My AOS Madness..Ideas??

Hello everyone, Instead of clogging up the “what did you do today…” thread with this issue, I figured it would be best to start a dedicated thread on this. My new to me ’07 Cayman Base showed signs of a failed AOS. Smoke on startup from oil in the upper vent hose and throughout the intake. I have replaced the AOS twice and replaced the upper vent hose (AOS to intake Plenum). Each time I have cleaned up the oil in the plenum, intake and crossover tube. Sadly, I am still getting oil into the vent tube on the Driver side only. The passenger side is dry. I have taken my car to a Porsche shop, and they were quite stumped as to what is going on. They performed a compression test, vacuum test and bore scoped the cylinders. All tests came back great, no issues found. So here I am with a great running car that used no oil on a 1,300 mile road trip I took recently. This is really the only issue I have with it and is rather embarrassing to blow out a cloud of oil smoke on startup. Usually happens in the morning on a cold start and after the car has sat for several hours. Most of the time it takes about 15-20 seconds to clear up. Other times I get nothing or just a puff. Ideas anyone? Someone local to me suggested another shop that is more dedicated to the water cooled cars. The shop I went to is well respected in town, but they seem to cater more to the air cooled cars. This is something to do with the AOS and intake. I’m not sure if oil is being sucked up through the AOS or if something is causing oil to be pushed up through the AOS and into the vent hose. My oil level is in the middle of the gauge on level ground. First picture oil coating the plenum, which is all over the intake. Second picture is oil at the top vent of the AOS. Third picture is oil in the plenum where the drivers side vent hose attaches. I'm hoping someone has an idea or two for me to look at before I schedule an expensive visit to another shop. Thanks!

Hey there, as per my prior post, I have been facing a similar issue, for the past 3 years, with my 2000 C4, after replacing the AOS, I still was getting smoke and oil usage, but, only when I’m on the track.. no smoke or oil usage during normal daily driving. After doIng suspension upgrades and moving to R compound tires over the winter, my first time on track this season I had a lot of smoke, was going through 600ml of oil per 20 minute run group and ended up with a small puddle of oil under the car. In the past few weeks we have now put in another AOS and will be looking to try it all again in a couple weeks when I return to the track. I tried to go to the Performance AOS but it only fits on 2003 cars and newer. If you hear of anything that addresses the issue, please do post your findings.. I will also do the same. Thanks for the post. Have a great day.

pdxfj- I am guessing here, but I recall another member a couple of years ago blowing out an oil plug in his head due to internal pressure. Seems that somehow the head oil return had something blocking it, so the head oil found the vent tube to the AOS and also pushed out his oil plug. Luckily he smelled oil smoke before the engine expelled enough oil to explode. To you case, I suspect that oil is being pushed up the vent tube on the drivers side. A catch can on that side would confirm this. Maybe fashion something from your old vent tube that you recently replaced. If you get a bunch of oil in the catch can, then you have a blockage in the oil return passageway to the swirl pot then to the oil pan. Not sure what this could be blocking that passageway, maybe part of your chain tensioner or something else. You can check this by removing the vent tube at the head with the engine going to see if you have oil moving up the vent tube. I am no Porsche expert, but I am interested in this due to a recent AOS oil bath. I changed my oil pan to an LN deep sump system with 997 down tubes in place of 996 swirl pots. LN says these 997 down tubes enable more return oil flowing from the heads, which is very important in high g corners as there are two head oil pumps to remove the oil, but one maybe weak. So, any issues you uncover may be important for me to know in the future. These are very expensive engines.

When I changed the upper vent hose I took the AOS out, I didn't remove the vent hose from the front of the drivers side head but I did blow into it and could feel air coming out of the block where the AOS mounts. I did some more searching and came across this thread which is rather interesting. While it's for a 986 and I'm not experiencing all of the same issues, I feel some of it might actually apply since a number of the symptoms are the same. oil cloud when running hard - 986 Forum - for Porsche Boxster & Cayman Owners

Occam's razor, check for an overfilled sump. If it were me I would drain the oil including filter housing and meause what is in the engine. Really cheap item to rule out. The dash oil level gauge in my car is moody on a good day and I don't trust it. Sent from my VS995 using Tapatalk

My bet is a weak or defective oil return pump on the drivers side head allowing oil to accumulate in the head and be pushed up the vent tube into the aos. My guess at this point. Its worth the money to replace the pump as racers have had oil starvation do to oil collecting in the heads on long high G left hand corners. The #6 bearing usually goes bad from scarring, lack of oil allowing metal to metal contact and heat. If you can do the work yourself, then buy one pump for the drivers side and give it a go.

Yeah... I've been mulling over the same idea for a bit now. Not really sure what else it could be. Thankfully they are not too expensive and there is a fair amount of room to reach the drivers side one.

Well.. I spoke too soon on the expensive bit.. turns out the drivers side scavenge pump is a "tandem pump", which is both an oil pump and a vacuum pump in one. That drives the cost up to the $400+ range.. soooo.. it'll have to wait for now.. As far as oil level, I already tried that.. no difference.. I'm not tracking car and I've done one AX day in it on street tires.. doubt I'm fast enough in AX to cause issues.. Car is just a driver at this point and a very fun one at that. When I do change the pump, I'll post an update.

Just a quick update. I decided I was tired of laying under the car and had the shop that did the initial look over, replace both pumps while I was out of town for a few days. Their labor charge was very reasonable. Cleaned out the upper vent hose, plenum and intake again. Took the car for a bit of drive on Saturday and gave it a good flogging. So far no smoke on startup, but still need some more miles. I will make it my DD this week and pull the engine cover again this weekend to see how things look. I am interested in doing the 1/2 quart deep sump and the 997 down tubes. Something to think about this winter. Would you have the part number handy for the 997 bits?

Both LN and Mantis make deep sumps with windage trays. LN has the 997 down tubes included in their kit. Others on this site suggest using 996 swirl pots, so I called LN to find out why they recommend the 997 as these do not have the swirl mechanism, just a straight tube. Their response was the need to get the oil from the heads as quickly and efficiently as possible and let the windage tray slowly release the air bubbles in the oil before dropping into the oil sump below. I found that this works, but it also puts more pressure on the OEM AOS as a lot of this oil is now closer to the AOS than before ridding on top of the windage tray going up the side walls durning high G cornering and into the AOS vent hole. If you are not using R rated tires, this is a non issue as the oil does not ride up the side walls as much with regular tires. My fix was to install the Porsche MotorSports AOS, which is more effective and quite a bit more money than the 996 AOS without water heating, which will work with modifications to the engine compartment. A side note about the LN deep sump oil pan is, the oil temp will be less in track use as reported by a couple of 987.2 owners and 1 987.1 owner. I would imagine that the Mantis sump would act as an oil cooler as well. Both of these most likely do not work nearly as well as a dedicated front oil radiator. There is one additional oil cooler/water interchanger that can be modified to a more effective 3.8 version.

So another long overdue update... Been doing quite a bit of travel for work and haven't had much time to fiddle with the car. Started getting smoke on every startup. It is consistently the same amount every time. Decided to do a few things. First of all I took everything apart again to check for oil in the intake. None to be found. Good to see it was still clean from the last time I took it apart. Plenum and upper vent hose were dry (YAY!). Next I removed the lower vent hose to check and clean it. Found a crack in it, which is not surprising since it was quite brittle. Ordered a replacement and installed it. Not fun getting it off the drivers side, even with my long skinny fingers. Thought maybe the oil I used was not playing nice with the car do decided to replace it after only 500 miles. Upon removing the drain plug (after the car had been sitting for several days) I was greeted with oil that was more like water and reeked of fuel. Ordered a Blackstone kit to confirm my suspicions. So now it's looking like I have an injector (or multiple) that is not closing all the way after I shut the car off and dripping fuel into the intake. Found replacements for not much more than it costs to have them professionally cleaned, so just going to order a brand new set. More to come as I continue my rather endless quest to stop my Cayman 's smoking problem.... Hopefully no scoring issues from the excess fuel in the cylinders... Here's a video I found of what might be going on with my injectors... https://www.youtube.com/watch?v=Y2l0L8B4J-g

Check your spark plugs for raw gas, maybe you can isolate one injector or just install the new ones. I don't want to set off the alarm bells, but after the injector is done, run you car for another 1000 miles then change the oil again, just to make sure all is well. If you are still smoking, well find an heavier weight oil, like Castrol 5W50 with ZDDP and start down shifting a lot. I read that downshifting throws a lot of cooling oil on the hot cylinder walls. If you can get to 1 or 2 qtrs between oil changes, then I would call it good. Maybe you will find the blue smoke on start up getting less noticable week to week.

I have thought about pulling the plugs to see if I can isolate which cylinder is leaking. I pulled the engine cover last night to see how bad it will be swapping the injectors and the passengers side doesn't look too bad. Looks like I will have to pull the air box for the drivers side since there is not enough room to get the fuel rail out. Have been running Castrol Edge 5w-40 and do plan on changing the oil again after swapping injectors and running the car for a while. If it's only one injector on the passengers side that is leaking, perhaps I'll just change that one.. if it's on the drivers side, might as well do them all since it is a lot more work to get at them. Can say this is one situation where working on my 944 is easier.

Just a quick update. Pulled spark plugs this weekend and found #1 was the culprit. Plug had a sheen to it and I was able to wipe the carbon off with my finger. Top of the piston looked like it was a sticky, wet mess. Replacement injector and o-rings for the other two are ordered. Hopefully by the end of the weekend, I will no longer have a Cayman with a smoking problem.

If you have solved the fuel injector problem, change the oil again. Then run the car hard for an hour or so and see if you have any smoke the next morning. I would have at least 5 minutes of good cool down period to get a lot of oil around the bottom of your cylinder's walls by downshifting during the cool down period. That raw fuel did not do that 1 cylinder's wall any good, so build up your intensity slowly, then cool it down slowly. Your engine problem are certainly not the normal issues, blowing up the AOS a couple of times then finding a head oil return pump defective. After that issue, then finding a clogged fuel injector that contaminated your oil with gas, man that's just bad luck. Who owned the car before you, a little old lady. These cars are meant to be driven and sometimes hard to keep all the parts working correctly.

Hey pdxfj, I don't have much to add to this other than I just stumbled upon it and have the same problem. My '07 2.7 Cayman 5-speed has 178,000 miles and I drive it every day, summer/winter in the north country. I am getting very intermittent but sometimes good sized puffs at start-up. For a time, I thought it could be associated with parking angle (my driveway is not level). When it began happening on perfectly level ground, both in the morning and/or after work but still intermittently, I replaced my AOS. My original was full of ugly tan/brown sludge but the diaphragm did not appear to be cracked or damaged. The problem has not gone away. I did not throughly clean my intake and drains and am a little embarrassed to admit that I didn't study and know exactly the function of each port and line in the AOS system (I broke the brittle corrugated plastic tubing attached to the AOS) I have many start-ups with no smoke but then, as you mentioned, I will cloud my level, workplace parking lot. Remarkably, this car has never used a drop of oil between 9,000 oil changes with Castrol Edge 5w40. I cut my filters open and they have gotten cleaner over time. At 178k, can you tell me if this sounds like AOS and breather-side problems or could it be something worse? Sorry for the lengthly reply.. Thanks, C

Crispy-Try Chevron fuel injector cleaner. As Pdxfj found a leaky fuel injector that contaminated his oil. Run that additive through about 5 tank fulls of gas. If there is some carbon or other material that is preventing full closure of the injector after shut off, the fuel in the rail will drain into that cylinder. During the combustion stroke, the piston will try to compress the gas, which is non compressible and will force the excess fuel that does not fit in the top of the head down the side walls past the rings into your sump. Over time, the boiling point of fuel is very low, so it will evaporate. The down side is the gas will go into your sump, and be used for lubercation until its evaporated. As Pdxfj found that one spark plug has gas residue and on the piston as well, so you may want to change your spark plugs to find the problem injector. Your smoke could also be from oil that somehow has bypassed the AOS. The oil does not hurt the motor on startup, its just an embarsement for you, unlike the fuel injector issue which could lead to a lot of fuel contamination in your sump. Lastly, the smoke on start up could be early signs of bore scoring. No oil use is a good way to check off this box, with no oil added for 9000 miles between changes? Bore Scoring is an issue due to not warming up your engine before starting out, then using too much throttle, causing the piston to expand while the cylinder walls are contracted by a much lower temperature. Also from too much throttle below 2000 rpm. Down shifting is a good way to help lubercate the sidewall of cylinders, especially after running the car hard.

Finally had some free time to fiddle with the injector. Thankfully it was #1 and I was able to get at it from the front of the motor. Any other injector and I would have had to take the intake manifold off on that side. Took about 90 minutes and no fuel leaks on startup. Ran the car for about ten minutes last night to check for leaks and allow everything to clear out. Went out again this morning and NO SMOKE on startup. I have not driven it yet since I need to put the engine covers back on, but will take it for a short drive after work and will drive it to work tomorrow. There are only a couple of starts on the fresh oil in the engine so I'm not super concerned about the amount of fuel in it, but will change it this weekend. Still keeping my fingers crossed, but it looks like I may have finally reached the end of the madness.

Persistence pay off. Great going to finish the job.

good job on the detective work

Well... don't pat me on the back yet... Car is still smoking on startup. Drove it to work one day last week after changing the fuel injector, started it the next morning and was greeted with the same cloud. The amount of smoke is the same each time. Ordered a small inspection camera that will fit into spark plug holes. Since I'm not traveling for work this weekend I will have time to fiddle with the car. My plan is to take it for a drive on Saturday, park it and pull the plugs on Sunday and see what is going on. Guessing #1 is still wet and I'm hoping to see what color the liquid is. It doesn't smoke after short drives, only after being fully warmed up. Might be a head gasket at this point?!?!?!?!?!?!? Talked to the local indy shop I've gone to a few times and even they are bummed over all of this. If it is a head gasket, lets hope it is only that and not something more serious. Would really suck to have a cracked cylinder or cylinder head... I do have video of numerous start ups showing the amount of smoke. I will try and toss together a video of that and what I see in the cylinders this weekend. Bit bummed over all of this, but it is the Cayman I always wanted and if I need to buy a used engine, I will. Would consider the water cooled LN Nickies route if the total cost isn't a massive amount over a good, used engine. Stay tuned....

Thanks pdxfj for the update, I still don't have much for you except we might be in the same boat. Reminder- I have a 2007, 2.7 5 speed Cayman with 179k miles. I drive it every day. A month after replacing my AOS, my car still smokes on startup. Some times it doesn't and there is no clear pattern. Sometimes the cloud is bigger and sometimes it's smaller. The one thing that bothered me about my original AOS is that it didn't appear damaged. It was nasty inside and had some coffee colored **** in it but the diaphragm looked functional. My car never smoked or used a drop of oil between 9k mile changes. Haven't had the plugs out since a plug and coil pack change at 97k miles. I'll add anything relevant I can. Thanks, C

Ok, same amount of smoke on start up, but is there gas in the oil. If not then you can still use your car by checking the amount of oil in the sump on startup. Even with a small amount of blue smoke on startup, you can keep track of oil usage. Also you may want to do a pressure test on the cooling system to see if combustion gases are leaking into the system from a cracked head or leaky head gasket.

My weekend didn't go as planned. Saturday was eaten up by other things and I managed to get some funky 24 hour bug on Sunday which wiped me out. Did get out in the garage last night after work and use my new inspection camera. Started off with looking at the intake valves for possible leaky valve seals. Didn't see anything that stuck out, but the lower side of the intake is filthy. I had to keep pulling the camera out and wiping thick, black oily crud off it. Almost like dirty, old grease. Upper AOS vent hose is clear, with a smidge of oil build up on the flat part of the plenum (around the valve). There is a faint fuel smell to the oil. Coolant is clean and smells like antifreeze. I have not changed the oil yet. Want to check as much as I can before doing that given the cost involved. Pulled plugs on #1 and #2. #1 plug looks normal and dry. Carbon buildup is only covering the top half of the piston. #2 looks fine as well, with what looks like an even covering of carbon across the entire piston. Was out of energy by that point. Feeling much better today so I will go out again this evening and finish looking at the rest of the plugs and cylinders. I do not have the proper adapters for my cooling system pressure tester to fit the Cayman . If I do not see anything that stands out, I will take it back to the shop and have them diagnose things further and also ask for a pressure test on the cooling system. Guessing at the very least, the intake manifolds need to be removed and thoroughly cleaned. They did mention pulling the pan and having a look at the cylinders from the back side, thus another reason I haven't changed the oil yet. Nice to see I'm not the only one having this issue, but frustrating not to find the cause of it.

A bit more information: When I first looked at the plugs to determine if any injectors were leaking, I didn't look at #4 since it's a pain to get at. My thought was only pull it if I didn't find anything else. So, when I pulled #4 last night I saw the same sheen on the plug as I originally saw in #1, just not as bad. All other plugs looked normal, including #1. It would appear I have two leaking fuel injectors. Given they are both at the head of the fuel rail and with 100k on the clock, I'm not too surprised. It was a toss up as to which pistons were clean and which had a coating of carbon on them. Something does not feel quite right fuel wise to me. My thought process says I should remove the intake manifolds and give them a deep cleaning since they both have a large buildup of oily, greasy curd in them. While the manifolds are off, I might as well replace the other five injectors. I could send them off to get cleaned and flow tested, but there is not a huge cost difference vs. new. The one I replaced was only $40 for OE Bosch. Going to buzz by the shop on Friday morning and talk with them about what I found. They suggested pulling the pan and inspecting the back side of the cylinders which I'm ok with, if they still want to go that route. At the very least I will have them remove and clean the manifolds and replace the other five injectors. While I am totally capable of doing the work, I really don't feel like it at this point. Also have them do a pressure test on the cooling system just to be safe. Yes I will do an oil change after everything is done.

pdxfj- I have not heard from you regarding any additional injector problems? I did find a additional solution to help clean those dirty injectors. p.i. performance improvement by Amsoil. Look it up, seems like a reasonable additive. Do you think this residue and leaking injectors was caused by bad gas over the years? Just trying to get a sense of why this happened to your car and not to mine. What can I do to prevent this in the future?