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Here's a post referring to oil in the air box caused by the positive crankcase ventilation system and its seperator - there's a few more on the forum.

Yes, I have read most of them, but my biggest question isn't so much what to try...the hose, but exactly how to get to it and how long it will take.
 

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2015...typically premium, and often ethanol free, particularly in the colder months but often mid-grade. I never put in regular unless that is all there is.
I have now taken apart the airbox and most of the hoses...


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Shining a light in the funnel/cone shows it to be clean and clear from all 3 points: inside the airbox, where hose #4 attaches and where hose #6 attaches.

Hose #6 is completely clear. I can easily blow through it and see light coming through it (albeit around some twists). One potential issue, and maybe is is OK, is the fitting to which the other end of hose #6 attaches (pictured below)...it swivels and feels loose. Is it supposed to be that way? I've noted that this looks different than the parts diagrams and different than photos posted by others where the others have the hose connecting directly without the plastic elbow fitting.

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Hose #4 appears to be clear but I can only get one end free...not sure how to release the clamp on the end not attached to the airbox. Any tips on that? Is the tool pictured a special tool needed to release the clamp?

Or if the other end looks clear, is it likely OK?? I stuck a screwdriver into the other end and it came out with only minor residue but a blockage could be father in. The other pictures I've seen seem to have shown crud caking up at the end near the funnel and I don't have any of that.


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What else should I check?

The odd thing, and probably just purely coincidental, is that the smoking started occurring right after and oil change (not overfilled) where I changed to using Castrol instead of Amsoil. Any chance that there was some interaction with the two oils that may have lead to oil in the airbox? I wouldn't think so, but just putting it out there.
 

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There's two separators, the cyclone one attached to the air box, and one inside an aluminum cover.

I haven't had any issues like this, so can't talk from experience, but guess either of these separators could cause oil to be deposited in the air box - I'd rather check both separators than get into a compression test.

 

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Hose #6 is completely clear. I can easily blow through it and see light coming through it (albeit around some twists). One potential issue, and maybe is is OK, is the fitting to which the other end of hose #6 attaches (pictured below)...it swivels and feels loose. Is it supposed to be that way? I've noted that this looks different than the parts diagrams and different than photos posted by otherer where the others have the hose connecting directly with the plastic elbow fitting.
I can't find that fitting on BMW DVD - I'd put the hose onto that and blow & suck to see if its clear, or if it behaves like a PCV check valve.
 

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There's two separators, the cyclone one attached to the air box, and one inside an aluminum cover.

I haven't had any issues like this, so can't talk from experience, but guess either of these separators could cause oil to be deposited in the air box - I'd rather check both separators than get into a compression test.

I've seen this diagram and references to it before. I haven't seen something that looks like this. Where do I find it?
 

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From the BMW DVD - Oil Separator
Ouch...that is some very serious surgery. That may be more than I want to tackle.

Any ideas on diagnosing whether the separator is causing the problem without all that? Perhaps plugging certain hoses to eliminate that as a problem? I'm wondering if isolating the crankcase vent hose into a temporary container would show if the oil is being forced from blow-by vs being siphoned due to a plugged separator?
 

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I think its worth trying your suggestion of temporarily routing the crankcase breather tubes to a can, or even as I've seen on some Harley's a small filter at the end of the vent tube discharging to the ground while ensuring it wont get onto the rear tire.

I wouldn't plug anything and potentially over-pressurizing the crankcase.

A lot less PIA compared to tearing into the oil separator or pulling the plugs for a compression/leak-down test.



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So, I am a member of the "oil in the airbox" club, too. 2013 GTL, 40K on the clock.

Mine started after the replacement of a coil. During this project, I also did an oil change and replaced the spark plugs. As part of my oil change routine, I checked the airbox drain and it was dry. I am wondering what the correlation is. What did I do incorrectly that would lead to oil in the airbox? I am 95% certain that the air pipe did not suffer any cracks. I'm not even sure that a cracked air pipe would or could cause oil in the air box, as I am not sure of how exactly it works. But, I am certain that this issue started after I had the front disassembled, since I did check the drain tube and found it dry, as it had been every other time I had checked it. I have not had enough in the airbox to cause any smoke. I found the issue because I noticed that the end of the drain tube was "wet". I pulled the plug and got a fair amount out, maybe 3 or 4 oz. I have only put slightly under 2k on her since the coil replacement and in total have maybe drained 8 to 10 oz out of the airbox. Most of the miles have been fairly spirited.
 

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Finally got my bike back from the shop a few days ago. There diagnosis was similar to the plugged hose situation. They felt that the hose (#9 in the diagram in post 5) was defective and was collapsing and getting pinched off. So, the ordered a new one from Germany. After many weeks of waiting for it to arrive, it did...but only about the time I headed out of the country for 3 weeks.

I had previously verified that hose #6 and the funnel were completely clear before I took the bike in to the shop.

The problem is NOT fixed. :(

Here's were I am...

I can do the steps in post #4 and get nothing over and over. So, I think they means my pistons are good.

If I start with a drained oil condensate hose and ride for about 35-40 spirited miles I get smoke. I head home and find that the condensate drain produces about 13-14 ounces. After draining it, I head out again and, after the initial burnoff, I get no smoke at all. Then, after another 35-40 spirited miles, it smokes. I head home and find that the condensate drain produces about 13-14 ounces again. I've done this cycle 3 times and under similar riding, the distance over which the airbox fills up is roughly consistent.

About 1 ounces per 3 miles is getting sucked/blown into the airbox. Given that the post #4 test does not produce smoke...at least not unless the airbox is already full, where is the oil coming from???? My shop has no idea.

Looking at the diagram, it seems the hose they replaced was the drain back into the oil reservoir. I don't know if they checked the other part of the separator (the 2nd diagram in post #5). If it is actually where it is blocked and the problem is just that the oil isn't being permitted to drain, is it normal for that much oil to make it into the airbox to start with? Seems high to me.

Can oil get forced back up that path? If not, I suppose hose #6 is coming from the crankcase and that could be the source. If you were to block off hose #6 separating it from the airbox, would it be harmful to the engine? Would it be a reasonable test to run with #6 plugged to eliminate it as a source of oil? Since others have had trouble with #6 plugged, I wouldn't think that would be helpful...but I don't know.

What if I blocked off #9 so that it couldn't drain back into the other separator. Any thoughts on that as a way to eliminate the possibility of oil being forced back up into the back from the oil return line?
 

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Sorry to hear that the cure is eluding you.

In the past day or two someone posted a few good pics and description of what they did with the breather system and it cured the same symptoms you have, BUT I just cant find that post now - I'll keep searching just in case there's something in it that could help.

Edit:
Here's the post I was referring to.

 
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