Disable 911 oil cooler thermostat?

[bpolonsky]

I have an oil leak just forward of the external thermostat for the front oil cooler on my 1978 911SC. The leak occurs only after the oil comes to temp and the thermostat opens. The car does not leak when parked. Both lines were replaced several years ago and were ok until recently. I tried disconnecting both lines at the thermostat, cleaning the mating surfaces and reattaching without solving the problem. I do not use the a/c, live in a cool climate and never drive in traffic. Until I replace the leaking oil line, is it possible to keep the thermostat in the closed position so that the oil does not circulate through the lines to the cooler? Any other ideas/suggestions to find the leak are welcome Thanks.

[Formerly Steve Wilkinson]

I assume the leak is at the nut that holds the line to the thermostat. You did the right thing by cleaning the mating surfaces, as even the most minuscule bit of schmutz will cause a leak. The next thing I'd do would be to seriously torque down the nut. Tighten it and then tighten it some more. that's how I fixed my similar leak, though it was on the entry side of the thermostat. Don't know that there's a way to force the thermostat to stay closed--my manuals are packed away following a recent move, so I'm not sure whether there's a spring you could add or remove or a plug you could temporarily insert.

If the leak indeed is at the nut and not a fault in the line itself, I'm not sure what replacing the line would accomplish.

[Liam O]

maybe some thread tape that heating engineers use would be good for this if its leakin at the joint,could be worth a try

[boyt911sc]

Originally Posted by bpolonsky

I have an oil leak just forward of the external thermostat for the front oil cooler on my 1978 911SC. The leak occurs only after the oil comes to temp and the thermostat opens. The car does not leak when parked. Both lines were replaced several years ago and were ok until recently. I tried disconnecting both lines at the thermostat, cleaning the mating surfaces and reattaching without solving the problem. I do not use the a/c, live in a cool climate and never drive in traffic. Until I replace the leaking oil line, is it possible to keep the thermostat in the closed position so that the oil does not circulate through the lines to the cooler? Any other ideas/suggestions to find the leak are welcome Thanks.

bpolonsky,

The oil line to the auxiliary cooler (trombone or Carrera) is always open!The oil starts to circulate when the temperature gets hot (180°F) and gradually opens the slide valve (return). In summary, the oil lines and auxiliary cooler is filled with oil once the engine starts to run. However, since the temp. is below the operating temp. of the auxiliary thermostat, the oil is not circulated at this point in the auxiliary cooling system. The oil circulation is done by the engine oil thermostat and returned to the oil tank.

As the temperature builds up (180°F plus), the return slide valve (aux. thermostat) gradually diverts the hot oil from the engine via the auxiliary cooler. There is a thermostat saver kit available from our host and they work great.

Tony

[ChrisBennet]

Originally Posted by Liam O

maybe some thread tape that heating engineers use would be good for this if its leakin at the joint,could be worth a try

The lines to the thermostat do not seal at the threads so teflon tape won't help unfortunately.
-Chris

[JFairman]

Originally Posted by boyt911sc

bpolonsky,

The oil line to the auxiliary cooler (trombone or Carrera) is always open!The oil starts to circulate when the temperature gets hot (180°F) and gradually opens the slide valve (return). In summary, the oil lines and auxiliary cooler is filled with oil once the engine starts to run. However, since the temp. is below the operating temp. of the auxiliary thermostat, the oil is not circulated at this point in the auxiliary cooling system. The oil circulation is done by the engine oil thermostat and returned to the oil tank.

As the temperature builds up (180°F plus), the return slide valve (aux. thermostat) gradually diverts the hot oil from the engine via the auxiliary cooler. There is a thermostat saver kit available from our host and they work great.

Tony

Thats not how it works on my '87.

Oil is pumped from the scavenge side of the engine oil pump out of the engine case to the external thermostat next to the passenger side spring plate. If the oil is not real hot then that thermostat routes it back to the oil tank where internal piping inside the oil tank sends it directly through the oil filter and then into the tank.

When the oil reaches around 180 degrees the external thermostat opens and diverts the oil to the front oil cooler, then it comes back and goes to the oil tank/filter etc.

When the oil is cold there is a small amount of pressure still going forward to the oil cooler but not much. My car has a large horizontal B&B oil cooler in front and it has a drain plug. If I start the car cold with that plug removed just a little oil will dribble out. I havn't tried that when the oil is hot because it would probably make a huge mess...

After the oil is filtered and sitting in the oil tank it is sucked back into the pressure side of the engine's oil pump through the large "S" shaped oil hose. From there it goes to the internal thermostat which sends the oil directly to the main bearing oil galley, and from there on to the cam towers and chain tensioners through the small external oil lines at the back of the engine. When the oil is hot the internal thermostat diverts the oil through the engine mounted oil cooler before it goes to the main bearing oil galley.

It's easy to see how it all works in this diagram...

[bpolonsky]

Thanks to everyone for your advice. I think I'll try one more time to clean the mating surfaces and increase the torque on the nuts.

[Formerly Steve Wilkinson]

Exactly what I'd do. If you have the "official" Porsche oil-line wrenches, which is what I use, you'll notice that they're designed so you can slip a two-foot (or whatever) length of steel pipe over the end of the wrench for increased leverage, so you can imagine how much twist they're capable of imparting.