911sport

After having owned an SC for a year now, and having been through a couple of oil leaks, I'm beginning to think a lot of the problems with leaking oil in these cars is from a lack of adequate heat exchange to cool the oil.

I have the trombone type of heat exchanger in the front right tire well--which is nothing but a couple of coils of the oil tubing. I understand better cooling and lower oil temperature is achieved with a radiator.

Today was a hot day here in PA, and there was some traffic on the highway. The temp gauge climbed to 200-220F (9 oclock), and for the first time since last fall, I splashed a bit of oil as I was coming down the driveway. This past winter, the temp never climbed above 180-190F, and I never saw any signs of leaking. The leak is in a place hard to get to without removing the engine--and it's a minor leak anyway--just happening when the oil temp climbs above 200F, it appears. Doesn't leak when cold--in the garage.

So, I'm wondering if a radiator type of exchanger might solve the leak problem by dropping the oil temp? Can't say for sure, but worth a try depending on how much a radiator exchanger for an 82SC costs?

Steve Weiner-Rennsport Systems

Hi:

You've asked an EXCELLENT question,...

IMHO, the frequency & occurrance of oil leaks as well as overall engine longevity is directly related to oil temperature management.

When one controls the maximum operating oil temp between 180 and 200 degrees F, one can truly reduce the frequency and severity of oil leaks in these engines. If the oil temps are allowed to run above 200 deg F (even reaching above 230 deg F), all of the O-rings, gaskets and seals are subjected to the extreme heat that hardens and dries out these elastomers. This results in drips and leaks from many joined surfaces that have lubricants behind them and mandates disassembly for replacement; not a cheap endeavor.

Its FAR less expensive to operate proactively about this and contain/manage peak oil temps for maximum engine durability and a dry engine. This is accomplished with the installation of effective oil coolers and ducting air to these "heat exchangers".

In your example, the trombone cooler is well known for not its inability to maintain the cooler temps needed to prevent leaks as well as maintain peak performance in hot weather. We replace that trombone unit with a Carrera cooler and its fan to help contain oil temps in traffic.

Hope this helps,

Mike Murphy

Steve, I have an 88 Carrera and experienced up to 240F on a DE event in an 80F day. I, too had some oil leaking from the chain covers in greater amount that on the street. I will now replace those gaskets.

My question is, how can I easily get my temps down? I think 240F is too hot. Should I focus solely on the external cooler? I have never cleaned it out or inspected the fan in there.

ron mcatee

Murphy, you can replace that 244 degree F thermostat in the oil coller with a lower temp one. I did it using a 99 dergree C BMW radiator switch from Pelican. Cost was Approx $12. I wanted it to come on automatically like it should, but at the lower temp. Mine has always run at 210 F or below since I changed it. there is a lower one at 91 C, but Steve and Pete Z suggested I not go that low or the fan on the cooler will run almost constantly and eventually burn up. Your other option is to leave the system as is and put in a switch to activate the fan at a lower temp.

911sport

Thanks, Steve. Where to get a Carrera cooler with fan, and how much $$?

I checked the thermal conductivity of water vs oil below 100 C , and water is higher by a factor of 4. What was Ferdinand thinking. The caveat is these engines seem to last a long time--maybe for other reasons.

Mike Murphy

I'll tell you what he was thinking: In an interview during a race, many water-cooled proponents were asking the question, "why air-cooled?" Ferry's response was, "because we never lost the air." In race terms, when you lose something it means it breaks. If you lose the water in a liquid-cooled car, you lose the race. If you lose the air in our environment, that means that you're not on the planet earth. So it just removes one variable in the reliability equation.

Of course, the belt could fail on the fan, so nothing is perfect...

Steve Weiner-Rennsport Systems

You are quite welcome.

I would call the various Porsche dismantlers and see what they have. Any & all used oil coolers MUST be ultrasonically cleaned before use.

Air-cooling, while not the best for HP, is VERY simply & reliable and thats precisely why Dr. Porsche used it. As long as one controls oil temps, one has no problems.



Murphyslaw:

You are right, 240 deg F is FAR too hot and you need to do something about that. Oil coolers are heat exchangers and without sufficient airflow, they are not very effective. I would pull the front valance to ensure that the front is totally clean and then pull the foglight to get some air to the cooler.

We even delete the foglights and cut away the mounting bar to present an obstruction-free opening for good airflow.

911sport

Pelican has the complete radiator/fan package for $1500 or so. Wayne Dempsey's 101 projects book covers the instal, which looks to be a 5-6 hr deal. Aside from the cost, the front inside wheel mount of this radiator requires opening up the right side of the front end to let cooling air in, and that could interfere with the action of the spoiler on the lower front end of my SC which cuts uplift forces. The latter balances with the downforce in the rear created by the teatray spoiler. That could be significant at highway speeds and certainly on the track.

Zims carrys an oil cooler which mounts on the engine for 72-89 911s for $370. Looks like a radiator type. I don't think there's a fan, but with a teatray type of tail like my SC has, you should get a good airflow down to help cooling, if only at higher speeds. I don't know where it would mount--but the price isn't bad. If it's under the teatray, it would be in the right place to receive cooling air.

Do you have any thoughts on the Zims cooler? I haven't phone them about it yet. Bought a rebuilt WUR from them last fall, and have been well satisfied starting through the winter.

When you read up on the efforts to improve the oil cooler in the front through the 80s cars (from brass tubing to radiator to radiator/fan), you realize this has been an ongoing problem for the air-cooled 911s and undoubtedly related to the frequency of oil leaks.

Steve Weiner-Rennsport Systems

Front lip spoilers and teatray spoilers do not create ANY downforce; all they do is cancel some lift. Adding cooling holes for brakes or oil coolers makes no discernable difference in lift cancellation. This is one I've tested extensively for 30 years,...

Engine oil coolers should not be installed in the rear spoiler no matter what kind it is. This is an area of turbulent, non-laminar semi-low pressure. Oil coolers require high-pressure air to be effective however one can install a transmission cooler back there (not ideal).

psalt

Today was a hot day here in PA, and there was some traffic on the highway. The temp gauge climbed to 200-220F (9 oclock), and for the first time since last fall, I splashed a bit of oil as I was coming down the driveway. This past winter, the temp never climbed above 180-190F, and I never saw any signs of leaking. The leak is in a place hard to get to without removing the engine--and it's a minor leak anyway--just happening when the oil temp climbs above 200F, it appears. Doesn't leak when cold--in the garage.


If your oil leak is near the bellhousing, it may be a failing oil pressure switch. The plastic insulator deforms with heat and the leak can start and heal itself a few times before completely failing. You can replace it without dropping the engine.

As for air cooling, Porsche had nothing to do with it. It was in the spec for the original KDF/VW, Hilter told Porsche to copy many of the VW/Porsche design features from Hans Ledwink's Tatra because the car had to be reliable from Africa to the Arctic.

911sport

Thanks for the info. It isn't a serious enough issue yet for the amount of driving I do.
The smaller engine size may have had something to do with adopting air-cooling. They finally switched to water-cooling in the last 10 years with the bigger engines. The SCs were kind of in between in engine size. I know in hotter climates, in Texas for example, everybody uses the radiator type front cooler.The trombone type isn't sufficient there.

psalt

The stock oil cooling is fine for a street driven SC. If your oil temps went up after prolonged idling, check your ignition timing. The lambda SC's used a crude vacuum retard to meet the curb idle HC emission test. It also causes measurably higher engine temps at idle. If you plug the gray hose at the back of the distributor and reset your idle speed and timing to spec, the hot idle temp will drop and stabilize.

911sport

Steve: I spoke to a Zims rep this morning. Their oil cooler is the standard cooler attached to the engine I already have. It's a replacement part. He's in Texas and says everybody down there has to use the radiator type cooler in the front. The trombone isn't sufficent. But he says it should be OK in PA. I don't see temps any higher than the 9 o'clock position in the summer, which is around 210F. He said that temp shouldn't be an issue.

Downforce vs lift--sure, I agree--it lessens the lift and doesn't create a downforce. I was using them interchangeably, but it's not the same.The rear spoiler significantly reduces lift (downforce?), and improves air flow into the engine compartment. That has to have some cooling effect at higher speeds.

Front air intakes are used extensively in these cars now for cooling, so clearly that's the way to go. Thanks for your input.