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Old 09-07-2016, 11:40 AM   #1
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Can an engine force oil through a good AOS?

Is there anything that can go wrong inside the engine to force oil through the AOS? I put a new one on 2000 miles ago and I'm burning through 3 quarts of oil. I've done leak down and compression tests with good numbers. I replaced the PCV valve on the driver's side. I check crankcase pressure and it's perfect at 5 inches. I cleaned the outlet part of the AOS to the engine intake and ran the car for a few minutes and it was full of oil again. So my really only last option is to buy another AOS even though the crankcase pressure is perfect. And I'm not sure the dealership will accept a return of a product that still kinda works but just passes a crap-load of oil. Not sure if it has any warranty anyways but I'll raise hell about that.

Grrrrr!

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Old 09-07-2016, 12:26 PM   #2
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If your oil level it too high (over filled), the AOS can pass liquid oil into the intake.
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Old 09-07-2016, 02:20 PM   #3
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JFP,
Could a wild ride 'swamp' the AOS if the engine is only slightly overfilled? I am thinking about the oil in the shallow sump getting violently sloshed around .
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Old 09-07-2016, 02:36 PM   #4
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It's usually not the oil in the sump, it is the oil in the cam covers that is the issue.
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Old 09-07-2016, 02:46 PM   #5
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Thanks for the clarification JFP. So I'll correct it.
A "wild ride" with abnormal high G forces could cause the AOS to become temporarily swamped and cause excessive smoking.
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Old 09-07-2016, 03:11 PM   #6
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It can, these engines are known to hold a lot of oil in the cam covers at speed, which is why the high performance versions in the 996's known as the X51 package used extra oil scavenging pumps in the cam covers and a "northwest passage" oil line to get the oil back into the sump.
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Old 09-07-2016, 04:01 PM   #7
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Oil level is definitely not high. Especially since I'm burning it...it's almost always too low!

And no wild rides to work...haha.
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Old 09-07-2016, 04:09 PM   #8
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Could this symptom be from a scavenging pump failing? This would allow the oil level to become excessive in the head and the AOS could pull liquid. I wonder if this is an issue especially regarding the recent question regarding smoke bombs during left turns.
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Old 09-07-2016, 04:37 PM   #9
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Quote:
Originally Posted by JFP in PA View Post
It can, these engines are known to hold a lot of oil in the cam covers at speed, which is why the high performance versions in the 996's known as the X51 package used extra oil scavenging pumps in the cam covers and a "northwest passage" oil line to get the oil back into the sump.
Thanks for this explanation. I did not know this about the X51. I had only read the 'sexy' parts of the X51 kit - sports exhaust ,extra mystery power and cost. I have never seen a comprehensive list of all the X51 differences. The extra scavenge pumps and N.W. passage certainly seem desirable and rather inexpensive to have made a standard feature.I understand why it would be expensive as a Dealer installed retrofit/option.
But for the P.O.'s question it does hint at an (unlikely?) cause
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Old 09-08-2016, 02:01 AM   #10
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Quote:
Originally Posted by 911monty View Post
Could this symptom be from a scavenging pump failing? This would allow the oil level to become excessive in the head and the AOS could pull liquid. I wonder if this is an issue especially regarding the recent question regarding smoke bombs during left turns.
Good possibility.....
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Old 09-08-2016, 02:05 AM   #11
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Thanks for this explanation. I did not know this about the X51. I had only read the 'sexy' parts of the X51 kit - sports exhaust ,extra mystery power and cost. I have never seen a comprehensive list of all the X51 differences. The extra scavenge pumps and N.W. passage certainly seem desirable and rather inexpensive to have made a standard feature.I understand why it would be expensive as a Dealer installed retrofit/option.
But for the P.O.'s question it does hint at an (unlikely?) cause
The X51 "kit" is a $15K item just for the parts, and includes new cylinder heads, making it a very expensive add on as it requires dropping the engine and a PIWIS.

As mentioned above, I would look at the existing scavenging pumps before getting exotic.
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Old 09-08-2016, 06:12 PM   #12
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This is the thread I was referring to where the OP talks about smoke on the left handers that got me wondering about the scavenge pumps, especially on bank 1. I know installing incorrectly is easily done and was going to suggest checking since it is easily determined if installed correctly or not. Apparently incorrect installation was the problem and could be an issue with this one as well. The thread attached shows how to identify. Hope this helps.

Huge Smoke Screen From My Boxster At a Track Day
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Old 09-09-2016, 07:36 AM   #13
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Is there an easy solution to checking the health of the scavenging pumps?

Car also seems to be making more startup noise than usual. Not that oil consumption might be related or anything.
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Old 09-09-2016, 07:54 AM   #14
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If you could describe or record the start up noises it may help diagnosis. Noting the oil grade used in your engine may lure the undesirables into the thread, so keep it quiet ?
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Old 09-09-2016, 08:18 AM   #15
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Quote:
Originally Posted by patssle View Post
Is there an easy solution to checking the health of the scavenging pumps?

Car also seems to be making more startup noise than usual. Not that oil consumption might be related or anything.
If this were mine the first thing I'd is get under the car and make sure the pumps are clocked correctly. There is no pressure test etc. that can be done. They are easy to remove and inspect though.
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Old 09-09-2016, 06:10 PM   #16
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What year is your car? I had an 01 boxster s with the same problem. Replaced aos, cam plugs, spark plug tubes, lifters. And it still would happen. I have an 06 boxster s now, autox and track it and have never had the problem.

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Old 09-09-2016, 06:12 PM   #17
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Originally Posted by patssle View Post
Is there anything that can go wrong inside the engine to force oil through the AOS? I put a new one on 2000 miles ago and I'm burning through 3 quarts of oil. I've done leak down and compression tests with good numbers. I replaced the PCV valve on the driver's side. I check crankcase pressure and it's perfect at 5 inches. I cleaned the outlet part of the AOS to the engine intake and ran the car for a few minutes and it was full of oil again. So my really only last option is to buy another AOS even though the crankcase pressure is perfect. And I'm not sure the dealership will accept a return of a product that still kinda works but just passes a crap-load of oil. Not sure if it has any warranty anyways but I'll raise hell about that.

Grrrrr!
Porsche parts carry a 2 yr warranty. If it's filling with oil I think it will be covered.

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Old 10-04-2016, 05:56 PM   #18
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Finally got to inspect at least one scavenging pump - not sure exactly how they go bad it's just a metal piece turning. The other is at least installed correctly from the outside - looks like a PITA to remove.

I think I'm just going to replace the AOS again and see what happens.
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Old 10-05-2016, 06:41 AM   #19
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The chances of a pump actually failing have got to be pretty tiny.

Removing the pump wasn't that bad. It looks like it would be easier than replacing the AOS.
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Old 10-05-2016, 07:47 AM   #20
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There is one more remote posibility: aos relies on a small return than can be partially obstructed, when you remove the aos put a hose in the tiny hole in the block, and blow with your mouth to see if is free
Maybe an old aos seal or something, if not draining fast you can have almost half quart of oil up there ready to be sucked into the tb, however I vote on another bad new aos

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