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There seems to be some confusion over the direction of the check valve in the breather system. The vast majority of photos online seem to show the valve in what I think is the wrong direction. I think this is the wrong direction:
I think the correct direction is as shown below:
Reasons for this:
The diagram in the EPC seems to show it in this direction (although not very clear)
The metal joiner between two of the tubes shown above is a "Fixed Orifice Tube" PCV device. This device allows a flow of a high pressure gas into a low pressure gas at a low flow rate. The hose clamp I think would be used on the high pressure side of the device to stop the hose blowing off, while the low pressure side can simply use a ribbed fitting. The fluid would flow from the high pressure to low pressure side as represented in the second photo. I have one of these check valves at home with me, and I tested the flow direction of it, it allows air to move from the flat side to the conical side.
The other part of the breather system is located on the rocker cover, it is tube, A 271 016 04 81, it is connected to what seems to be an oil separator built into the rocker cover. This indicates that this is where gas from the crank case exists to enter the intake air stream. This means that the three tubes and check valve don't actually carry gas from the crank case to the intake but rather carry fresh air to the crank case (breather). This supports the idea that this is the correct orientation of the check valve.
What if the valve is installed the wrong way:
I think the check valve would stop fresh air entering the crank case, when the crank case builds a positive pressure it will still vent air in the crank case to the outlet on the rocker cover gasket, bu no new fresh air will enter the crank case and may lead to build up of sludge and contaminants in the oil. It doesn't look like it would cause any other problems as no metered air leaves the system...
If I have missed something and got this wrong please let me know thanks
Last edited by zubin3333; 11-08-2019 at 10:46 AM.
Reason: I found some new info that made the old post wrong
That's a very interesting thing you discovered there, will definitely have a look at mine.
Have you turned your check valve around and can You share your experience after doing so? Any issues, leaks, pressure build up, etc, etc.
I wonder if that's just a factory error when they ware building the engine and for some reason it just went unnoticed by the QA, or if perhaps it's just how it should be, but there is something we don't quite understand how and why...
Hopes that OP is still around, or somebody else has actually did it, and is also willing to share WIS of before/after.
It's weird because looking at the diagrams for the breather hoses, and the check valve, it does actually show that it's suppose to be the way OP described it.
With the flat part of the check valve to the left, and the cone shaped part facing right.... Now it's even more confusing,
Mistakes are made, that's certain, now, the question is... Is it the diagram that's false, or the actual installation?
This is basically the same setup (give or take) we have in the M271, except our "pcv" line feeds directly from the crankcase instead of the valve cover.
Crankcase ventilation system
Notice both lines feed from the crankcase towards the intake plenum.
I would agree with the last post that the diagram shows the check valve pointed towards the crankcase and not away from it. However, the diagram in this post would suggest that the check valve be pointed away from the crankcase.
Last edited by slammer111; 07-24-2020 at 11:46 PM.
That's a good find, and here is a good quote from the same article:
"The gasses flow out of the PCV port and into the intake manifold where they are sucked back into the engine to get consumed and pushed out of the exhaust. Simple enough."
This quote alone verifies that the check valve orientation is incorrectly displayed on the diagram, but correctly installed on the engine(check valve is pointing away from the crankcase)
I'll be replacing my crankcase breather hoses in the near future anyways (fume leak in the vicinity). Will install it the same way they did during the recall in 2008, which I suspect is with the check valve pointed away from the crankcase. In any case I'll post some pics when the job is done.
Last edited by slammer111; 03-16-2021 at 06:17 AM.
I'll be replacing my crankcase hoses in the near future anyways (fume leak in the vicinity). Will install it the same way they did during the recall in 2008, which I suspect is with the check valve pointed away from the crankcase. In any case I'll post some pics when the job is done.
Must have missed something... What recall in 2008?
Anyways, will expect the pictures, interested to see what you've found, but I also guess that it will be pointing away from the crankcase, which is the correct orientation imo after reading through the article you've shared.
So many things makes so much sense now, lol. Thanks.
It's by country and there's a possibility it has already been done on your vehicle if you bought it used. I'm doing mine again because something is leaking and spewing fumes from there. Suspect either a cracked hose or check valve.
Last edited by slammer111; 03-16-2021 at 06:13 AM.
If you think about it, it would make no sense to install a valve towards the crankcase. Why would the crankcase ever need additional pressure? There is already enough extra air simply from blow-by.
Before installing, I blew into the new check valve to see which way the air flowed. It is towards the cone side. Yes, there is the word "Motor" and some arrows pointing towards the cone side (the arrows also show the airflow direction). See photo below - the markings are visible.
On a side note, notice the brass nipple with the tiny paper clip sized hole. To be honest I'm not sure why they had to use such large hoses if the air is going through the pinhole restriction anyways. When servicing my engine, the hole was partially caked with carbon. I had to poke out all the excess, with a paper clip of course.
New crankcase breather hoses and check valve with cone side facing away from crankcase, which allows air to flow out of crankcase through valve into throttle body
As mentioned in my other post, this was also the same orientation my old (failed) check valve was installed by the dealership as part of a recall.
Last edited by slammer111; 03-09-2021 at 09:52 PM.
As in my OP, my thoughts are that these tubes are for slowly introducing fresh air to the crank case and that the "exhaust" from the crank case is through the oil separator on the rocker cover. But that photo slammer added definitely contradicts that idea. Still, I don't know what one is to make of the Fixed Orifice Tube or the choice in placement of the hose clamp, if that picture is correct.
For anyone interested, I have actually installed the valve with the cone facing the crank case in July 2019 and so far I have had no problems. If it weren't such a massive pain to get to, I might have actually done some testing with both orientations to work out what is going on.
Now that you know yours is in the wrong direction, this would be a great opportunity to take some notes then swap the direction the valve and see if there are any changes in performance. I would recommend buying a new valve though. Those things are brittle.
11-06-2019, 10:02 PM
