areas.
Van's run just fine with failed breather towers as the ECU and O2 sensors compensate for the breather tower failure.
Unanswered questions
Can anyone confirm that replacing a breather tower will decrease oil consumption?
If breather towers fail in a closed position, how is it that the intake boot and throttle body can still be covered in oil?
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bevelhead
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Joined: April 10, 2009
Posts: 33
Location: Tasmania
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| Posted: Sat Aug 08, 2020 2:27 am Post subject: |
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| tencentlife wrote: |
I've had a Provent hooked up with drainback since early this year and although it had only a small effect on oil usage with this engine, it does intercept all the oil mist and water so the intake tract stays squeaky clean. Oil mist taken in with the fuel-air charge is a heavy contributor to detonation, so that by itself is a good reason to add this simple system.
Initially I did not put in a drainback line so I could hand-drain the trapped liquid to see its composition; it was consistently 2/3rds water, 1/3 gassy-smelling oil. In all likelihood the bulk of these fluids were intercepted during warmup periods.
Once I had a solid take on what it was catching, I went ahead and added a drainback line to a banjo fitting screwed into a modded oil pressure relief valve plug, with Mann's recommended check valve immediately below the separator vessel. So now it's a closed-loop system that requires no regular maintenance or intervention. The filter element inside the vessel should probably be replaced at some long interval, but these units are so new that last I read their literature, Mann doesn't even have a recommended interval for that yet. |
So how is this vent set up going? Any update after 6 years? |
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Merian
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Joined: January 04, 2014
Posts: 5212
Location: Orygun
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| Posted: Mon Jun 08, 2015 6:18 pm Post subject: |
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you suspect a vacuum leak?
why not start a thread just on vacuum leaks?
you can post a list with pics of all hoses you have tested - incl. the one near the m/c... |
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porterbrown
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Joined: February 25, 2005
Posts: 718
Location: Bentonville, AR
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| Posted: Mon Jun 08, 2015 6:15 pm Post subject: |
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| Wildthings wrote: |
| porterbrown wrote: |
| Wildthings wrote: |
| It looks like your breather may have a few extra holes in it, which would constitute a lot of little vacuum leaks. You could clean it up and tape over it with electrical tape, or smear it with silicone. This might be a good place to use the self fusing silicone tape. |
Thanks!
I pinched the hose to the intake and oil started to ooze out of the cracks shown in the pic of the tower. Is this typical (not the cracks....but oil passing through the diaphragm?)?
I've smeared the cracks with silicone and currently waiting for it to dry. |
Your diaphragm is probably shot, as most seem to be, but so long as your crankcase is well sealed having a bad diaphragm doesn't seem to cause problems. |
alright, so a test drive says that sealing the cracks made no change. Also, after sealing the cracks, I did the pinch test again. no change in idle with hose pinched (running to intake). oil found a way to escape through the top-most connection at the oil fill tube with hose pinched
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Wildthings
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Joined: March 13, 2005
Posts: 52538
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| Posted: Mon Jun 08, 2015 5:55 pm Post subject: |
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| porterbrown wrote: |
| Wildthings wrote: |
| It looks like your breather may have a few extra holes in it, which would constitute a lot of little vacuum leaks. You could clean it up and tape over it with electrical tape, or smear it with silicone. This might be a good place to use the self fusing silicone tape. |
Thanks!
I pinched the hose to the intake and oil started to ooze out of the cracks shown in the pic of the tower. Is this typical (not the cracks....but oil passing through the diaphragm?)?
I've smeared the cracks with silicone and currently waiting for it to dry. |
Your diaphragm is probably shot, as most seem to be, but so long as your crankcase is well sealed having a bad diaphragm doesn't seem to cause problems. |
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porterbrown
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Joined: February 25, 2005
Posts: 718
Location: Bentonville, AR
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| Posted: Mon Jun 08, 2015 4:46 pm Post subject: |
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| Wildthings wrote: |
| It looks like your breather may have a few extra holes in it, which would constitute a lot of little vacuum leaks. You could clean it up and tape over it with electrical tape, or smear it with silicone. This might be a good place to use the self fusing silicone tape. |
Thanks!
I pinched the hose to the intake and oil started to ooze out of the cracks shown in the pic of the tower. Is this typical (not the cracks....but oil passing through the diaphragm?)?
I've smeared the cracks with silicone and currently waiting for it to dry.
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Vanagon Nut
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Joined: February 08, 2008
Posts: 10498
Location: Sunshine Coast B.C.
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| Posted: Sun Jun 07, 2015 8:31 pm Post subject: |
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Right. My suggestion may have been hasty.
Plug hole at intake elbow, leave breather hose open?
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1981 Westy DIY 15º ABA
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porterbrown
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Location: Bentonville, AR
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| Posted: Sun Jun 07, 2015 8:27 pm Post subject: |
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10-4. No issues with doing this test while driving? My issue peaks during driving conditions...not idle.
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Wildthings
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| Posted: Sun Jun 07, 2015 8:26 pm Post subject: |
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It looks like your breather may have a few extra holes in it, which would constitute a lot of little vacuum leaks. You could clean it up and tape over it with electrical tape, or smear it with silicone. This might be a good place to use the self fusing silicone tape.
Last edited by Wildthings on Sun Jun 07, 2015 8:27 pm; edited 1 time in total |
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Vanagon Nut
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Location: Sunshine Coast B.C.
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| Posted: Sun Jun 07, 2015 8:02 pm Post subject: |
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pinch off the hose from breather and see if things improve?
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1981 Westy DIY 15º ABA
(VW Gas I4)
1988 Westy DIY 50º ABA
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porterbrown
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Joined: February 25, 2005
Posts: 718
Location: Bentonville, AR
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| Posted: Sun Jun 07, 2015 7:34 pm Post subject: |
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Great thread. A shot in the dark here, but I've been having a helluva time tracking down an issue with a van chugging off the line (under load), and this thread makes me suspicious of my breather tower. Disconnecting the O2 sensor seems to clear up my issue, though testing has eliminated the O2 sensor and coax from the list of culprits.
I've noticed before how my breather tower has always had this sort of mangled top portion....as if the PO had tried to pry off the "cap" once upon a time. ...And it's covered in a nice film of oil.
I assume it's damaged and should be replaced, no? Does it look/sound like this could be associated with my running issues?
Thx for the help!
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tencentlife
Samba Member
Joined: May 02, 2006
Posts: 10151
Location: Abiquiu, NM, USA
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| Posted: Tue Dec 23, 2014 10:55 am Post subject: |
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I've had a Provent hooked up with drainback since early this year and although it had only a small effect on oil usage with this engine, it does intercept all the oil mist and water so the intake tract stays squeaky clean. Oil mist taken in with the fuel-air charge is a heavy contributor to detonation, so that by itself is a good reason to add this simple system.
Initially I did not put in a drainback line so I could hand-drain the trapped liquid to see its composition; it was consistently 2/3rds water, 1/3 gassy-smelling oil. In all likelihood the bulk of these fluids were intercepted during warmup periods.
Once I had a solid take on what it was catching, I went ahead and added a drainback line to a banjo fitting screwed into a modded oil pressure relief valve plug, with Mann's recommended check valve immediately below the separator vessel. So now it's a closed-loop system that requires no regular maintenance or intervention. The filter element inside the vessel should probably be replaced at some long interval, but these units are so new that last I read their literature, Mann doesn't even have a recommended interval for that yet.
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teej
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Posts: 906
Location: Seattle
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| Posted: Fri Jun 20, 2014 6:15 am Post subject: |
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I bought one of the new towers back in December or so. After installation I started noticing more little oil weepy seeps at various places on this engine. Could just be a coincidence but I began to suspect increased pressure in the crankcase. The diaphragm on the old one was, surprisingly, apparently intact as well as different from the new one so I put the old one back on.
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djkeev
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keithwwalker
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Joined: May 30, 2005
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| Posted: Fri Jun 20, 2014 2:10 am Post subject: |
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I agree, I just got a new tower from one of the big Vanagon vendors, and I really doubt it will work as VW intended.
The key to the whole action is that little vent above the diaphram.
If you test an original Bosch unit, the way to do it is to take it off the engine, then cap the bottom on a flat surface. Then you suck the air out of the tower (from the outlet vent that goes to the S-boot), and you should feel the diaphragm move down and stop; at that point it should get much harder to pull air out.
But this doesn't happen with the replacement unit, the diaphragm doesn't move at all.
I may drill a little hole in the cap top, but it will come plugged up after a while.
Or, I may carefully drill a hole for a nipple up top such that a hose can be connected for a drop - that way it won't clog.
Looking at the Mann ProVent, it looks like an excellent system, because it is cleanable and maintainable. I just may keep the aftermarket tower for ease of hose connecting to the ProVent.
| 1vw4x4 wrote: |
These breather towers may be back in stock but for $80 plus dollars and made in china Its a total waste of money.
Did any one come up with a good solution?
I'm thinking of adapting a Golf/Jetta unit to the vanagon boxer engine. |
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insyncro
Banned
Joined: March 07, 2002
Posts: 15086
Location: New York
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| Posted: Sun Mar 09, 2014 10:22 am Post subject: |
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Plenty of good OEM ones in a box at my shop.
I'll post an ad. |
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1vw4x4
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Joined: June 22, 2005
Posts: 472
Location: Pgh. PA
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| Posted: Sun Mar 09, 2014 10:16 am Post subject: |
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These breather towers may be back in stock but for $80 plus dollars and made in china Its a total waste of money.
Did any one come up with a good solution?
I'm thinking of adapting a Golf/Jetta unit to the vanagon boxer engine. |
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