An oil pressure warning came up. Just after driving for a while in slow traffic, warm outside, AC on. I shut down that car form about 15 mins and after starting again and idling the warning showed up. t may have been briefly under 1.5 bar but still looks like 2 bar to me.

This displayed warning "Oil Pressure Insufficient" is triggered by the sensor switch part while the oil pressure gauge is driven by the variable sensor - so it would seem your sensor has a pressure switch that is set to a higher pressure than most... Mine triggers around 1.0-1.5Bar (closer to 1 bar I think) and that seems about typical.

It is in the body of the sender unit- one pin is for earth, one pin for analogue output and the other pin for the switched output on your type of sender

Sounds like either a faulty sending unit or bad wiring in the loom. Check the 14pin connector at the ext power post. That is where the sensor is hooked up to the loom and where the dash gets the signal from. The dash converts analog to digital for pressure but the switch is a simple 'switch". 

Using a thicker oil will help a little if all electrical things check out fine.

If it is hot, stick the Castrol 10W60 TWS for M-Engines in and forget about the problems. The race car engine will still have just about 2bar at idle after a 50min session on track, with water temp on the last white line of the gauge.

The Porsche guys I talked to at Parade in Monterey were emphatic that the new oils (both 20w50 and 10w60) are for the air-cooled engines only. The Porsche Classic web pages specify the 20w50 for 356/914 and early 911, and the 10w60 for 911 from 3.0L and up.

The issue with the early air-cooled engines is flat tappets (i.e. zinc) and high oil temps (good hi-temp viscosity). So why would that not also be good for our engines in high temps? The cST viscosity for the Torco SR1 10w60 is quite a bit higher at 23.23, which may suit hotter climates better than a 20w50 or may be too high-- I don't know. The only other 10w60 sample I have looked at is the Liqui-Moly with a cST viscosity of 21.85. Zinc for this oil was higher than the 20w50, 1015 versus 818 ppm, while Liqui-Moly was 824.

This is simply raw data, I am not making any recommendations here. As noted above, the Porsche oils are intended for their air-cooled engines. The biggest issue there is high oil temps, which is something that our engines share in warmer climes at least. I don't know of any other oil characteristics that would disqualify them for use in our engines.

I've been told by the most reputable 997 engine builder that in order to properly protect the motor and valve train in both the m96/m97 motors and the classic Porsche motors (993, 928, etc), that Zinc and Phosphorus levels need to be from 1,000-1,200 ppm.