CaymanPower

I went back to the Sixties and converted the GEN2 Cayman PCV system into a 'road draft tube'.

I disconnected the crankcase breather line from the intake manifold (PN: 9A1 107 515 01) and also the vent hose from the AOS to the intake manifold (PN: 9A1 107 520 01). Thus, i do NOT have any connection what so ever from the AOS to the intake manifold, meaning that NO oil can enter the intake tract and seep into the cylinders via the AOS. The respective intake manifold inlets are both sealed.

In order to still vent the crankcase i connected a 'road draft tube' to the AOS outlet (intake manifold side) that goes under the car, and have sealed the crankcase breather line (intake manifold side) but allowing some 'fresh air' entering a little hole (the size of a needle) to still vent the crankcase through the heads. This way the AOS works like a 'catch can' which can return the oil droplets to the sump while it routes the vapors directly to the atmosphere via the 'road draft tube'... Do i smell oil outside the car? Yes i do!

The question is... does the exhaust still smoke upon cold startup?

YES! Car works perfectly (although i do NOT recommend this mod) but it STILL smokes upon cold startup - same HUGE cloud. So, the conclusion is obvious: on the GEN2 base Cayman the AOS is NOT responsible for the smoke.

From where do you think the oil is coming up? Any ideas?

Karl02832

I have yet to see any smoke when I start my car (hot or cold).
You sure it is oil smoke? How "huge" is huge? You sure it is not in your mind?

Macster

If the smoke is oil smoke it can still come from oil residue in the intake. However, the smoking should be brief and diminish/fall off very quickly.

If the smoke is oil smoke are you sure the engine's not overfilled with oil? I know the AOS is out of the loop (well, not entirely and I'll cover this below) -- I certainly hope this mod is nothing more than a test mod and not intended to remain active for any length of time -- but an overfilled engine can move enough oil past the rings to smoke.

Also, not having an AOS connected means the crankcase runs with too much pressure and this internal pressure can force oil past the rings on those cylinders that are not on their compression, power or exhaust strokes.

In short what you have done may have traded oil smoking caused by the AOS's presence (and defective operation) for oil smoking caused by the AOS's inoperability.

Sincerely,

Macster.

CaymanPower

Hi Karl,

Believe me... it's HUGE, a big cloud. It seems to be a trait of the GEN2 base Caymans. It's my second GEN2 base Cayman and both smoke badly. It's far from normal. At this point one thing i'm pretty sure it's NOT from the AOS (air-oil separator). Occasionally, the oil is entering into the cylinders and showing up ONLY upon cold start-up. There is only two possibilities that i'm aware of... either the oil is seeping through the valve seals and guides from sitting, or through the piston rings. In either case it doesn't result from wear. We are talking about very low miles engines here.

What car do you have?

Karl02832

I have a 2011 spyder. No smoke on start up and I have put around 2000 miles on it in 2 months.
Seems like you are lucky enough to pick out the cars with problem huh?

CaymanPower

Hi Macster,

It's blue smoke, definitely oil. The smoke occurrences pattern (or lack of it) is the same either way: AOS IN and OUT of the loop. The engine is NOT and never was overfilled with oil.

This is only a test although the engine revs as freely as before. If the crankcase would run with too much pressure i wouldn't reach the same speed flat out on 6th gear at the same point and on the same road. Also, if the internal pressure could force oil past the rings on those cylinders that were not on their compression, power or exhaust strokes it was more likely to see the smoke when that pressure was maximum - engine hitting the redline and then left to overrun.

Tell me what you think.

CaymanPower

Unfortunately i'm not alone. DFI's engines seem to be NOT affected by this BIG cloud of smoke upon cold start-up, only the 2.9L is.

Dryslick13

Do the new models use an AOS? Looks like they have a breather system with a pump and crank case vent.

Macster

I'm not as familiar with the 987 engines as I am with 986 engines but I daresay in this regard they are similar: Some smoking -- oil smoke -- on startup is normal. Frequent smoking upon startup is a bit out of character. Prolonged smoking persisting "long" after the initial engine start is not normal. Excessive/persistent/prolonged smoking has almost always been due to a failing AOS. (I've gone through this twice with my 02 Boxster. That is I've had to have 2 AOSs replaced. And at the end consistent heavy oil smoking was the last symptom to appear.)

Absent any other symptoms or signs of distress: the smoking is not prolonged (just a brief though at times a rather large cloud of smoke is ok), no CEL on, oil consumption normal, no rough idle, no hunting idle, no excessive vacuum at engine idle to the point the oil filler tube cap can't be removed against the pressure difference; the smoking upon startup is nothing to fret about but of course one must keep an attentive eye on the engine just in case.

I don't like disconnecting the AOS. There are I believe much better ways to eliminate or confirm the AOS is the cause the smoking.

The pressure build up won't slow the engine down any. It can't begin to have the effect the pistons moving in and out of their bores has on the air inside the crankcase and the drag this produces. As one piston moves down the cylinder -- away from the head -- it pushes a considerable volume of air ahead of it. There is another piston beginning its journey up its cylinder -- towards the head -- and this makes room for the air being displaced by the cylinder on its down stroke.

This represents drag and lost hp which is why for instance F1 engines have many scavage pumps. The desigenrs want to run the crankcase at a very low pressure. This reduces the loss of hp this air movement causes and of course keeps oil out of the air which makes of the air heavier and presents even more hp robbing drag to the rotating/reciprocating parts.

The lack of a properly functioning AOS can overpressure the engine and cause various seals to perhaps begin to seep. Hopefully they will stop once the AOS is reconnected and properly functioning. Furthermore, in the case of your car's engine, the AOS is important because it helps keep pressure reduced in the engine crankcase which lowers the boiling point of water and unburned gasoline and helps keep the build up of water and unburned gasoline in the oil down.

If you are convinced the AOS is not the cause of the smoking then you should reinstall the AOS and look elsewhere for the cause of the smoking.

Perhaps a ring has broken or a valve stem seal has failed. (I don't recall the history/background of your complaint, so I'm assuming the oil is of the proper type and viscosity rating?)

You say the engine is not overfilled? Have you tried draining the engine oil and then adding say 7 or 8 quarts (less then then the capacity of the engine) and then checking the oil level to ensure the oil level indicator is reading accurately?

Sincerely,

Macster.

CaymanPower

Macster,

Let me start to say that i found the crankcase breather line connecting to the intake manifold very intriguing, in that both the breahter and the AOS vent are subjected this way to the intake manifold vacuum. In a closed PCV system such as this, 'fresh air' is supposed to be fed to the crankcase via the breather line in one end and then crankcase vapours drawn from the crankcase by the intake manifold vacuum in the opposite end. So, i must assume that a positive pressure differential exists somehow between those two opposite ends in the intake manifold.

In fact, at WOT - blow-by worst case scenario - the AOS renders itself more or less unuseless because there's too little or NO intake manifold vacuum to pull the vapous out of the crankcase. Just like with a 'road draft tube' it's the high crankcase pressure itself that allows the vapours to escape. A lot of race cars vent the crankcase directly to the atmosphere and only have a 'catch can' to trap the oil. The only drawback is emissions. There's no drama here and no smoke either.


Such as?


And yet, Porsche has several TSB addressing this same issue regarding different car models, the base GEN2 Cayman included.

Macster

Under abrupt throttle opening -- and how abrupt this can be we can't know because we can't know how quickly e-Gas opens the butterfly valve -- pressure will rise in the intake manifold system. But as the engine gains rpms the pressure drops and there once again exists a good pressure difference between the intake manifold and the connection with the AOS and the connection which allows fresh air into the crankcase.

While I grant you the pressure difference is not as much as it is during idle it still helps to minimize the pressure build up in the engine crankcase.

Not sure I follow you: There is IIRC one TSB out that involves if my memory is any good a DME update. This update (WAG) probably involves delaying turning on the injectors a bit longer (or possibly turning them on sooner) and possibly revising to what degree the VarioCam variable timing is advanced or retarded at engine start and after and when the VarioCam variable lift is enagaged or disengaged.

My point is that if Porsche has solved this smoking upon start up issue then why not just apply whatever fix or workaround is covered in the TSB? Why even bother going to the trouble of disconnecting the AOS?

Sincerely,

Macster.

CaymanPower

Simple... because the DME update did NOT solve the problem nor did the AOS replacement. Now we can definitely forget about the AOS because the problem isn't there. That's my point.


Why do you think there's a relationship between the oil smoke upon startup and the variable intake valve lift mechanism?

CaymanPower

Macster,

When connecting the AOS back to the intake manifold i've found out that, in fact, the crankcase breather line does NOT connect to the intake manifold but to the oil filler tube which goes under the intake manifold. Thus, there's NO clean source of 'fresh air' to ventilate the crankcase. Just wanted to correct what i said earlier.

Macster

If a TSB exists for the smoking upon startup and it involves a DME reflash -- I don't recall where I heard this maybe from my Porsche tech friends -- then there' s not much a DME reflash can do but fiddle with injector timing, injector pulse widths, VarioCam timing and lift (if car equipped with VarioCam Plus).

Just thinking out loud: Perhaps the new DME lets the engine crank a few more revs before it enables the fuel injectors and throws in some adjustments consisting of some combination of valve timing/lift tweaks only upon startup of shortly after which will help evacuate the oil in the chambers and lower the amount of smoking upon startup or possibly eliminate it entirely.

I'll see if I can learn anything more about this from my Porsche tech contacts.

Sincerely,

Macster.

Macster

Ok. I had a reason to visit Porsche dealer today. Took my Boxster in for oil/filter service and when it was ready spoke with my of the techs.

Asked him about Cayman S smoking upon startup.

He said that some do, some don't. In some cases if the engine develops a smoking problem AOS is suspect, provided always oil level is ok and oil proper type, does not have a lot of miles on it, etc.

He said it can take a bit of time to work oil out of the intake after an overfill or a bad AOS.

If AOS ok and there are no other possible causes -- oil level, etc. -- then the engine is just a smoker.

I asked him about a TSB for this smoking and he said he knows of no TSB or recall or campaign regarding smoking upon startup.

I'd say if you're sure the AOS is ok and the engine's not overfilled with oil and the oil's the proper type and grade etc. and doesn't have like a gazillion miles on it then hook the AOS again to the engine and drive the car. And avoid looking for smoke.

Sincerely,

Macster.