1983 Porsche 911sc

[carnuts]

Hello everybody, I am having a strange situation with this 1983 911sc. The engine runs perfect, the oil cooler on the front was upgrade, the oil thermostat/regulator is new, the thermostat on the engine is new, engine oil cooler has been clean, engine was inspected for any debris accumulations on top of the cylinder heads, I am running Total synthetic oil 5/40w, oil temperature sender is new. This is the situation, oil temp and oil level are normal, but if I am on the freeway for 15 or 20 minutes, everything is normal and all the sudden the oil level drops instantly to zero and the temp. start going quickly up. After pull over is no oil in the tank, the front oil cooler is pretty hot and in 10 minutes oil start filling the tank and the temp drop to normal. The oil pressure was not affected at any time and was normal.

Any Ideas?

[LIRS6]

The lack of oil in the tank would likely relate to the thermostat opening as you reach ~185 degF, diverting oil to the front cooler, as it was designed to do. When you measure the oil level with the dipstick when the engine is hot and running, what does it show? I'm not an expert on the subject, but to my understanding our engines (3.0) do not take well to synthetic oils. Suggest to do a search ref oil, to ensure that you are using what is appropriate for your engine.

Jason

[75 911s]

Sounds very low on oil. As mentioned, oil is being diverted to the front cooler at temp. Allow vehicle to warm up and then check the level at idle on a flat surface. You are probably low several qts.

[ischmitz]

The first rule for these cars is: The oil level is measured with the tank dip-stick with the engine idling at operating temperatures and car on level ground. Most prefer to have the level at low to mid-range to reduce amount of oil ingestions through the oil breather system back into the intake.

Any other method can cause issues:

- The internal oil level sender is not accurate and can be way off
- Measuring with engine cold will lead to overfill and all sorts of issues with oil getting into the intake system.

These engines are dry-sump engines. In contrast a wet-sump engine measures oil level with the engine at rest in the engine sump.

The topic of synthetic vs. dino has nothing to do with the oil level unless we factor in a very tiny difference in thermal expansion coefficient or aerating tendency. There are other implications and tons of discussions about the merits, differences of different oils. Do a search and you will see. Most recommend an oil with good additive pack.

Welcome,
Ingo

[LIRS6]

Originally Posted by ischmitz

The topic of synthetic vs. dino has nothing to do with the oil level unless we factor in a very tiny difference in thermal expansion coefficient or aerating tendency. There are other implications and tons of discussions about the merits, differences of different oils. Do a search and you will see. Most recommend an oil with good additive pack.

To clarify, my comment was only in respect of the type of oil best suited for a 3.0 - not that synthetic oil would contribute in any significant way to the volume of oil.

Jason

[ischmitz]

Two variations of a theme/theory always come up here:

- changing to synthetic in an engine that ran with dyno forever has a tendency to increase leakage. Some say that’s because the swelling of O-rings is different when a different oil is used.

- synthetic oil caused more leaks in general because it’s molecules are smaller and get through leaks easier.

Then some say:

- Porsche specification says “use dyno” so stick with it.

Being a chemist the second statement doesn’t make sense to me at all. For the first I could see where a dyno oil leads to different swelling compared to a synthetic oil on a new o-ring gasket. However I assume the gaskets in a well-used engine are already saturated with the dyno oil and compressed and hardened at the same time. A theory where the synthetic oil starts to replace the dyno oil in the compressed hardened o-rings seems far-fetched. But then maybe there is real data where one finds dyno -> dry, synth -> leaks, back to dyno -> dry again.

So I’m not saying it’s completely impossible for the synthetic oils to reduce the swelling.

Fact is there are lots of modern synthetic oils with more modern and different properties that weren’t available when the specifications for the 3.0 or any early engine was derived. That doesn’t mean a synthetic isn’t as suitable as a dyno. However the early 911 engines don’t like the additive packages geared towards modern engines. They want to have high Zink levels. That’s where the confusion comes in.

[TibetanT]

Carnuts:

First, some here have given you very good suggestions with what to do. IT does sound like you do not have enough oil within the system. (Usually takes 10-11 quarts when system has been drained/empty).

When I have done any oil change/maintenance I add 8quarts, then another one or two quarts and check the level after reaching running temperature. I run only 15W/50 Mobil 1 Synthetic in my 1983 911SC since I got it.

I am not trying to start an Oil Thread either. Take a look at the owner's manual for the best "weighed" oil for your area. (You have not posted "Where" you are, so just a suggestion.)
The reason being…I would never run my 911SC with 5W/40; seems to thin an oil unless living in a very, very cold environment. Just me though, and I am no expert.

Try searching for "Oil Thread" on this forum…you'll be informed.

Hope this helps.

[porsche930dude]

I would change the oil and see what it does. You should be using a 15-50 or similar dino oil. oil level is checked on a level surface while hot and running it should be mid level. Dont mind the level gauge inside the car it is never accurate.

[Canada Kev]

A couple things:

1. How do you know your oil level drops to zero when you're driving on the freeway? If you're referring to the oil level gauge, it will ALWAYS read at the empty level when you're driving. It will, if working properly but many aren't, only read accurately about 20-30 seconds after the vehicle is stationary and idling on a level surface. Always use the dipstick for accurate oil level with the conditions listed above.

2. There is nothing wrong with synthetic oil in these air cooled engines. Period. It doesn't cause leaks but may clean out the gunk that may have been plugging minor weeps that were pre-existing. Just be sure it has sufficient ZDDP content. If you've been using synthetic for a while and have no leakage, by all means keep doing so. The weight of your oil is also likely acceptable depending on where you are driving. My memory is a bit foggy on this but my manual listed both 40 and 50 weights as acceptable for operating temperatures above 50 degrees Celsius. Which is F'ing hot.

3. As some have suggested, you may be low on oil and when the thermostat opens up on a new, empty cooler, the oil will get pumped there. Normally when you change your oil, the oil cooler loop doesn't drain. That's about two litres. The system holds about 12 total. So when you add new oil, put in about 9 litres and adjust as necessary after the engine warms up and you can check it properly. I'd run it on the lower level of the dip stick range.

[Bill Verburg]

Originally Posted by carnuts

Hello everybody, I am having a strange situation with this 1983 911sc. The engine runs perfect, the oil cooler on the front was upgrade, the oil thermostat/regulator is new, the thermostat on the engine is new, engine oil cooler has been clean, engine was inspected for any debris accumulations on top of the cylinder heads, I am running Total synthetic oil 5/40w, oil temperature sender is new. This is the situation, oil temp and oil level are normal, but if I am on the freeway for 15 or 20 minutes, everything is normal and all the sudden the oil level drops instantly to zero and the temp. start going quickly up. After pull over is no oil in the tank, the front oil cooler is pretty hot and in 10 minutes oil start filling the tank and the temp drop to normal. The oil pressure was not affected at any time and was normal.

Any Ideas?

This sounds suspiciously like an issue that arose on '78 SC, but was cured well before the '83s came out. You mention that oil system has been completely gone through, that may be the root cause of the issue, during assembly the wrong safety or pressure relief valve may have been installed or installed wrong.

In '78 the then new SCs experienced exactly the conditions you describe thought usually only in high speed track use.


You oil is on the light side, from the data Total provides it's also a bit light on the critical ZDDP content, great for newer Porsches not so much for the air cooled cars

Most of us use 15w-50 or 15w-40, M1 15w-50 would be a great choice but there are others too.

Oil leaks due to synthetics is a canard left over from the very first days that syn was used in autos. At that time there were some issues that were quickly solved by reformulation to be compatible w/ the then existing seals, nothing has changed(except the significant reduction of ZDDP in many but not all oils) since the first syn products were reformulated.

Syn in transaxles is another matter entirely.