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sudden oil leak from Cylinder head

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Having a problem with sudden massive oil loss on my 01 996 C2 (86k original miles) .  Here some of the background. it is ca. 900miles since IMS/RMS replacement. Perfectly runing car, no codes, no leaks. Since I am new to 911, I was wondering about oil consuption  - which was ca. 2 quarts (I thought my  Cayenne CTTS consumes plenty of oil (>1Qt/1K is normal)) , but to my surprize, from discussions with local fellows with air cooled 911's  , I can expect a quart / gas tank on a carrera engine ) . So I thought a quart /  450 miles  (about two tanks) is not unusual. I also noticed no leaks under the car at any time. What I was concerned , however, was about the recommendation to use the M1 5W-40 diesel truck oil (Which I used since the IMS/RMS work). Reading through misc oil threads, I ended up w/o a clear direction (except to do it 5k or less intervals) , and decided to try what Porsche recommends - and this is 10W-40 for the climate I am in - with 50-60F. So, I swapped the M1 5W-40 dt oil after less than 1k miles for M1 10W40 high mileage oil. The dip stick showed max./ the dashboard gauge was in middle . The car ran perfectly fine for ca. 50 miles (a  day commute to office). This afternoon I drove the car slowly for about 10 min (just to local store a few miles away)  and once back home I parked the car curbside for about an hour. Then , while parking the car backwards on driveway ,  to my surprise I saw a major oil puddle  of ca. 4 sft caught my attention just below where the engine was sittiong above the last hour. Double-checking driveway shows not the slightest signs that this could have started before I started the car today less than an hour ago.  Backing up the  car onto  garage (engine does no unusueal sounds while doing so ) , and checking oil-level. The dashboard shows 2 bars above min (which is about one less since I filled up last).  Dipstick, however, shows barely above min. Checking the floor, I see the oil dropping from rear cross bar. Jacked the car rear  up and identified that all is perfectly dry around Trans Bell-housing (my first concern, but it confirms to me RMS/IMSB area is not guilty here). However, there was oil deposits on LHS Drive Shaft, car underbody above  , and all in the plane in line with left cylinder head gasket . I wiped the head gsket area dry, but which shortly after leaked oil again @ lowest point of left cylinder head (engine off....).   I am confident by now is that no mix of coolant in  oil or vice versa. What I am puzzled about is that all seems to have started since I switched to the thicker Oil at lower temp two days ago.  My question is whether the situation is more or less known / whether I can still diagnose / fix leak from "outside" , or do I need to drop the engine and start tearing the engine down? 

Screen Shot 2017-02-27 at 1.55.48 AM.png

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I think it would be the best if you can check with the shop and see if you should tow it to them to take a look.


Also you mentioned head gasket, did you really mean that or you meant the cam cover gasket? Note there's no cam cover gasket. The cam cover to head surface is sealed by sealant.

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2 hours ago, Ahsai said:



Also you mentioned head gasket, did you really mean that or you meant the cam cover gasket? Note there's no cam cover gasket. The cam cover to head surface is sealed by sealant.

yes, i mean the gasket - not the split casing of the cam cover . i pointed to the interface where the main oil spill emantes with red arrows in the picture of my original post. 

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20 minutes ago, Ahsai said:

I see now. It's unlikely the leak is from the head gasket though. I suspect it's from the AOS or its hoses then.

if the aos or hoses are right above  i could imagine to have capillarity force oil down along the gasket interface and may appear leaking itself. i hope it is the case. will try to get more light into this with an inspection camera. just in case the aos needs replaced- do i have to remove the engine - or has this been done before while in car?

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1 hour ago, Ahsai said:

Some pic of aos leak here http://rennlist.com/forums/996-forum/594986-oil-leak-driver-s-side-not-rms.html


Another potential source is the variocam solenoid seal but that should create more stain on the valve cover.

thanks folks for the advice so far. attaching picture of the aos from view under the car. i realize the very oily connector is farther away from gasket plane than assumed before seen. also visible is that the aos features only a (very)light vertical stain of oil, and the visible hoses and connections seem dry. working now myself to aos from the engine bay side ( the pelican way ). hope this gives more insights on the source of the leak. 


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root cause found! the aos dome is severely  cracked over at least 1 inch along the perimeter, cose to the small tube soigot. container is breathing oil towards the lhs of the engine.  i finally discovered it by profiling the the dome cover by finger from the bottom of the car. then i tried to take a decent snapshoot- sharing below.  glad to get to this point before leaving for a b-trip for the week late tomorrow. will be just in time to receive the new aos for completion of the replacement on during WE. 

thank you all once more for your constructive hints. 


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sorry. i just realized the typo in the thread.  i mentioned 02 in the footer though. yes it's certainly a 3.6l. however, you maybe right- while digging in the car i have found misc signs that the engine may have been out for some service  during the car's life (eg some difficult to reach plastic tubing is date stamped 2003...). but having had the car for 2 months now, and having adressed three of the major m96 issues diy ( ims,rms, aos), i realized how well this car is designed - to be easily taken apart, and that engine removal ( which would likely save a lot of time i spent), now looks much easier than i could imagine . it is the first car i really enjoy to work on.

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52 minutes ago, Ahsai said:


You said you have already addressed the AOS. Does that mean the new AOS is leaking?

no. the leaking one is the one which was in the car . i only consider this problem already as remedied - from the moment on , when i identified the mechanically broken ( fractured) plastic part . heat cycles and dry west coast climate were obviosly not considered enough when material choices were made. these cheap things brought my cayennes down multiple times  with the last ten years i owned one, and seeing this here on the 966 ( and much better accessible) looks so much easier to call it done...

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20 minutes ago, Ahsai said:

Ah i c. You may feel differently once you start tearing into the AOS. It's anything but accessible :)

well, i had to stop at the coolant reservior removal as my 3/8th inch drive was not strong enough to loosen the two engine mounting bolts to lower it slightly.... short of a 1/2 in drive, but i believe i am already far.... at the same time i already removed tge front screw holding aos. the rear may be accessible as well ... thinking of removing the alternator will give me better access . i am just curious... if a no-go working i will finish it the pelican way this we. 

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just a little update after I did the the re-assembly of the car today. My conclusion is - never again w/o taking the engine out !  The "pelican-way" is what worked for me overall. However, it possibly took way too much time (a full day... ),  and  I almost through, I figured that that small extra feature on my new AOS made it basically impossible the install the rear manifold screw the way I removed it (via 10 mm socket). The feature was literally above the screw-head (See the inspection camera view). I am not sure whether this feature is normal on all new AOS, but possibly I should not have chosen the aftermarket AOS. However, since Pelican sells both , I'd like to share how this minor issue was fixed w/o tearing all apart again. All I needed was a ~4 in long 10mm ring-wrench (I just broke one I had in two pieces). Getting the wrench between the AOS and screw was still difficult, but after rotating the screw-head a couple of turns by hand, I could get the wrench in place, and patiently rotated the screw until the manifold was proper held in place. OK. all connections are in place, no screws are left over, and all fluids at proper level...:). in the morning I hope the first startup & post will go smoothly .  






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  • 2 weeks later...

" All I needed was a ~4 in long 10mm ring-wrench "

Thank you for taking the time to show us what special tool worked. The Pelican kit should include such a peculiar wrench - then there would be a really useful "Pelican way" ! The correct terminology may be a "Stubby" 10mm wrench -Mac Tools have one : MXS102KS

Edited by Schnell Gelb
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