First of all - I don't want to hijack this thread as an oil thread again....there are plenty of threads here about oils. I recommend to read on there.
@Duc Hunter
https://vpracingfuels.com/tech-talk-insider-articles/oil-viscosity-explained/
Quote:
What Does the W Stand for In Oil?
Exactly what does the W stand for in oil? Have you ever looked at a bottle of SAE 10W-40 or any other multi-grade engine oil and wondered about that? Contrary to what many people believe, the “W” does not stand for “weight” but “winter.”
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Later, they started formulating multi-grade oils like SAE 10W-30, 5W-30, 20W-50, and so on. When you read the viscosity grade on a quart of oil, the number to the left (before the “W”) is its winter rating. It represents oil viscosity measured at lower temperatures. The lower that number, the less the oil will thicken in cold winter weather.
The higher number to the right of the “W” represents oil viscosity at operating temperatures. Higher numbers reflect thicker oil viscosity. This gives the engine better protection for high-heat and high-load applications.
They test oil at a lower temperature to determine the first number (SAE 0W, 5W, 10W, etc.). They test it at a higher temperature to determine the second number (SAE 30, 40, 50, etc.).
For instance, SAE 5W-30 oil flows better at colder temperatures than 10W-40 oil. But, SAE 10W-40 oil is thicker. It provides better protection in warmer weather compared to SAE 5W-30.
Multi-viscosity engine oils don’t behave the same. It depends on the operating temperature. A multi-viscosity oil provides good flow in cold weather and dependable protection at operating temperatures in warm weather.
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You're right - these tables dated from the 70ies and 80ies. Modern oils can perform better than older ones.
Which oil you use in your car is result of several decisions: Personal preference, price, availability, others experiences and many more.
All I can say:
* The higher the ambient temps and the higher the heat stress on the engine are, the "thicker" the oil should be on high temps.
* I ran a high sophisticated all synthetic 10W60 (no brand known to me) from the workshop I got the car for the very first service. Result: Engine leaked that much that oil dropped on the heat exchangers and I thought the car will burn down now while driving it the first time on the autobahn and I smelled the oil fumes and seeing steam in back mirrors... Oil pressure not bad, but not as good as I wanted to see on idle and climbed up to barely 3bars max on hot wheather.
Switched to a petroleum based / non synthetic 20W50 (Liqui Moly Touring High tech). Result: Almost no dripping any more, reasonable higher oil pressure cold and warm.
Reasons: The petroleum based / non synthetic oils let the rubber sealings swell again by nature. Synthetic oils (no matter if full synthetic or not) doesn't. Why? It's because of their ester based oils. They don't let swell the sealings. Therefore they need additional ingredients to let the seals swell again. And that's the problem: Mostly modern oils have these ingredients, but not enough for aircooled engines like our beloved Porsche engines. Further reading e.g.
https://www.lube-media.com/wp-content/uploads/Lube-Tech-138-Sealing-compatibility-of-ester-base-oils.pdf
* Too less oil in the circuit let increase the engine oil temperature
* Make sure that the oil coolers are free of dust and not blocked
* Make sure that the thermostats open as designed
* Make sure that your ignition timing and advance&retard works as designed and being adjusted as Porsche recommended
* Make sure that the mixture is in spec as well, check it on a certified gas tester or at least with a lambda gauge both idle and cruising with AFR ~14,7, WOT & accelerating with AFR 12,5.
If all this been done, you're engine should run not much hotter than ~100°C / ~212°F on common street use. Racing / track day is another story of course.
Keep in mind that these oldfashioned aircooled Porsche were designed to be operated with the oils available of that time. I won't use either a 0W or 5W on an aircooled 911. At least 10W as Porsche originally specified above. As you guys mostly live in the US which is mostly warmer/hotter than e.g. Europe I recommend to go with at least a 15W40, 15W50, 20W50 or similar...But again: It's up to you.
And don't forget: These engines are 30 or 40 years old now and many of them still haven't been overhauled since. And most engine have far more higher mileage than most of odometers will tell...The higher the mileage of an engine is, the thicker the oil should be...this is valid for all engines, not only Porsches. And yes - it's true - a fresh overhauled engine is tight - with any oil! Question is how long this will last...
Finally and the very last task on the list to cool down an aircooled 911 - and only if all above tasks have been worked - you can install the 90110536102 intermediate pieces with reduced diameter. We had a discussion about them not long ago. I can confirm that these will bring up your oilpressure even on idle and cool down the engine in all operating conditions by at least 10-20°C / 20-30°F:
https://forums.pelicanparts.com/porsche-911-technical-forum/1141941-too-low-oil-pressure.html
Thomas