996.2 cold start smoke

I have problems with blue white smoke at cold start on my 02 carrera 2 I have changed the AOS two times. The first one was aftermarket which didn't did any difference. It still smoked from the time the engine cranked Then I replaced it with an original one and now it starts to smoke after 6-8 seconds after the engine has started but only left side exhaust. This continues for 2 minutes or so while clearing up. there are no ticking or knocking sounds And the exhaust tips are clean both sides. when I remove the throttle body I can see and feel some oil in the intake. Mostly right side. And the pipe from the AOS is also oily. When I remove the oil filler Cap at idle, when the car is cold, I can feel not very high, but some vacuum and the engine starts to go very rough. When cap is removed warm it feels more like "normal" (very little) vacuum and there is only little change in engine idle. I feel tempted to go for a third AOS change? The engine is running strong and not smoking when driving or at WOT Oil level is in the middle. the engine has done 55000 km after rebuild.

Left side exhaust is Bank 2, right side of engine where the AOS breather hose vents, so it does sound like an AOS problem. It is not that unusual for an AOS to go bad, even a new one out of the box. True test would be the manometer on a modified oil filler cap to measure the crankcase vacuum. There are some threads on here on how to do that and some benchmark measurements. I sure would do that before tackling an AOS replacement project, unless you are not the one doing the work. How old is the AOS now?

Do you drive the car hard right before shut down or are you just putting around?

A bad AOS will smoke all the time. Also isn't there a check where you can have the car running and then remove the oil cap, the car will run rough if there is a problem but a good AOS will compensate quickly and will run smooth. Having a puff of blue smoke at cold startup is normal for a flat-6 as oil can get past and pool which is burnt off at startup.White smoke is just the water condensation in the oil burning off.

Seems unlikely 3 AOS went bad in a row? What does the blue/white smoke smell like? My car smokes occasionally when I move it from the garage, to the driveway, then restart to move it back to the garage. When I do that, I suspect the smoke is fuel or water, and it sometimes looks whiteish. Is it possible you overfilled with oil? Some of these cars smoke on startup. Maybe you have one and there isn�t anything significantly wrong with it?

If you are adding gas additives they will cause smoke on a cold start up.

There could be residual left over in the intake from the bad AOS. Clean out the manifold with alcohol soaked paper towels as best you can and see how it goes.

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+1 This happened with my car

Thanks for the replys I bought the car in august last year in Munich and drove the car home 1100km without any oil use at all. Next morning it started with a huge cloud and I thought, well it's just the AOS I changed it and cleaned all oil out of the intake. After 100km the intake was covered in oil again. Changed the AOS now to a OEM and it helped a lot. It smoked less and less, but then it started to increase again. Now it starts to smoke after 6-8 seconds Idle instead of before where it smoked right from the time the engine cranked. I still gets some oil in my intake. It is not overfilled and I don't use aditives

How did you clean the intake manifold? They can hold a lot of residual oil where the three runners merge so you need to go very deep on both sides. Also use a manometer to measure crankcase vacuum (from the oil filler tube) and it should be around 5 inches of water.

I think my intake plenums are a little to oily. Here is my hand after feeling inside. I have got a spare oil filler cap now and will measure crankcase vacuum.

Mine does a large puff of smoke after sitting for awhile or after hard driving. AOS tests around 5 with my manometer. I do have some oil in the intake last time I had it off. I have not investigated further but curious what turns turns up from this. Could an AOS be bad yet still show a normal reading on the manometer?

Damn things are a bit complicated. They are designed to capture oil in the crankcase fumes, drain the captured oil back to the crankcase and vent the crankcase fumes (ideally without much vaporized oil in it) to Bank 2 and to the Throttle Body (vent lines 4 and 5 here http://www.autoatlanta.com/porsche-parts/hardparts.php?dir=996-99-05&section=104-10 ). The puffs of smoke, oil in the TB and intake plenum, James Bond smoke screens and smoking after hard driving or sweeping right handers are all a result of the AOS being either marginally bad or being totally overwhelmed by oil sloshing around in the crankcase and getting sucked up into the vent lines. The crankcase should be under vacuum, but under certain say hard aggressive driving at high RPM's, there may be much less vacuum which affects the overall performance of the AOS. Normal reading on a manometer at idle may not be indicative of what happens to the AOS under full running conditions. At best it is a crappy plastic device that is a PITA to replace and is the source of great consternation to many. I believe even Jake mentioned one time that he has found new AOS's bad right out of the box. Given the fact it is heated by coolant lines and there is just a cruddy diaphragm separating the coolant/crankcase fumes, there is one more major PITA thing to go wrong. Pretty good read on AOS testing and function https://rennlist.com/forums/996-foru...this-mean.html I would not worry so much about a puff of smoke. It is actually quite normal to have some oil in the intake because of the mist of oil vapor being vented by the AOS. I have a good, functioning AOS, and every time I remove the TB for cleaning I always find a light coating of oil in the intake plenum. It is not normal to have the intake overwhelmed with oil and creating a smoke screen. But, overall, it is still kind of a crap shoot with the AOS.

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I believe I have read posts that the Motorsport AOS will improve this issue but they do not show any greater reliability than the stock AOS. If I recall from prior conversations here on RL some people "in the know" have found the motorsport AOS's fail just as much as the stock AOS...at several times the price. That said I may need to spring for one the next time around. My understanding is the mode of failure of the stock AOS is that the rubber diaphragm gets a hole in it and allows oil thru (along with crankcase vacuum) - Hence the irregular manometer readings when it's failed. Is there a way for oil to bypass the AOS then even if the diaphragm is intact? That would appear to be what is happening on my 996 as it tests around 5 on the manometer. I am running my 996 mostly on the track with track suspension setup and Hoosier R7's. I do have a 2 quart deep sump and run the oil level at the bottom 3 bars as recommended, but still appear to be picking oil up into the intake somehow....evidenced by a big, brief cloud of smoke at startup. Interestingly if I come off track and the car sits for say 1 hour, when I restart I don't get any smoke. If I let it sit for 2-3 hours, or overnight I get a big smoke at startup the next AM.

I don't know if the Motorsports AOS will work on a Mk1. Most say it only is for the MkII engine. Anyway, interesting reading http://986forum.com/forums/boxster-g...s-failing.html

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I have a Mk2 engine, as does the OP in this thread. I have read you can make it work on a Mk1 but it takes some modification of tubing, probably an engine-out project but not sure.

GHere is a video You Tube I think it is wired it’s not smoking imidiatly but after a few seconds. In idle it can take several minutes to clear, but if I drive away imidiatly it clears after a few hundred meters. Oil consumption is about 250ml/ 1000km

There is a small puff of something immediately. Could be fuel or oil or moisture, but it�s there immediately. If the intake is oily, and you�ve changed the AOS, then something else is not working correctly.

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mine too.

I'd do a compression check, possible rings or valves/seals/guides. It could be just normal car issues not 996 specific problems.

Mine was doing exactly the same. Everytime after sitting for a night at cold start there was a puff of smoke appearing at the left exhaust tip after some 5-6 seconds and only for some seconds. They smoke was a bit blueish. Cannot come from oily intake as it is clean and oil-free as the AOS is disconnected from the intake and rerouted to prevent it from the diaphragm being stressed by the excessive vacuum at high rpm when the throttle body closes. So no more too oily cranck fumes in the intake. Last engine out operation when I got a broken intake valve seat on cilinder 3 fixed the only thing that was done on bank 2 was the injectors removed, cleaned and checked. Since then no more smoking starts. Could it be the cause? Also another culprit overwhelming your AOS with oil could be a scavenging pump loosing slowly some of its efficiency. Had this problem recently. At some point oil started to get spitted out by the AOS abundantly. Maybe worth to check?

Silk, how is your AOS hooked up?

AOS is disconnected from the intake an rerouted (via optional catch can) to the airbox through an opening under the filter. No more excessive vacuum under high load circumstances when going off the throttle. The AOS keeps in its �open� position. Under normal driving the airflow in the airbox creates enough underpressure to evacuate the crankcase gasses which are pushed out and filtered via the AOS.

Interesting what was the main reason you did this, what problems did the high vacuum give you??

The small puff right from start is only 1 out of 10 times. But the first 20 sec or so it sure smells fuely before the gray/ blue smoke takes over.

#Silk interesting inputs you are coming with. Injectors have been in my mind regarding the video. It’s from a day with less smoke than other days and it is hard to see the blue smoke in the video One or more oval cylinders is also in my mind, but my overall oil consumption is not that high? Engine is with Steel Liners and I don’t know if they known to go oval? I have tried to run 5w/40 instead of my normal 10/60 it was only short because then it overwhelmed the AOS and intake after hard driving? ( scavenger pump wear mayby??) but the startup smoke was mayby a little faster to clear up with 5/40 oil I hope to get some more time here during the winter to work on the car.

For those who have this smoking problem, do you drive the car aggressively before you park the car? If so, you can try driving it easy (higher gears less load) for the last few miles and see if that makes a difference.

I always drive home nice and slow through my villages and park the car in my garage. Doesn’t matter if I stop the engine imidiatly or let if idle a while. Smoke is the same. Also no difference if I drive auto or manuel with engine braking ( mine is a Tip tough)

Well, I wouldn�t run 10w60 oil, that�s for sure. Not saying that�s the problem, but I don�t believe it�s an approved oil for your car

10w/60 is much used en Europe and infact one of Germany’s best Porsche engine rebuilder Pomotec https://www.pomotec.de/ uses and recommends only Motul v300 Completion 15w/50 all year around

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Ok, but those weights are not approved by Porsche (that I know of). And, scientifically, 15w oil in extreme cold temps is almost certainly going to cause wear/damage via cold start. Viscosity is viscosity, no matter what people�s opinions are on the subject.

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Maybe he rebuilds more engines by recommending 15w?

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maybe the engine manufacturer does things to where the heavier weight oil is needed. Just a guess on my part.

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Haha. That�s evil!

Hartech also recommends running 10w50 when mileage starts increasing. In warmer climates it is certainly not a problem. Even less if you track your car. Even Mobil has a nice alternative with their 5w50 oil. Most of these higher viscosity oils also contain a bit different additive package. And don�t be fooled. The 300V double ester and equivalents do flow almost as good as the lower grades when cold. So at cold startup oil pressure build up and oil delivery to the engine internals is almost the same. So nothing to worry on the supply and wear side so much. The film formation and other characteristics however a different. Back on topic, my puff of smoke, did not go away when changing oil viscosities. I have tried a variety of oils from 0w40 or 5w40 in winter and 10w50 for summer and occasionally track day. Oil consumption of around 1 quart per 2000-2500 miles stayed the same over my previous 45k miles of ownership independent of oil viscosity used. Curious how it goes now all injectors have been cleaned and checked.

^^ Agree, except 300v looks about the same viscosity as 15w. It�s the viscosity rating at cold temps that matters (for cold starts). For example: � Mobil 1 0w-40 ○ Viscosity at 40C = 70.8 ○ Viscosity at 100C = 12.9 ○ Viscosity Index = 186 ○ Flash point 226C ○ Density = 0.8456 ○ Pour Point = -54C � Mobil 1 15w-50 ○ Viscosity at 40C = 125 ○ Viscosity at 100C = 18 ○ Viscosity Index = 160 ○ Flash point 232C ○ Density = 0.87 ○ Pour Point = -39C � Mobil 1 5w-50 ○ Viscosity at 40C = 104.3 ○ Viscosity at 100C = 17.1 ○ Viscosity Index = 179 ○ Flash point 232C ○ Density = 0.8499 ○ Pour Point = -42C Notice that viscosity at 40C for 0w is 71 versus 125 for 15w Mobil 1 vs Mobil 1. This 15w oil won�t even pour if it�s -38F outside! What is 300v 40C viscosity? About the same as Mobil 15w: Viscosity grade: SAE J 300 / SAE15W-50 Density at 20�C (59�F): ASTM D1298 / 0.868 Viscosity at 40�C (104�F): ASTM D445 / 122.9 mm�/s Viscosity at 100�C (212�F): ASTM D445 / 18.1 mm�/s HTHS viscosity at 150�C (302�F): ASTM D4741 / 5.3 mPa.s Viscosity index: ASTM D2270 / 164 Pour point: ASTM D97 -39�C / -38.2�F Flash point: ASTM D92 238�C / 460.4�F TBN: ASTM D2896 / 8.25 mg KOH/g All this said, it probably has almost nothing to do with smoke at cold start, Lol!

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The advantages are 1. no more degrading diaphragm in the AOS; constantly changing high vacuum, especially in high rpm coming of the throttle is what wears out the flexible diaphragm over time. 2. no more more oil and other dirt directly in the intake. 3. no risk for hydrolocking your engine in case too much oil gets past a not proper functioning AOS. Or in case the AOS gets overwhelmed by oil collecting in one of the heads for whatever reason. By rerouting the AOS it stays always open and functions as a normal catch tank, one with a oil retour to the oil pan. 4. cooler air in the intake, rerouting makes the crankcase fumes cool down more before they enter the engine again. makes for some noticeable extra bhp. The biggest advantage is nr. 3 Protect your engine. At least It saved mine two months ago when the scavenge pump in cilinder head 1 started deteriorating. At some point oil was coming out not only at high speed right hand turns, but even at 30-40mph. As the AOS vent in head 1 got overwhelmed with oil, pressure went up in the crankcase and oil was literally pushed out of the AOS. If that would have gone directly in the intake it was game over. At some point with a fast right hand curve 150ml got dumped out of the engine via the AOS.

Oli use the past 1500km is 0,5l but still the same smoke out of bank 2 exhaust. Clearing up after a few hundreds of meters driving. As long as I don’t let it idle. Changed spark plugs the other day and they are all quite black. Dry carbon not oily. Mostly cyl 3, 5, and 6 Maybe running a little rich? checked MAF but is looks fine and clean. Had a camera in all cylinders but dit not find any nasty things.