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  #1  
Old 11-11-2012, 09:12 PM
Marcus Marcus is offline
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Oil dripping from the backside of the Intake Manifold / Knock Sensor Replacement

Dear All,

first of all I have to say thank you: There are very usefull hinds posted about knock sensor replacement. I did read to many posts on my resarch, so don´t know who came up with it, but replacement of knock sensors without removing the manifold worked very well for me, following the guidance given (remove alternator and unbolt & move AC Compressor about 2 inch to the right). Thanks again!

But I did face a new problem (like many others before): Dripping oil comming from the bottom center of the intake manifold. I did find quite some posts touching this topic so I know its common), but I still wonder about the root cause of this problem. Some say its PCV Valve related, but others state they are running with a new one and the problem remains. Maybe by now somebody on this forum was able to nail it down, so I am asking...

Thanks a lot!

Marcus
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  #2  
Old 11-12-2012, 07:59 PM
oab_au oab_au is offline
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Re: Oil dripping from the backside of the Intake Manifold / Knock Sensor Replacement

Quote:
Originally Posted by Marcus View Post
Dear All,

first of all I have to say thank you: There are very usefull hinds posted about knock sensor replacement. I did read to many posts on my resarch, so don´t know who came up with it, but replacement of knock sensors without removing the manifold worked very well for me, following the guidance given (remove alternator and unbolt & move AC Compressor about 2 inch to the right). Thanks again!

But I did face a new problem (like many others before): Dripping oil comming from the bottom center of the intake manifold. I did find quite some posts touching this topic so I know its common), but I still wonder about the root cause of this problem. Some say its PCV Valve related, but others state they are running with a new one and the problem remains. Maybe by now somebody on this forum was able to nail it down, so I am asking...

Thanks a lot!

Marcus
Marcus the answer is easy, the fix is not.

The oil dripping off the Iris valve is coming from the PCV valve, that breathes into a passage that runs across the back of the Iris, to dump the crankcase fumes into the inlet manifold. You may fit a new PCV valve, but it won't fix the problem.

This is that the crankcase breather has a separator to remove the oil from the fumes. This breather set-up is a carry over from the 4 cylinder engines, that doesn’t do this, and gives no problems.

For a "yet to be discovered" reason the 6 cylinder separator can't remove the oil from the fumes so it gets carried to the PCV valve, to drip out the spindle, and back into the air pipe that feeds the throttle bodies, to goo the whole area with oil.

The other associated point, is that the PCV valve closes when the throttle is wide open. There is very little breather outlet for the crank case fumes that will increase, under this full throttle condition. So the pressure in the case increases, to push oil out all the seals and gaskets.

The engine really needs a better oil separator, to remove the oil before it gets to the top of the crank case. Not easy to do with one, that will drain back to the sump. A compromise would be to open the cam cover breathers to feed directly into the air box at the throttle bodies, and fitting some mesh into the small separators that are on the covers.
This will increase the breathing of the case, so that there won't be as much oily fumes coming from the old one.

Otherwise, no idea.

Harvey.
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  #3  
Old 11-15-2012, 06:52 PM
SUPER SUPER is offline
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Re: Oil dripping from the backside of the Intake Manifold / Knock Sensor Replacement

I am thinking this might be my issue.

I am a recent owner and had the oil leaks fixed at the same time I had timing belt replaced. So no oil dripping on exhaust. BUT, sometimes when I stop at a light or shut off the car, it smells like burning oil, or hot oil. Open the hood and I can see/smell hot fumes (sort of like a very light steam) venting from the back of the engine between the engine and the firewall. Does not happen all the time. But if I am pushing it a little going up a hill, it seems to bring it on a little stronger.

I need to take the rear engine cover off and try to look in there. But, not coming from exhaust pipes.

Anyone else know what I am talking about?
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  #4  
Old 11-15-2012, 07:21 PM
davew833 davew833 is offline
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Location: Salt Lake City, UT
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Re: Oil dripping from the backside of the Intake Manifold / Knock Sensor Replacement

There's a cover on the back of your engine behind the torque convertor called the oil separator plate that could be leaking too and dripping onto the exhaust in that area. It's common for them to leak, especially on '94 or newer when Subaru changed the material on the plate from metal to plastic that tends to get brittle and crack over time. Unfortunately, the only way to replace it is to pull the transmission or the engine...
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