Occasionally it may be necessary to remove an internal 911 oil cooler while the motor is still in the car. Whether to replace the seals, or to replace a damaged cooler, removing and replacing the cooler does not require the removal of the motor from the car. Before deciding to replace the cooler or replace the motor to cooler seals, determine that this in fact the source of your leak.
First make sure that the sender unit on top (top rear when looking into the engine compartment) is not leaking. Second, get a good light and get under the car (with car on jack stands). Shine the light around the oil cooler. If the cooler leaks when the car runs, it will continue to leak for a while after you shut the car off. Look into the center of the cooler. If oil is coming from there, chances are it is a bad cooler. If oil is coming from where the cooler and the motor mate, you MAY have bad seals, a bad cooler, or another source of oil (remember, oil creeps and wanders around, often times ending up quite a distance from the original source). If the oil is seeping from where the cooler and the motor mate, you may consider checking the torque of the nuts before removing the cooler.
It has been a while since I have changed an oil cooler on a motor still in a 911, so the following are the steps as I remember them:
1) Jack up rear of car and secure properly (chocks, jack stands)
2) Drain oil
3) Remove right (passenger) rear wheel (it is not necessary to remove the 1/2 shaft)
4) Depending upon your setup, you may want to remove your heat exchanger or header (right side, 4-6 only)
5) Remove sheet metal separating upper and lower rockers and remove the bolts connecting the rear sheet metal to the oil cooler
6) Disconnect the tank to cooler oil line (be prepared for more oil to run from the line and/or cooler)
7) Although it is not necessary, you may want to remove the motor to tank line at this point because it will give more room to pull the cooler off and to re-install one later
8) Depending on what year motor you have, and whether there have been any updates to the shroud, this step could be easy or a pain. Part of the fan/cooling shroud on the top of the motor wraps over the oil cooler. This of course forces air through the cooler, cooling the oil. On early cars (up to SCs I think), the shroud included a separate "plastic" tunnels that was riveted to the fiberglass shroud. The tunnel included a wrap around end cap for the oil cooler. On later cars, while the shroud still included the tunnel, the end cap that fit over the cooler was not an integral part of the tunnel. If you have a later car or one that has been updated, simply remove the end cap with a 10mm socket (there will be at least a couple holding the cap to the cooler and at least a couple bolts holding the cap to the shroud and/or motor. Once you have removed the cap, simply use a 13mm socket and extension to remove the two upper nuts holding the oil cooler in place.
On earlier motors that do not have an updated shroud, infinite patience or a little ingenuity is required. Remove all the bolts holding the shroud in place in the area on the motor around the cooler. While the integral end cap is fairly rigid, you still may be able to use an extension with universal joints to reach under the cap/shroud with a 13mm socket to remove the two upper nuts holding the cooler in place. If you are finding it too difficult to snake the socket under the shroud (there is also a baffle under there too), you may consider buying a new motor with the updated cooler cap. Failing the new motor option try drilling out the rivets that are holding the tunnel in place on the shroud around the cooler (these can be re-riveted later, or screwed in place). Once you have the tunnel more flexible, it should allow plenty of room to get up under the cap and remove the two upper nuts holding the oil cooler in place While it is not absolutely necessary to remove the rivets from the shroud, it will assist in removal of the cooler, it will assist in re-installation of the cooler, and will certainly save the neighbor's ears from what undoubtedly will be an education in vulgarity.
9) Once the two top nuts are removed, remove the bottom nuts from the cooler. If all the sheet metal screws and shroud bolts are removed, at this point the cooler should essentially fall into your hands (along with a 1/2 of quart or so of oil all over your lap!). If the shroud end cap is in place still, you may have to fidget with the beast to get it clear of the studs and shroud (and possibly header);
10) To quote a phrase used too often in the factory manual, "installation is the reverse of removal!" Actually, with this project, reversing the removal process might finish it for you, with a few additional points noted. When re- installing the cooler, use either a new or tested one that has been cleaned. I would recommend at least testing the one removed unless it is OBVIOUS that the cooler is trash (hopefully in the not too distant future I will be fabricating an affordable oil cooler tester, but that is another story). Use a generous amount of Dow 111 (or grease) on the new seals to keep them in place (as well as provide proper sealing) as you re-seat the cooler. Make sure you use new spring washers and torque the nuts to the proper specification. Re-connect all sheet metal and shroud bolts (the shroud and sheet metal are critical in providing proper cooling). If you have drilled out any rivets, re-rivet or screw the tunnel back in place. Obviously, after putting everything back together and filling up the oil, check for leaks.
Hope this helps. If anyone has any questions or comments, let me know.
Steven M. Stomski