Ordered and replaced an AOS from Pelican parts approximately 2 months ago due to excessive smoke on acceleration. Oil residue was excessive in the entire intake system. 8-12 hour job removing it from the top, cleaning everything out and reinstalling the new parts including the AOS vent tubing, top and bottom. Well just drove it today and it's smoking excessively again. Very frustrated. Is this a sign of a defective external AOS or could the internal AOS'S be bad as well? It's also leaking oil from the bellows again and running down the front LH side of motor after replacing it with new parts and OEM clamps. I've driven the vehicle at least 400-500 miles since I replaced it. It literally looked like a crop duster aircraft today like before in September. When I hit the gas heavy today at around 5000 rpms it reoccured. As soon as I let off the gas pedal, smoking subsided rapidly and after an additional 10 miles it never returned. Does it seem that the new Porsche OEM AOS is defective or that the internal AOS's could possibly be bad? No oil residue or excessive carbon build up on the exhaust tips as before. Any and all suggestions would be greatly appreciated!

 

Maybe the smoking wasn't from a failed AOS but from some other problem?

Smoking heavy at high RPMs is not an AOS failure symptom I'm familiar with (with my Boxster). Smoking at idle or smoking all the time with maybe a CEL is my experience. And in not too many minutes of the onset of smoking the engine was running so poorly I dared not let it idle any more let alone try to take up to 5K.

Is the oil level ok? Is the coolant level ok?

You sure you got the AOS installed correctly and all the lines/etc hooked up right?

While rare an AOS can be bad out of the box or fail shortly after installation. Porsche parts come with a warranty which protects one against getting a bad part off the shelf or having it go bad shortly after being put in service.

You might visit this site:

http://www.pelicanparts.com/techarti..._Separator.htm

and try the vacuum test to see if you can clearly ID a bad AOS.

 

Thanks for the quick response. Everything was hooked up correctly by technical data. I certainly will do the vacuum test now. Just royally sucks that I have to tear it all apart again to reacomplish this. The smoking only exists for the first minute after startup then disappears. If I let it run and throttle it up and down until achieving operating temp, it stops smoking from exhaust. Driving normally around town and highway is fine with no smoke. That's until I really get on it coming up the mountain and around turns spirited. She really smokes then. Then as quickly as it appears, I let off the throttle and it slowly goes away. Engine idles fine always. No missing and no CEL. No excessive oil consumption. Exactly the Same thing as before I replaced it in September. What exactly does the internal AOS's do? Just wondering if they are defective and prematurely wearing out the external AOS? I did notice today that it was whistling when I first started it. Supposedly a tale tell sign of the AOS bad. Oil cap is semi difficult to remove. Certainly has suction effect when removing with motor running. Then it sputters and idle smooths out somewhat. Then when cap is put back on everything is fine. Engine has lots of power. Coolant level good since draining and filling from first AOS replacement. No signs of mixing together. Just makes me wonder if the internal AOS is bad.

 

Not sure what you are referring to when you refer to "internal AOS".

There are the anti-foam pots (swirl pots) which are fed by the scavenge pumps and are designed to remove air the pumps put into the oil before this oil is then routed to the oil tank/sump.

The AOS is designed to remove oil from the crankcase fumes as the fumes flow from the crankcase to the intake through the AOS. The AOS is shaped inside like -- at least the one I cut apart is like this -- a nautilus shell -- which causes the fumes to swirl around in a decreasing radius space. This "slings" the heavier oil vapor droplets out of the crankcase fumes and these droplets collect on the AOS walls and as the oil resumes its fluid like state it can can then run down and rejoin the rest of the oil.

The whistling can be a sign of a bad AOS. What can happen is it results in the crankcase being subjected to too much low pressure and this can result in air being pulled into the crankcase past a seal. The RMS I think is the seal although the front main seal is also a possible source of air. Even a healthy AOS can cause a vacuum leak past a worn out oil filler tube cap to that's another source of an air leak. Regardless the air creates a noise, a moan is what I recall it most often being described as soundling like but I guess a whistle is also a possibility.

'course, the whistle can be from a bad water pump or possibly a bad accessory drive idler/tensioner roller bearing, too, to name a couple of possibilities.

When my Boxster experienced its first AOS failure (it is up to #3 now) the failure resulted in the engine being flooded with oil. Flooded to the point the engine locked up when the tech tried to crank the engine for some reason. Thankfully the engine suffered no harm.

When the car was ready to pick up the SM told me it can take some driving before all the oil is "flushed" from the engine's intake and exhaust.

He said it could take as many as 50 miles of driving. He drove the car some and when I picked it up it didn't smoke.

I don't recall the 2nd AOS failure aftermath but the 3rd one the engine smoked like something from another world. The engine didn't suffer any hydraulic lock up but I did notice when I picked the car up the engine smoked a bit upon start up and once or twice on the way home when pulling away from a dead stop.

I just figured it was some residual oil and arranged to drive the car for awhile to get the engine up to temperature and to drive the car in town to heat up the intake manifold to help any residual oil leave the intake.

Oh, as for the cap, my experience with my Boxster is I was able to unscrew the cap without any difficulty but was unable to remove it against the pressure difference. This caught me so off guard I think I turned off the engine and removed the cap just be sure I wasn't doing something stupid.

I wasn't. But it was about this time I decided I was in over my head and arranged to get the car to the dealer for a pro's diagnosis. At that time -- circa early 2004 -- AOS failure was still rare (my 2002 had covered around 80K miles by then) and I had no real experience to go on. I might add though when I talked to the SM and described what was going on he called "AOS" and proved to be right.

Bottom line is there may not be any problem with the AOS -- though that whistling noise doesn't pardon the expression sound too good -- but what you are experiencing is just dealing with an engine (intake) and exhaust that suffered a thorough dousing with engine oil. It can take some time for this to work its way out of the engine (intake/exhaust).

As long as the engine is not manifesting any other signs of a problem, no CEL, rough idle or an idle that goes up and down a bit, and while the engine may smoke at start up but doesn't continue to smoke or doesn't begin smoking at other times and continues to smoke, you might be dealing with the normal after effects of a severely failed AOS that really flooded the engine intake/exhaust with oil.

Check the vacuum though to be sure it is within spec. And try to pinpoint that whistle source.

 

Macster, Thanks for all your help and thorough explanation. I really appreciate it. On all jet engines I have worked and still work, the air oil separator/deoiler principal is the same. Although it's gases are vented overboard after being separated by an impeller (AOS driven by accessory gearbox) by centrifugal force and returns oil back to gearbox or scavenge pump. About internal AOS (at least that's what Porsche calls them in the illustrated parts breakdown) it's hard finding any operating principals for them and their purpose in the engine. Are they more less like a scavenge assist return for the oil that the external separator collects or do they create a vacuum for the external seperator to use for the separation properties? How soon after replacement of yours did yours fail again. I'm only on 2 months after a replacement of the AOS and have driven quite a bit and everything seemed resolved until last Friday when it all came rearing it's ugly head again. I bet I spent 2-3 hours alone cleaning up the excess oil throughout the intake system and now hsve this happen again 2 months later seems ridiculous. Complete teardown again and cleanup. I might remove transmission this time. Probably alot faster than removing the intakes and everything else through the top. Reminds me of working on F-16's which I rarely enjoyed. Just wish I could find a schematic or Theory of operation of that particular system. Thanks again.

 

If by "internal AOS" you are referring to the defoaming pots their function is pretty simple.

The internal structure is a fairly simple cone. (The angle of the cone may be "critical" but I have no info on that.) The wider section of the cone is up the narrower section down.

A line from a scavenge pump feeds oil (with a lot of air in it) to this cone.

The oil/air mixture swirls around inside the cone. The heavier oil collects at the bottom and drains back to the oil sump. The lighter air stays up high and exits another way.

I had a chance to see this in operation, so to speak.

Years ago I worked in an optical lab making eyeglasses. One of my functions was to run a lens generator which was used to rough in the shape of the curves the prescription called for. This process used a diamond coated cup wheel and lots of light oil. Not only were glass lenses processed but so too were plastic lenses. A heck of a lot of glass/plastic swarf was created the result of sometimes removing more than half the lens blank's material.

This oil mixed with the lens swarf drained into a large spinning tub. The heavier material (glass and plastic) was forced by centrifugal force against the wall of the tub while the lighter oil went over the top edge of the tub and was caught by an enclosure. The oil ended up in a tank. The electric pump would then pick up this oil and route it to a special "filter" which consisted of a cone that was open at the bottom. The oil being pumped into this cone would (I could picture this in my mind) swirl around. The finer but heavier particles of glass/plastic still in the oil -- left in the oil by the imperfect action of the centrifugal oil/swarf separator -- would dribble out of the bottom of the open cone filter like some thick pale pasty goop.

The now much cleaner oil would exit via a high pressure line which ran over the connection of the fluid manifold in the lens generator enclosure.

It is the same principle employed by the swirl or defoaming pots in the engine. In this case the good stuff, the oil (sans quite a bit of air) exits from the bottom of the cone while the bad stuff (air though still with some oil vapor in it) exits from near the top of the cone.

I can't say with any certainity the new AOS is bad. All I can offer is that is a possibility. There is also the possibility there was an installation problem.

Regardless the presence of oil as evidenced by the untoward and excessive smoking suggests a possible problem with the AOS or its installation. This must be looked into and the problem found or if the AOS and its installation found OK the source of the problem searched for elsewhere.

 

I had the same smoking on a 996 I bought a couple months back to flip. It would smoke more on hard right turns and above 5000 RPM on straits. No oil leaking or dripping on the floor , but there was a small crack in one of the spark plug tubes that would allow a tiny but of oil to spray and hit the headers at high load/RPM of hard right hand turns. It was a bit hard for me to believe that that much smoke could come from a leak so small that it would not produce a drop on the floor!

 

Had a '96 Mustang GT that leaked oil from a valve cover. The oil leaked only when the engine hot and for a short time after it was shut off. There was never any signs of oil anywhere, that is no oil on the engine or any oil on the ground.

All there was was an odor of burning oil. Later at first I thought it was my imagination (or my subconscious desire to have the POS Mustang burn up) but I'd catch a very brief sight of smoke wafting from under the hood.

Later though it was clear smoke was coming from the engine compartment.

The leak was found by the fact the SM spotted a stain on the exhaust header which was from the oil dripping down.

What was happening is as you might have guessed by now is all the oil was being converted to oil vapor by dripping on the hot exhaust manifold.

Took more visits to the dealer to fix this, finally get the engine oil tight, than one would believe. One of the last times I had just picked the car up and hadn't driven it but maybe just a mile or two when the smoke just starting billowing out from under the hood. I turned around and drove back to the dealer and parked the car right in the middle of the service forecourt. I was hoping the car would catch fire but it didn't.