968s sucking oil into engine somehow???
 

Hi All,

I'm at a loss. I've a 2001 986s which is somehow managing to suck oil into the top of the engine and need some 'out of the box' thinking becuase I don't believe it's the AOS, and virtually every response to anything to do with exhuast smoke is blamed on the AOS.

For starters, I've already fitted a new Porsche AOS, and changed the oil being very careful to ensure it was only filled to half dipstick.

I've had the car about 4 months but used it very rarely until the last 2 weeks since the sun started shining! :)

The symptons seem to be that the car is perfect, absolutely perfect, so long as you don't give it too many revs. I've used it for the last 2 weeks to pootle round town and for work a couple of times (M4, 100 miles round trip), so all is perfect if the car is used 'normally'.

However, if the car is used with some 'spirit', oil is getting somewhere it shouldn't. Last night I went out for dinner, had a chance to use the car on some A roads and enjoyed giving it a bit of stick, up to 6K revs a few times. Left the pub an hour or so later and there was a cloud of smoke at start up, for about a minute. Then, on the way home , gave it some revs , in third, on a dual carriageway and there was a drop in power and an almighty eruption of smoke out the exhuasts... enough to totally obscure over a 1/4 mile of dual carriageway. Lifted off and smoke cleared, carried on home. Then this morning, start car up and 30 secs of thick white smoke. And I know it'll do that a couple of more times as oil seeps down into the engine over the next day or so as this is not the first time it's done this!

This is about the 4th time and explains why I've already changed the AOS and the oil. It only happens when the the revs are high and underload. It's as though oil is being sucked up into the top of the engine (I mean the inlet side of things) when the engine is working hard, and then either getting into the pistons to burn off there and then, or being 'stored' to allow it to slowly seep down ino the engine to be burnt off the next time the engine is started.

it displays none of the sypmtons of the AOS on the way out, no vacuum etc,,, and the oil is only half filled so no overfill possible.

I can only think maybe there's some kind of half blocked tube or something in the inlet/emmissions side of things that's allowing oil to get where it shouldn't during hard engine use. But I don't know where to even start to look!

Probably explains why the car has had a few owners recently, not much point having a Boxster if you can't give it some every so often! :) And I suspect the last few owners have given up trying to fix it.


Any ideas anyone? I know some people have had this happen to them once, and then never again, but this is 4 times for me and I'm not finding any kind of technical reason for it.

Cheers all for any advice. :)

Piersman

Piers...
You don't mention your cars mileage, but if its high and maintenance has been neglected, piston rings and or bore wear usually cause the symptoms you describe.

1) For a quick check of the AOS, can you remove the oil fill cap easily when the engine is idling - if there is suction there and cap is hard to remove, its a good indication of a failing AOS.

2) Did you thoroughly clean out the plennum chamber (where the throttle body is situated) when you replaced the AOS?? There has been quite a few instances where there is a lot of old oil resedue coating the inlet system after a bad AOS.
There has been instances on this board where new AOS's have failed almost immediately.

3) Has your oil level dropped since you replaced it?

4) I'm assuming you have no intermix in the oil or coolant resevoir.

5) Do a search on AOS and get ready for an hours worth of reading.....

If all else fails, you should do a compression or leakdown test to check ring / bore wear.

I've seen a few posts where someone had replaced their AOS and the new one has been bad right out of the box. Apparently replacing it is no guarantee of solving the problem.

This may not be what you want to see (and may not apply since the example in this blog had tons of track miles) but the boxster in this blog post was exhibiting the same sort of issues, which turned out to be rings and bores, which was revealed by doing a compression and leakdown test.

Boxster Projects | Engine Rebuild / Replace

Steve

Thanks for the swift replies all. The car has done 72K miles apparently, but who knows how true that is or how it was driven during those miles.

With regards to the AOS, in theory it could have been a bad one fitted, but the car doesn't display any of the classic AOS going bad symptoms and the car doesn't smoke in the slightest between the extreme 'episodes'. It didn't blow any smoke after the AOS had been replaced for days and days so I don't think there's any oil loitering around the top of the engine since then.

Hmmm.. that last post sounds remarkably similar though, mainly my car seems to have done the smoke trick after a sharpish left turn off a roundabout or such. I'm not sure why a left turn combined with worn pistons / rings should trigger a smoke bomb, but it seems common.

Looks like I need to possibly get the condition of the pistons/rings checked then, maybe 1 or two of them are leaking allowing oil to get sucked in at high pressures. What's involved with a leakdown test, will any competent specialist garage be able to do that?

Bypass the AOS and recheck. Put a plug in the intake side where the hose goes into the intake. reroute hose to a container or vent to atmosphere with clean rag to contain spillage or forced oil. Do not seal off this end! Drive like this a while to see if symptoms come back. This is not a fix just a way to drive car home after a AOS is busted or to test the system to see what area the oil is coming from.

Even though you may think the AOS is good this will tell you if the oil is coming from the AOS because it is forced out here due to blowby or other means.

Bypassing the AOS valve Air Oil Separator on a Porsche Boxster - YouTube

^^ Great suggestion from healthservices!

Ahhhh.. Hi HS, I thought I recognised your name, I found your thread from about 2 years ago earlier this evening, and it's what I have with mine. The symptoms are spot on and everything seems to agree:

Lots of acceleration through and out of a left hand bend, causing oil to collect at the back right hand side of engine, an overwhelmed scavenger pump not clearing oil quickly enough allowing it to get into the AOS and then up into the air intake side of things. Which would explain why the day after an episode, I get 30 secs of smoke as the oil that has seeped down into the engine overnight from the air intakes gets burned off.

Has your replaced scavenger pump continued to do the job and prevent a re-occurrence?

Is it easy enough to swap out the rear pump with the engine in the car?

I had wondered about just isolating the AOS, although I'm tempted just to replace the oil scavenger pump and then see what happens. I'm confident from your earlier thread that this is the issue. Assuming you've found it to have fixed it permanently! :)

I did try and post a reply last night, not sure why it's not turned up. Strange, this one turned up ok. Ok. I'll try again! :)

Hi HS, thanks for the reply. I found your superb thread from 2 years ago where you were investigating the same issue. Your symptoms were exactly as mine is doing:

Car is perfect if driven normally , but when given some revs particularly off a left hand bend it coughs a huge volume of oil smoke out the exhausts, and then for the next couple of days there's 30 secs of smoke at start up as the oil that has found it's way to the inlet airways seems to work it's way down to the pistons over night.

This all fits with your findings of the oil being pushed to the back right hand side of the engine during cornering, allowing too much to be ingested into the AOS and then liberally distributed amongst the air intakes assemblies; for the majority of it to be chucked out immediately and the residue to drip down slowly over a few days.

All makes perfect sense and sounds spot on! :)

Was the scavenger pump the final solution for you? Is it something that can be changed easily enough with the engine in the car? Is there anything else that could be preventing oil returning from the head quickly enough?

Thanks for that previous thread and the detailed pictures etc... it just made so much sense compared to anything else I've found! :)

Replacing mine helped but I'm still at a loss as to why as the pump looked perfectly good in every way. Yes the pumps can be replaced with the motor in the car.

Yes I had problems with the site too yesterday.

Oil pumps wear very little as long as they just see good clean oil. I would check for fouled sparkplugs starting with cylinder #2 in the middle right side.

Hi HS, did you ever get an answer as to why your oil in the head wasn't draining back down to the sump with the car at rest? There was a discussion on one of your threads where the question was raised but the answer was never clear. I can understand that a small'ish amount of oil will always remain in the head but your engine seemed to have a lot in the effected side based on the pictures you posted. Shouldn't that have drained back to the sump (albeit slowly) once the engine was turned off?

I ask because I can see me taking the rear scavenge pump off this weekend and being covered in oil as it pours out the hole from behind the pump! :)

Cheers

Oil will not be returned to the sump without the aid of a scavenge pump. This is due to the design of the head and the fact that the engine is horizontally opposed. Oil can be drained back to the chain wells but will puddle there in some amounts if only sitting static.

Also, Scavenge pumps are high enough in the cylinder head that they can be removed with very little oil loss.

In my experience the smoke that is emitted from these engines when cornering IS NOT the fault of a scavenge pump. I see this condition routinely and have only had a scavenge pump replacement dove it in the instances where a scavenge pump has failed. These failures only occur when a pump sucks debris from another failed component into it, thus seizing the tightly internal clearance pump and breaking the drive tang off completely. This results in a mechanical disconnecting of the pump from its drive and also generally has other symptoms, like exhaust cam retardation on the afflicted bank that can be great enough to make valves contact pistons and bend them.

An example:
Timing chain failure shed a portion of chain roller. Scavenge pump inducted this, pump seized and drive tang snapped.
http://www.flat6innovations.com/25bo...s/DSC_0010.JPG

And here are the damaged pistons from valve timing retardation allowing exhaust valves to contact pistons:
http://www.flat6innovations.com/25bo...s/DSC_0009.JPG

There are lots of dynamics behind each of the 27 modes of failure I have documented, with primary and secondary failures along with collateral damages extending from each. If I had to bet, you are not seeing a scavenge pump deficiency.

I totally agree.

However in my case, I find it totally odd though that after a period of idle and after another hour of the car sitting, there was a incredible amount of oil that came out of the passenger side valve cover. I don't remember the exact amount but thinking back I think there was over 4 quarts that drained out of the valve cover when I removed it.

I would think that under normal idling there be enough pumping action to remove what oil there is puddling in the passenger head???

Is this normal?

How long had the engine sat when the cam cover was removed? I see no way that much oil could reside in the cam cover, the chain well area would dump it straight back to the sump, even if a pump didn't exist.

If the chain well has a common area that drains oil into the sump is the opposite true? Oil from the sump is draining out into the chain well while the car sits? The valve cover also covers part of the chain well. Maybe the 4 quarts I saw was from the chain well???

Dunno just a question as I'm not familiar with the oiling and return circuit.

This was the quote from back then...

Yes, the oil that you drain was in the sump, the chain well shares sump oil to a certain level. This is why draining oil is the first part of an IMSR procedure or cam cover reseal.

Interesting, I wonder if a trap door or restriction in that port or doorway could lead to less AOS issues. Because With The AOS removed you can clearly see a whole lot of oil being thrown up the AOS port in high RPM situations. The AOS for whatever reason is directly above the chain.


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The AOS is internally baffled.

What kills the AOS more than anything is oil selection coupled to extended oil service intervals that kill the membrane inside the AOS.