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Pelican Technical Article:

911 Oil Leak Fixes

Mark Jo


3-4 hours






Metric socket and metric wrench set, Phillips head and flathead screwdrivers, shop rags

Applicable Models:

Porsche 911 (1965-89)
Porsche 930 Turbo (1976-89)

Parts Required:

Oil breather cover gasket, oil thermostat O-ring, engine oil cooler O-rings (3 of them)

Performance Gain:

No more oil leaks

Complementary Modification:

Replace oil and oil filter
Figure 1
Figure 2
Figure 3
Figure 4
Figure 5
Oil Leak Fixes
  • Oil Thermostat
  • Oil Breather Cover
  • Oil Cooler (Engine)

     This article reviews a couple oil leak fixes that are common areas of leakage for older Porsches. The car used for this is a 1982 911SC. Techniques may vary from model year to year.

     Also these are repairs that are done with the engine out of the car. I did these while doing a clutch repair. I have heard that the oil thermostat and the oil breather cover can be done with the engine in the car but necessitates the removal of the entire CIS system. The oil cooler involves either a full or partial engine drop. Partial and full engine drops can be found at the technical article section.

     With the engine out of the car looking at the flywheel end of the engine we can proceed. In (Figure 1) you can see the 3 points of attack labeled.

Oil Breather Cover

     If your engine was anything like mine there should be a puddle of oil here around the breather cover. If not this may not be an area of leakage, but it is a common one. If you look carefully (Figure 2) there is a sensor with an electrical connection coming out of the cover. Unplug the electrical wire at the end of it, and screw it out. Then there is a bracket connecting your accelerator linkage to the air box. Be careful taking this off because if the rubber of the air box is old it will snap off (like it did for me) but can be repaired with epoxy. It does not look like it is vital, just a support bracket. After that you must go ahead and remove the whole accelerator linkage plate to be able to get your wrenches at the oil breather cover nuts. From here it may differ from engine to engine.

     A Pelican BBS member said that for his Carrera 3.0 he had to remove the whole CIS system, but on my car I was able to do it with a little bit of cheating. You can see that even with all the nuts loosened and removed, the breather cover cannot be lifted because of the pipes above it. And with some careful observation you can figure out which clamps have to be loosened so that the pipe system and the round gold modules (Vacuum modules?) can be removed as a unit (Figure 3, Figure 4). Hose clamps have to be undone at the junction directly above the oil breather cover then at the multi junctions above the oil thermostat, and also over on the side of the engine.

     When all the hose clamps that need to be loosened are, and the 2 support brackets holding up this network of tubing are undone, the tubes can be pulled off. But even with this, the breather cover still does not have the clearance to be lifted clear of its studs. So to solve this, I undid the intake manifold nuts on the 2 most flywheel side cylinders (Figure 4). And I was able to tilt the intake system enough to remove the breather cover. With the breather cover off, put it on a level surface like a piece of glass to check for warpage or unevenness. If so you can place a piece of sandpaper under it, still on the piece of glass and sand lightly to level it. If it is bad, you will have to purchase a new one or have a machine shop level it for you.

     The gasket for the cover was purchased at The one I pulled out was cracked in several places leading to the oil leaks. To prepare my gasket I coated with a light coat of motor oil, but I have heard different opinions. Some say install dry, and other use a Loctite gasket sealer. If I were doing this again I would probably use the Loctite, but my oil-coated gasket seems to be holding up. Installation is reverse of removal. But do not put all the parts together yet.

Oil Thermostat

     To the right of the breather cover is the oil thermostat. It looks like a circle with 2 tabs for the nuts holding it in place (Figure 2). Directly in front of it is the oil pressure sensor that needs to be removed. Then the removal of the Oil thermostat is straightforward. Undo the nuts and lift it straight up. If the thermostat comes out easily, that means the o-ring is worn and is no longer sealing. But even so changing this o-ring is cheap insurance when the engine is exposed. Roll off the o-ring, coat the new one with a coat of motor oil, and slide the thermostat back in. You should feel some resistance indicating a properly sized and sealing o-ring.

Engine Oil Cooler

     To tackle the engine oil cooler o-rings we have to be able to support the engine, and remove the passenger side heat exchanger. If you engine is on a stand, no problem, but I worked on the ground by supporting my engine on the driver's side and the middle of the crankcase. You should also put some support under the passenger side heat exchanger to be safe. For information on heat exchager removal see the tech article on heat exchanger backdating at Once the heat exchanger is removed securely support the engine from both the sides and middle. The lower 2 oil cooler nuts should be exposed. Also take off the white-ish oil cooler shroud on top of the oil cooler (Figure 1). This should expose the two upper oil cooler nuts. Put a turkey roasting pan under the cooler because there will be a lot of residual oil in there. Once the cooler is off you will be able to see the 3 o-rings. Two are the same size the other is different (Figure 5). These o-rings can be purchased at Coat these rings with motor oil and install.

     Now you can reinstall everything and you should have solved 3 major areas of oil leaks. If leaks persist, clean off you engine bottom with a degreaser or brake cleaners and then you can better track down the source of the leaks. Other common areas are any junctions between oil line, or the oil line and the crankcase. Also culprits are the oil return tubes that can be replaced using the tech article available at

Comments and Suggestions:
boscoo1 james Comments: I have a 1986 911 3.2 non turbo that has oil coming from the exaust in excessive amounts.It appears that the sump pump is not pumping the oil back to the tank and the oil is pooling in the block.How can I test the sump pump?
October 11, 2017
  Followup from the Pelican Staff: You can check pressure and volume on the return hose to the tank from the sump. - Nick at Pelican Parts  
ruel Comments: i have a 1989 porsche 911 c4 with 78k miles...that i had spent 5k last year to fix major oil leaks.. i was told that another 5k should stop it altogether ...i live in roseville, ca..any recommendation for another mechanic in my area?
May 8, 2017
  Followup from the Pelican Staff: Only two Porsche shops I know well enough to recommend are Callas Rennsport in Torrance and Schnieder Autohaus in Santa Barbara. - Nick at Pelican Parts  
JDC911 Comments: Has anybody tried to change the right side oil lines on a turbo body 85 911 that has rear brake vents that block access to where they connect to the thermostat?
July 24, 2015
  Followup from the Pelican Staff: I recall the ducting has to come out, but it has been a while.

I opened a post in our forums. A Pelican community member may be able to answer your question.
- Nick at Pelican Parts
Byron Comments: bottom engine oil leak from sump studs. Replaced all with Pelican kit. Cleaned and inspected, found a small horizontal notch about 1/4" wide IN THE BLOCK above the oil cooler; can see the edge of a black vertical tube magnetizedembedded in the notch inside the engine, with oil seeping between it and aluminum block. Seeps down to sump and drips from there. NO mention of the notch in Wayne's book or anywhere else. 1978 911SC I am baffled
February 9, 2015
  Followup from the Pelican Staff: I can't quite visualize it. Is the oil leaking down in between the cylinders and the oil cooler, or between the engine tin and oil cooler? A photo of the oil leak from the bottom might help me get the whole picture. Or if accessible a photo of the notch in question. I remember seeing some epoxy repairs on cases in the area of the oil cooler. - Casey at Pelican Parts  
Tom Comments: I can't find the source of my leak looks like behind the engine, had thermostat resealed about a year ago, but lately started dripping a lot, like I have a stripe following me down the road with drops about every foot or so depending on how fast I'm going, any suggestions what could be leaking that much? thanks
December 29, 2014
  Followup from the Pelican Staff: What fluid is leaking? What is the vehicle model and year? - Nick at Pelican Parts  
Tom r Comments: 95 993 C2 with 70,000 miles: I smell heated/hot oil after a 20 minute drive - that smell you get when you spill oil on a hot engine... I have not observed any oil leaks under car, nor after she sits for a bit. Any ideas on where to start looking?
September 21, 2014
  Followup from the Pelican Staff: Valve covers. Check there first. - Nick at Pelican Parts  
Walter Comments: Good morning. I am working on resolving an oil leak from the oil thermostat on my 1970 911T. I purchased a replacement O-ring and, to my surprise, upon removing the thermostat discovered that the existing thermostat did not have an O-ring. In the place of the groove for the O-ring that I see in photos is a metal band/seal that is not removable at least not easily. Are you familiar with O-ring-less thermostats and is there any solution to resolving it leaking other than buying a new thermostat that accepts an O-ring?
April 21, 2014
  Followup from the Pelican Staff: I believe you should be able to get a sealing kit, if not, replacing the thermostat might be the only option. Give our parts specialists a call at 1-888-280-7799 and they can help figure out which part or repair kit you need.
- Nick at Pelican Parts
Daniel Comments: I have recently have repaired my 964 car engine, change piston rings, seals etc, the mechanic accidentaly overfilled with oil the engine and when I turn it on smokes a lot, what should I do?
Thank you
January 5, 2014
  Followup from the Pelican Staff: Put the correct amount of oil in the engine. Then clean the throttle housing and intake manifold, as there will likely be oil residue. This should clear up the smoke. - Nick at Pelican Parts  
Paul Comments: I have an 01 911 carrera, there is now oil mixing with the coolant, but cannot find any coolant in with the oil. could this be the oil heat exchanger? If so how do I test it after removal?
October 2, 2013
  Followup from the Pelican Staff: Once removed, you could seal one side of the coolant passages with a cap, then pressure test at the other passage. - Nick at Pelican Parts  
Enzo777enzo Comments: Hello i have big leak, when the car is in Garage. I check And it comes from right side near gear box. But i not sure, what the problem. Car is targa 1972. I think is from From 2 tubes in motor with exagon nut. This tube are down of oil raditor, more ore less. Before car leAks i try to tight this nut And do little sound, And i stop. I think maybe i broke something. Can you help me?.? Regares
September 29, 2013
  Followup from the Pelican Staff: These are oil lines. I would clean them off and inspect the area of the leak. Once you locate it, replace the parts that are leaking. When removing the large nut on the lines, be careful not to bend the pipe. - Nick at Pelican Parts  
Lori Comments: 1991 911 oil leek on the right rear
April 28, 2013
  Followup from the Pelican Staff: Check the valve covers. - Nick at Pelican Parts  
chilly Comments: 78 911sc, when rear hood is raised straight up leaks good amount of oil, porsche dealer could duplicate but couldnt give me a reason, two other mechanics were clueless also, any help would be great
March 4, 2013
  Followup from the Pelican Staff: It's possible the support arm of the hood is hitting or lifting a faulty oil line, causing it leak when the good is open. - Nick at Pelican Parts  
Dean Comments: Followup question..... In the 356 can the oil cooler be mounted remotely off the engine to eliminate the vibrations that the oil cooler impact into the case. I do have a method to do this but has it been done? It may take an extra fan to move cool air across the fan. Has anyone tried this? Or has it been tested?
March 1, 2012
  Followup from the Pelican Staff: There is a remote oil cooler available. I think most people go with a high flow instead. - Nick at Pelican Parts  
Dean Comments: I have a T5B 356 that now has a non leaking engine. But, I have another engine in my garage that has an oil leak in the case where the oil cooler mounts to the case. There used to be a shop in Southern Calif that fixed these crackes and the case groove that was manufactured in the case. Does any one know where this shop is now. I think it moved from Sourthern calif to cenryal calif.
March 1, 2012
  Followup from the Pelican Staff: I am not sure of the shop, but the crack can be repaired.

I opened a post in our forums. A Pelican community member may be able to answer your question.
- Nick at Pelican Parts
Joe Comments: REAR MAIN SEAL CHALLENGE - Have a 90' C4 35K miles converted by Protomotive to twin turbo by previous owner. Recently upgraded cylinder, heads, added a 993TT turbo oil scavenge pump, and other parts, case was also split so oil pump seals and other items could be freshened up. Your book heavily referenced. Engine back together but RMS leaking bad. Dropped the motor and see the RMS was not fully seated, made sure all was hospital clean and seated a new RMS flush with the case. All back together and still seeing what looks like a RMS leak, but not as bad. Any non-obvious tips on RMS install? Chance I botched the install? Chance just a bad seal? If no visual nicks or damage on seal can it still be bad/ineffective? Willing to drop the motor again, don't want to do it a 3rd time. Chance my 993TT pump addition or other non-stock items are causing oil distribution issues that is forcing oil past the RMS?
November 9, 2011
  Followup from the Pelican Staff: When you drop the engine and remove the seal, check the seal seating surface on the crankshaft carefully. If there are grooves in it, that could be your problem. Also inspect the seam at the crankcase where the seal seats. - Nick at Pelican Parts  
Bill Comments: I have a 79 911 SC, the air pump is making noise, is it ok to remove the belt and not use the pump ?
November 6, 2011
  Followup from the Pelican Staff: If you don't have emission regulations it would be OK. Here in the US you are not allowed to do this. - Nick at Pelican Parts  
m88gta Comments: I HAVE A 70 911 T,, I THINK I NEED A Oil Line Hose, Rubber, Oil Tank to Cooler 'S' Hose] WHAT SHOULD I KNOW BEFORE TAKING THE OLD HOSE OFF? THANKS
October 14, 2011
  Followup from the Pelican Staff: Give our parts specialists a call at 1-888-280-7799 and they can help figure out which part or repair kit you need.
- Nick at Pelican Parts
T Comments: I have a 1991 Porsche 911 964and I just had all the oil lines around the right rear wheel replaced due to cracking and wear. When I take the car out for a ride I still get some smoke coming from that area as if there's still a leak somewhere but I don't see where it's coming from? Any thoughts? Thanks
October 9, 2011
  Followup from the Pelican Staff: Could be residual. If it doesn't go away, jack the vehicle up and inspect the engine for oil leaks. - Nick at Pelican Parts  
diesel Comments: I have a 1977 Porsche 911 Carrera 3.0, the engine work very smooth and no head noises and no smoke from the exaust. Problem is when I drive her hard alot of oil come out from the breather that is attached to the air filter box. What could cause this ? Once no smoke comes out of the exaust, I doubt its the piston rings, or am I wrong ? Please email me any infor to Thanks
October 2, 2011
  Followup from the Pelican Staff: It sounds like you have ring blow-by. You need to do a leak-down test of the engine. - Nick at Pelican Parts  
John Comments: I pulled the heat exchanger last fall but ran out of time before winter to remove the oil cooler. Can the oil cooler be removed to replace the seals with the engine in the vehicle? Thanks for the helpful ideas on how to get the heat exchanger out. That was a fun one.
July 14, 2011
  Followup from the Pelican Staff: It is helpful to know the year and model of the vehicle. In any case, you can look at our tech article - Nick at Pelican Parts  
Dibbydonut Comments: Hi I am very new to all of this..I have a Porsche 911 Carrera Cab. 1998 i have noticed at the rear of the engine under the passenger wheel arch what looks like a stainless steel baffler ??? there is a small amount of oil collecting there, I have had a good look and wiped it clean, but after every trip there appears to be a small amount engine has only done 30,000 from new so could be gaskets worn etc., ?? any help please
May 13, 2011
  Followup from the Pelican Staff: Oil seals and lines harden with age--mileage really does not matter. You can inspect the area to see if the lines to the oil tank or cooler are supplying the stray oil. - Nick at Pelican Parts  
bell222 Comments: I just replaced the thermostat o-ring, the oil pressure switch and the oil cooler seals on my 84 911. I did not have to drop or partially drop the engine, and did not need to remove the heat exchanger. Wasn't easy and it took a couple days but it can be done. The seals in the oil cooler did not seem to harden like the thermostat o-ring and I kinda wish I wouldn't have pulled except it allowed me to really clean the oil cooler which has to help with cooling.
April 17, 2011
  Followup from the Pelican Staff: Thanks for the additional info. We appreciate it.
- Nick at Pelican Parts
Got Porsche Comments: My 79 SC needs new seals in the thermostat, breather and cooler. There are 3 ways to reach these; engine drop, partial engine drop, or remove the CIS system. I would prefer to stay away from the engine drop. So what is preferable, partial drop or CIS removable. Last year I successfully installed the new chain tensioners, so i have some skills. I go slow and careful.
April 4, 2011
  Followup from the Pelican Staff: Thanks for the additional info. We appreciate it.
- Nick at Pelican Parts
zorro Comments: Have a 993 with severe oil leak covering the rear right hand wheel/brake area also leaking forward along the skirt on that side-two ? One nickel plated pipe to oil cooler rubber hose with jubilee clip seems to be the source- any suggestions as to the fix?
March 6, 2011
  Followup from the Pelican Staff: I would recommend replacement of this hose, although you can also remove the hose from the car, and then you can take it to a repair shop where they can re-swage it back onto the metal connection. - Wayne at Pelican Parts  
moparmike Comments: great article I have a 1987 911 carrera 130000 miles just finished install fabspeed full exhaust sweet !!! new oil lines etc . just started it up now she is leaking from in between engine and cooler never leaked before. very cold inside my garage about 28 degrees. a drop about every 15 seconds i dont like oil leaks it makes a clean engine look dirty. car was very well maintained and is all original.except for what i did . i know oil likes to travel but it is def from pass side by oil cooler
bought the seals from pelican how much of a problem is it too get the cooler out on my car 1987 911
January 11, 2011
  Followup from the Pelican Staff: Access is tight, but you should be able to remove the cooler and replace the seals with the engine in the car. The nuts on the top of the cooler will be most difficult to get to, from the back of the engine compartment, under that small rear air guide piece. - Wayne at Pelican Parts  
William Comments: I a 1991 carrera 2. The blower fan works, but the heater doesn't. I have tried turning the heater control knob backward and farward and nothing happens. What do I need to check or do next?
January 4, 2011
  Followup from the Pelican Staff: There are heater flapper boxes located in the rear of the car, above the transmission that control the flow of hot air from the engine compartment to the front vent units. It sounds like this mechanism may not be working properly. On the later cars, this is controlled electronically, so the whole system may be not getting the proper signal from the controller. I would lift the car up and check these flapper boxes first. - Wayne at Pelican Parts  
G91-911 Comments: I have a 91 C2, leaks oil like a sieve. It was diagnosed as the rear engine seal problem, and the solution given was - rebuild the engine. That is not a cheap fix. The car has 244k miles, drives like a champ, handles beautifully, burns no oil, just ... leaks it! Any advise?
December 28, 2010
  Followup from the Pelican Staff: There are actually two seals back there, one that fits inside the nose bearing, and one that is an o-ring around the outside of the nose bearing. The o-ring cannot be replaced without an engine rebuild, but you can replace the outer pulley seal if it's leaking. If you take a look at my Engine Rebuild book, you will see information on how to do this in there. - Wayne at Pelican Parts  
jonplayer Comments: I have a 1988 targa that has intermittent heavy smoke coming out of the tail pipe. The car runs smooth other than the smoke any suggestions ?
October 10, 2010
  Followup from the Pelican Staff: You could have worn valve guides causing the smoke. I would have the engine inspected. - Nick at Pelican Parts  
Jimbones Comments: Smokey heat exchanger was removed, drained, and cleaned. Reassembly will include installation of new oil return tubes and seals just to eliminate them as leak sources for the future. I'm searching for potential sources of oil from above that could drip onto the heat exchanger. The clamps of oil line to the MFI pump was a little loose, but nothing glaring. What are the likely culprits? Also ... would torquing the cam box and cylinder head do any good? Is it even possible to with the engine in the car? Thanks!
September 6, 2010
  Followup from the Pelican Staff: Oil cooler seals, oil pressure sender, thermostat o-ring, case through-bolts, cylinder head to case surface, and the mating surface between the heads and the cam towers - all can leak. Tightening down the head bolts with the engine in the car is okay to do. - Wayne at Pelican Parts  
Jimbones Comments: More on "left turn smoke" ... It's pretty bad sitting level on my garage floor with the left rear wheel off. I think your first suggestion that what is in there sloshes into the exhaust tubes inside the heat exchanger "wrapper". Or maybe there is a left-turn leak and what I see in my investigaton is just burning off the residual?? But, how the heck does oil end up inside the heat exchanger in the first place? I don't see an obvious path.
Thanks for the attention to this annoying problem.
August 17, 2010
  Followup from the Pelican Staff: Oil can only get inside the heat exchanger from an oil leak. Even if it were leaking out the exhaust when the car was off, it would stay in the exhaust. Guaranteed, you have a current oil leak, or had one in the past. I would remove the heat exchanger, turn it upside down, and see if you can drip the oil out that is in there. Odd though, as oil trapped in there typically does burn off with just regular exhaust heat. - Wayne at Pelican Parts  
Jimbones Comments: Is it possible for oil to get into a heat exchanger?
My '72 911 w/MFI smokes from the outlet of the left heat exchanger ... not from oil dripping on it from a valve cover, or injection pump drive oil seal at the driver's side cam shaft. The SSI sheet metal looks sound.
Smoke comes out just like warm air would to heat the cabin as soon as the exhaust hardware heats up. When driving every left turn makes the problem worse for a few minutes. H-m-m-m...? Any ideas?
August 16, 2010
  Followup from the Pelican Staff: It's possible to get oil in there, but really only from a previous leak somewhere. Typically when these have an oil smell, and you fix the leak, the oil burns off in a fairly quick amount of time. It sounds like there is a pool of oil in there and when you go around a turn, it's hitting the exhaust pipes and getting heated. Or, you have a leak that only happens when you turn left. I would turn left, then quickly get out and look under the car to see if you can see anything leaking there. - Wayne at Pelican Parts  
Daddy Comments: I have a 1988 911carrra 41,000 original miles engine oil leak
all seals and gaskets replaced 7-1-10. oil is leaking inside bell housing in front of fly wheel. technician thinks it is seeping thru wall of engine case even after using marine poxy
on said walls. Thank You
July 15, 2010
  Followup from the Pelican Staff: Not likely to be seeping through aluminum. More likely is that there may be some plugs in there that have not been fully sealed. The area needs to be fully cleaned and then re-epoxied. See my Engine Rebuild Book for details on this. - Wayne at Pelican Parts  
Chuck Comments: Thanks..more specifics on smoking problem. 1976 911 targa

Oil leak at cam shaft housing where cylinder head bolts to cam shaft..leaks to exhaust heads
June 25, 2010
  Followup from the Pelican Staff: That type of leak (if it's really from there), is not fixable without rebuilding the engine. I would probably just learn to live with it, or get ready to tear the whole engine down. See my Engine Rebuild book for more info... - Wayne at Pelican Parts  
Chuck Comments: 1976 911 Targa..smoke problem. Took car for valve adjustment returned with severe smoke problem. Tech states it is not a valve cover issue but can't id leak suggest engine replacement.
June 24, 2010
  Followup from the Pelican Staff: Is the smoke coming out of the tailpipe, or is it from oil dripping on the heat exchangers? If it's dripping on the heat exchangers, then it's definitely a valve cover tightening problem (tech probably over-tightened the valve covers). So, you took the car in for a valve adjustment, and the tech messed it up, and is now recommending an engine rebuild? Sounds like it's time for a new tech. - Wayne at Pelican Parts  
Arthur Comments: Excellent site ! Since you know the 911, I would like to ask you a question. I have a 1991 Porsche carrera 2 100 000km
What transmission fluid ???
Thank you
April 11, 2010
  Followup from the Pelican Staff: I would one of these: - Nick at Pelican Parts  
Mascot100 Comments: Removal of the heat exchangers is not required - the oil cooler is completely accessible with them in situ!
March 26, 2010
  Followup from the Pelican Staff: Thanks for the additional info. We appreciate it.
- Nick at Pelican Parts

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