Stephen Masters

I have a 1978 911 SC that gets hot during a track session. It will go to redline if I don't pull into the pits. I have an external oil cooler in the front fender. I removed the Headlight and drilled holes in the bucket and still overheated. The car started to loose power and the green oil light blinked on and off.

I have searched the archives and found information regarding "oil cavitation” and replacing the oil pickup, and pressure relief valve.

How difficult are these fixes to do… I.e. does the case need to be split.

The Porsche dealers are having a tough time finding information out about this as these bulletins are pretty old.

I have just added Bilstiens, turbo tie rods, lowered and corner balanced the car and it is too much fun at the track if only I can get it to stop overheating.

Any help will be greatly appreciated.

Thanks Steve

Elephant Chuck

Stephen

Why do you suspect cavitation? Do you see a sudden loss of oil pressure at any time? I'd say that is unlikely to be your problem.

Taking these cars to the track really stresses the oil cooling system, overwhelms it in many cases. You really have to beef up oil cooling if you are going to the track.

A few questions -

What type of fender cooler do you have? The SC stock loop cooler isn't going to cut it.

How hot does the oil get in normal street driving?

Have you tested the external tstat for proper operation? Put your hand on the oil lines and see if they are hot.

Have you tested the internal tstat for proper operation? Carefully put your hand under the fins of the internal cooler, it should be too hot to touch. It should have air blowing through it.

With that information, it would be easier to make a useful recommendation.

Chuck

Trak Ratt

Chuck mentioned most common problems, but don’t forget to check the hard lines running up the right side of the car. I have yet to see either of them that didn’t have some damage from improper jacking that hadn’t just been replaced. Also, I think I remember seeing the Tech Bulletin on early SCs oil pickup tubs & relief valve upgrades in the “74-89 911 Parts Book”. This book also has most other Tech bulletins for these years & is very useful as a reference. The bulletin also list the replacement part numbers too. The actual repairs are simple, or as simple as anything else on SC engines. Your dealer’s Parts Department should have access to all factory bulletins on their parts database, they certainly pay enough for the system! The book should be about $10.

Bill Gregory

Steve,

You've probably already read the 911SC FAQ where the oil updates are talked about, as well as the article on tech.rennlist.com on 1989 and earlier 911 engine cooling.

There was an April 1989 article in Panorama ("The 911 Lubrication System" by Alan Caldwell) that covered this in more detail. It's also reprinted in Up-Fixin Volume 8. The PCNA bulletins you're looking for are:

* PCNA Technical Bulletin 78-03 "Oil Pressure Relief and Safety Valves" (PCNA Technical Bulletins prior to Nov 84, PCAN Publication PNA 000 056, September 1987, page 123)

* PCNA Technical Bulletin 83-06 "Crankcase and related parts" (PCNA Technical Bulletins prior to Nov 84, PCAN Publication PNA 000 056, September 1987)

* PCNA Technical Bulletin 85-10 "Oil Pump" (PCNA Technical Bulletins Nove 84 - Dec 85, PCNA Publication PNA 000 028, pages 75 and 76)

Note, the safety valve and pressure relief valve changes were made starting with 911SC engine number 628 2539 (49 state) and 658 1060 (California).

Stephen Masters

Chuck

I have a carrera fender mount cooler that we measured temp going in at 251 and coming out at 190. so I think that means the cooler is working.

As the temperature went higher, I started to notice a lack of power and the green oil light flashed a few time before I pitted and let the car cool down.

Elephant Chuck

How did you measure the in/out temp of the oil cooler? With the car running and parked? Do you have a fan on that cooler?

251 in and 190 out actually sends a red flag because it is too much temperature drop for 1 pass through the cooler. Especially if you are measuring this with the car sitting still (no airflow, even with the fan that is a huge drop).

Makes me suspect the oil is moving through the cooler much too slowly. This big temp drop could be caused by poor flow rate through the system. Potential causes are external tstat that is not opening fully or crushed oil lines (as mentioned above).

Tom F

I had exactly the symptoms you describe, except they occurred at sustained high speeds on the highway in my '79 SC. The cause turned out to be failure of the welds in the "improved" oil pump pickup screen/baffle plate, which I bought brand new from the Porsche dealer. Returning to the original plain screen solved the problem for me. It seems that the baffle plate was drifting down to partially obstruct the oil pump intake at the sustained high speed, high flow conditions. Pretty obscure, but worth mentioning, in case you've tried the same "upgrade."

Stephen Masters

I drained the oil and removed the sump cover to find the old style sump intake i.e. a straight pipe. The next questions is how do I replace this with the new style sump pickup ?????

Tom F

You did find a suction strainer behind the sump plate, didn't you? This is an important part, because it takes the bubbles out of the oil, which, as I understand it, is important to preventing cavitation.

The suction pipe itself is glued to the oil pump. You can't change it without tearing down the engine.

The part that gets updated is the screen behind the sump plate. The early style is just a screen with a hole to slip over the suction pipe and a steel flange with six small holes to fit between the sump plate and the crankcase. The later style has a steel baffle plate, with hole, that fits over the suction pipe, and a cylindrical screen around the perimeter, connecting the baffle plate to the flange that fits over the eight studs in the crankcase. Bruce Anderson's book shows pictures of both, I believe. The idea was to smooth the oil flow to the suction pipe, I guess, which sounds like a useful way to improve pump performance, too, but not if the part breaks like it did in my car.

Replacement oil pumps do away with this mess, and have a pickup strainer and baffle plate permanently affixed to the suction pipe.

Based on my experience, I'd be very careful about updating the suction strainer on an old motor. If you have the plain basket strainer now, then I feel that you should look elsewhere to solve your overheating problem.

Jeff Curtis

Stephen, Chuck M. brought up some VERY valid issues (too much of a drop in temp.) - a friend of mine had this same thing happening to him...took his oil cooler off and took it to a radiator shop to have it flushed...all sorts of crap came out, mainly sludge and fine metal particles.

This was a '77 911S, so the oil cooler had been purchased used...probably from someone that blew up their engine?

Another thing to check is the engine mounted oil cooler, that can get clogged as well.

The fact that hot oil is getting up to and through the cooler is a good thing to know...also check for an obstructed/damaged return line from the cooler.

Seems like you're on the right track.

Stephen Masters

I have now ordered a new sump screen( the updated venturi type, a sump gasket kit, and a new insert for my external oil thermostat. I am crossing my fingers that this works.

P.S. The oil cooler is brand new so I doubt its plugged, plus we tested the temps with the car off and a laser pyrometer, so I wouldn't count on those number being accurate.

P.S.S. The only thing that is making me a little hesitant right now is that I checked the oil level as soon as I got the car off the track and I didn't notice any foamy oil. While I wasn't looking for that I would suspect that I would have seen that had the oil been cavitating.

"I'll just keep my fingers crossed"

Thanks all for the help.

Ed Bighi

Sounds strange since I have been running an sc at track events in Phoenix (it's pretty hot here) for years with only the loops and have never had that happen. Same with my friends. Though I do see some cars running cooler than others with the same equipment. I suspect it could be an oiling problem also.