1986 911 Oil Cooler Leak

[fredheiler]

I'm posting my recent experience just in case it's helpful to anyone. My good-running '86 911 developed an oil leak that dripped on the exhaust crossover pipe, making for annoying smoke. I power-washed the underside, started it up and thought I saw oil leaking from the engine-trans seam. That sounds like a leaky flywheel seal, but it seemed unlikely on a car with only 53,000 miles. I heard it can sometimes be the oil thermostat o-ring (top of the block, directly above), so I removed the right-side intake manifold and replaced the o-ring. Still leaked oil.

Now sure it was the flywheel seal, I pulled the engine-trans unit and replaced the seal (also replaced the trans mainshaft seal that's hidden inside the throwout bearing tube). The old seals were pliable and seemed in good shape, so I was still puzzled about the source of the leak. In the process, I noticed the clutch disc was worn into the rivets, so I replaced the clutch assembly, including the flywheel (at least that made the long process worth it).

When I started it up, it still had the same leak! I ran the engine for a while on the lift, looked around carefully, and now it seemed to be coming from the oil cooler seals! So I've removed the cooler (it came off easily, WITHOUT doing a partial engine drop) and have replaced those seals.

However, the four nuts that hold the oil cooler were tight, and the old seals were pliable, so I'm worried I have not yet found the culprit. I understand there are only two more possibilities -- a crack in the oil cooler itself, or maybe the switch for oil pressure light). Stay tuned.

[ab1752]

I, too have had something going on around the oil cooler for some time. The seals have been replaced twice and the oil pressure switch seal, so I believe it is leaking from the fins per the image below. I do not see how this path of oil from the fins could be from something else, and will likely order a new cooler asap.

[proporsche]

it is very rare that the oil cooler leaks ..it is most likely the triangle of death (engine top oil leak) and possibly this place...

[ab1752]

In my case, the triangle of death has been addressed, and really scrubbed. Could it be the case? Perhaps, but the oil is definitely coming from those fins, internal to the cooler.

If it was the case leaking, I don't see how that oil could make its way to the fins, then drain out the bottom...the cooler is sealed on the case side, correct? In my case, the other suspect to have oil leaking out the fins would be the oil pressure switch...possible, but it was very recently changed. Thanks all...hope the OP tracks this down.

[HarryD]

FWIW. I had a similar issue. In the end, after eliminating all the usual suspects, it was an internal leak in my 48 yr old cooler.

My story: https://forums.pelicanparts.com/porsche-911-technical-forum/1095055-failed-oil-cooler.html

[boyt911sc]

Fred,

Is the oil leak still unsolved? If you have not done the 100 psi. immersion pressure test to your oil cooler, I would be more than happy to do it for you. We are not that far from each other. PM if you are interested.

Tony

[Matt at Pelican Parts]

Searching through the 911 technical articles there is one here that covers oil leaks pretty well. It's worth checking out as it goes into detail about checking the oil cooler and other common places leaks occur. It also mentions the oil lines and various seals as possible culprits.
https://www.pelicanparts.com/techarticles/101_Projects_Porsche_911/21-Oil_Leak_Fixes/21-Oil_Leak_Fixes.htm

If you do find it is the oil cooler I'd check out this great write-up on replacing it while the motor is in the car.
https://www.pelicanparts.com/techarticles/911_oil_cooler_repl/911_oil_cooler_repl.htm

Hope this helps!
-Matt

[pete3799]

I had to replace my oil cooler do to a leak. Bought a used one and it fixed the problem.
I made a pressure tester to find the leak. I'd take Tony up on his offer or if you want i can send you my home made tester.