Back to where I started...

[911hillclimber]

Jeff: I can't be alone with this problem?

Zuffenhaus have done a full diagnostics test on the car when I involved them on the problem and they found nothing as a result.

Last service they commented how well the car ran and of course it had not smoked with them, but the car arrived hot, I waited for the service and drove home. They drove it to the MoT station, again, commented how "sweet" the car went.

I now use Shell 95 octane, have done for months, before always Shell 99 octane. Tick over the same with both fuels.

Take you suggestion about an additive to clear things as long as the cats will cope.

This car has so many positives, but this smoke and the coolant loss is testing my loyalty of 32 years with Porsche.

More returning issues with the coolant level drop, after filling the coolant to Max and 380 miles last week in Wales, the level is bellow Min...

 

[hotfrog1]

I found this on a Google search. It is on what looks like an Official Porsche China website. I did not find a EU or USA equivalent.

https://www.porsche.com/china/en/accessoriesandservice/porscheservice/serviceandorgininalparts/maintenanceandparts/fueladditive/

The product is Keropur available on Amazon UK website:

https://smile.amazon.co.uk/KEROPUR-Petrol-Extra-Additive-Germany/dp/B071HXZQY8/ref=sr_1_2?dchild=1&keywords=keropur&qid=1595781527&sr=8-2

 

[Motorhead]

Graham,

The Shell fuels have some decent additives so I wouldn't expect there to be any benefit in using an additional additive, but it's worth a try at this stage.

If you're not seeing any obvious coolant leaks (I assume that you've done both cap replacements already?) it would be worth getting the system pressure tested. If that doesn't throw up any external leaks then I suppose head gasket replacement would be the next stage, and if the heads were off the bores, valves and valve stems could be examined which could give some clues ref the smoking issue, but I'm sure you don't want to go there.

If you have replaced the coolant caps recently, there was some chatter regarding ill-fitting caps on the Cayman forum recently:

https://www.porscheclubgb.com/forum/tm.aspx?m=1060603

Probably worth checking if this is related to your leak? I can't find the post but I'm sure Richard Hamilton chipped-in with further information related to getting a compatible cap and expansion tank.

Jeff

 

[911hillclimber]

Both caps were replaced about a year ago, OPC parts.

when I check the small aos pipe, I'll see if there is any obvious cap leaks by the engine.

Boot located cap seems tight, no residue anywhere.

the off beat idle has been with the car since I had it about 4 years ago

 

[911hillclimber]

Just found this:

OK - Your E-gas, this could be either an air leak in the induction or the throttle body needing a good clean, however, when inspecting the air induction trunking its impossible to tell unless you take it apart so its better to just do the whole job at the same time as cleaning the throttle body. The butterfly in the throttle body gets gummed up with dirt and oil creating a thick viscous fluid that sticks to the butterfly on throttle closing, the throttle motor opens and closes the butterfly in relation to your throttle input, when closed on decelleration it sticks, as the engine revs fall to tickover levels the throttle motor slightly opens the butterfly to maintain tickover - but because of the sticking it cant do that easilly so it applys more power to the motor which then opens the butterfly a bit too much and has to close the butterfly again - which sticks again - this causes the hunting, Its like a car that wont tickover having to have the throttle applied everytime the engine revs lower to the point of stalling. The reason for the gum is the AOS - it feeds an oil mist from the oxidised oil in the engine crankcase to the induction system to burn the mist off - this is perfectly normal but this mist does leave some residue over time in the throttle body and impurities in the inducted air stick to this mist and create the sticky gum. ( this usually takes a few years to build up) To rectify, disconnect the air induction pipes and remove the throttle body (You can clean the body without removing but its a fiddly job, takes longer and you cant be sure you have cleaned all the areas completely) To clean the throttle body just use brake fluid (but dont splash it on paintwork as it will crinkle the paint and remove it) A good rub will remove the gum and make the throttle body shine- the main part you need to clean is around the butterfly and the surface around the butterfly especially the stepped part of the body where the butterfly sits into. (Its like a door sitting into its jamb) Reassemble and use a tiny amount of vaseline to lubricate the rubber induction tubing before putting together and securely tigten the clips. (Rubber grease is better but its expensive and not that many people have this stuff lying around so vaseline is a good alternative) The vaseline will also ensure a good seal between the rubber and the joints If its the first time you have done this job it will take a few hours

 

[Motorhead]

Graham,

I remember reading that link a little while ago in connection with a similar rough idle problem and it had dropped off my radar. Bearing in mind your AOS issues it could be worth checking-out while you're in the engine bay looking at other things.

Jeff

 

[911hillclimber]

Yes Jeff, bit of a strip-down, but might well be the time to delve deeper.

Took the car out today, it has been 5 days standing on the flat.

Started up smoke free. Good beginning.

Ran it for about 8 miles, filled up and then a further 6 miles to a local National Trust.

Wondered around for about 2 hours, back to the car.

Started it, a small amount of smoke, lasted about 2 seconds, but visible. Engine was at 60C so I presume cold enrichment was dialed in by the ecu. It was a small smoke discharge, nothing like the 'normal' smoke screen James Bond would be happy with.

Wife said if we sell it, it won't be replaced.

Shame, it looks great!

 

[911hillclimber]

Made an hour this morning to have a check of the oil in the AOS 'outlet' vent pipe.

Started the car to move it close to the garage, NO SMOKE on start up; been standing for 3 days.

Warning light came up on the dash: coolant level.....

Got the pipe off. Found the note I made that I changed this AOS in early Sept 2019, so about 10 months in.

Stuck my little finger in the pipe outlet tube of the AOS and got oil, not a smear, not a whisper, but oil. More than I expected.

Less so in the pipe, so flushed the pipe generously with brake cleaner rattle can which has a high velocity blast, ideal. Washed a fair bit of oil out. The pipe is corrugated, so lots of oil traps, so doubt I got it all. Flushed it in both directions and let it dry in the hot sun.

Rammed a cloth onto the AOS to catch any more oil, but the cloth came out almost dry.

Cleaned the rear drains while the top was 1/2 up, silly not to, last dome a month back, strainers covered in small leaves.

Put it all back together, the 3 pipe clips snapping into position with a good 'click' so sealed.

Poured a litre of coolant into the system, still not full, so guess what I'll be doing soon.

Started the engine, sounded good, no smoke and took it for a very short run to settle it down so to speak.

So: what to conclude from this? Not sure to be honest, maybe fit a 5th AOS?

 

[Motorhead]

Graham,

I don't think you've any choice other than to fit yet another AOS at some stage, unless you can think of another reason why oil is getting into the tube. Rather odd that while you found a lot of oil in the tube there wasn't any in what I assume to be the diaphragm chamber area? Obviously the corrugations in the tube will help to trap oil, whereas I would guess that the inside of the chamber containing the diaphragm will be smooth and maybe if the car's been standing for 3-days any oil present has drained to the bottom and your cloth didn't reach it? It's both very odd and frustrating that your engine displays a propensity for destroying AOS units for no apparent reason!

Perhaps it's a bit pointless but maybe the first thing to do now is to keep a detailed record of usage and immediately the engine starts smoking to check for the presence of oil in the AOS outlet tube to confirm that the AOS definitely is the culprit and proceed from there.

A litre+ of coolant for top-up doesn't sound great if there are no obvious external leaks. Ho-hum..!

Jeff

 

[AndrewCS]

I assume that the AOS is 15 … and that it connects to the intake via hose 4 … which is a ~ horizontal run ?

The hose from the crankcase bleeds` connects below the intake, does this feed into the intake ?

Forgive the obtuse trait here, trying to relate a few things together including your `rough idle`

 

[AndrewCS]

More detail …

 

[911hillclimber]

Those diagrams are as close as I could get a few days ago to the AOS, looked at the manuals on Boxa.net.

Yes, that is the AOS and 4 is the vent tube with a Y piece close to the inlet just before the throttle body. There is a pipe opposite each other at the lowest point, the majority of the run is indeed horizontal and then slopes to the throttle body area.

This is the tube I removed and flushed out this morning.

the main inlet to the aos is from the engine goes up to the diaphragm of the aos, droplets gather and when big enough drips back to the engine sump.

on the dry dry side of the diaphragm is the outlet to the vent pipe.

some in the States have removed the vent pipe, blocked the 2 inlets on the inlet housing and take the aos end to a tank that is open to atmosphere, race cars have this breather system.

if there is oil in the vent it will be caught in the catch tank and can be emptied at will.

Thus, no oil will get to the inlet manifold!

oh how tempting this idea is....

 

[AndrewCS]

Thank you Graham.

Catch tank … part of my thinking too, have run them on older, high revving VAG engines … catch more condensed water than oil which = emulsion. I also ran the engine oil level at half full to reduce crank pick up and hence load on block breather - venting system.

I still ran the catch tank outlet to the intake as vacuum is required to `draw` on the block breathing process.

Items 5 & 8 … are I assume a type of baffle box, initial restriction on block venting … maybe one is faulty allowing excess volume through ?

What does the hose 3 connection to below the intake do ?

 

[911hillclimber]

Not sure what #5 actually is, but seems to align to a cam shaft(?)

As with all modern engines, loads of pipes everywhere, must be part of an intricate balancing act perhaps.

There is just the one vent tube from the AOS to the inlet.

The inlet must reach low pressure which I would expect to hold the valve in the AOS/diaphragm shut, ie no air passing/no oil passing.

Trying to imagine the role of the vent tube to the AOS diaphragm to the wet side of the AOS.

As to the catch tank:

I too had thought the tank would simply be in-line with the vent tube and not open to atmosphere as in a normal race engine, but any oil would come down the vent tube, drip into the catch and the vent continue to the inlet manifold.

Could be made such that access is via the cover behind the seats so you dont have to faff about with the hood propping etc.

As an experiment, the pipe could be made from a donor vent tube off ebay etc and jubilee clips.

Easy DIY task.

Would prove a point but not find the cure!

 

[AndrewCS]

Thanks … more thinking required on my part !

 

[911hillclimber]

There is a 'valve' in the diaphragm as in this cut away of one of my dead AOS's, the central disc, about 15mm dia that is biased across by the light spring. However, this must simply be to balance the panting movements as there is no passage from the wet side to the dry unless the peripheral seal or diaphragm fails.

When I took this one apart there was a 'well' or puddle of oil resting at the bottom of the dry side where oil had escaped through the seal, the dia' was perfect.

 

[AndrewT]

Graham, I think you should experiment with the catch tank idea. It’s something that I considered when I had my smoking 2.9 Cayman, but I don’t have the same engineering skills as you. I’m waiting excitedly to hear the outcome of your experiment.

 

[AndrewT]

When I cut away my old AOS (2.9 Cayman) there was oil on the “dry” side too even though the diaphragm was intact. I’m not the one who fitted the new AOS so I can’t say whether there was any oil residue in the various connections.

 

[911hillclimber]

Yes, worth a few hours of messing about!

Read this just on the Type911 web site:

9A110704200 9A110704201 9A110704202 For all Gen 2 Boxster & Cayman and all 981's. Oil Separator. One of the most common failures in the modern water cooled cars is the Air/Oil Separator, also referred to as the AOS. The AOS is basically a small diaphragm distillery which distills the minute amounts of oil mist in the crankcase, liquefies it and sends it back to the crankcase. The “clean” air is now sent into the air intake (after the throttle body) to be burned off by the engine. When the AOS starts to fail it cannot separate all of the oil out of the mist and some liquid oil is sent to the air intake. A few drops of oil is enough to generate the GREAT SMOKE BOMB for which our cars are famous for. A big smoke bomb once in a while is completely normal, due to the architecture of the flat-6 engine, which may let a drop of oil flow into one of the combustion chambers sporadically.

 

[911hillclimber]

Mind you, £20 off ebay, how can you go wrong?

Only need the spare vent pipe to cut up and adapt to this catch tank, looks perfect!