PLESE SEE LATER POST FOR BETTER MEASUREMENTS
Oil change and new filter fitted, some interesting conclusions. (Lexicon 20W50 no name no spec mineral, not the sort of stuff I would usually recommend, but at least I know what it is and it's cheap for testing, Mann filter)
Cold - 43 degree oil
1000 rpm - 3.4 bar
2000 rpm - 4.1 bar
3000 rpm - 4.4 bar - a bit lower than before, but the engine was certainly warm from residual heat
Warm - coolant needle off the white section, 55 degree oil
1000 rpm - 2.2 bar, needle no longer flickering
2000 rpm - 3.9 bar
3000 rpm - 4.1 bar - better than before, pressure more stable, perhaps benefitting from the new / better quality filter
Hot, coolant needle just below LED, fan running, the hottest I have ever seen it when running normally, oil at 80 degrees (photo taken a little earlier)
1000 rpm - 0.9 bar
2000 rpm - 1.8 bar
3000 rpm - 2.9 bar - a little higher pressure at the higher end
You can see that the oil temperature for this test in the photograph was 76.9 degrees. I really struggled to get it up to 80 degrees. What I was doing was allow the engine to idle at 1000 rpm, the oil temperature peaked at 65 degrees. Next stage was to increase the idle to 2000 rpm. This allowed the oil to achieve 75 degrees and then it started to cycle up and down a couple of degrees. At this point the fan was switching on and off its highest speed. I then moved the revs to 3000 rpm and after an increase the temperature started to fall again. The "hottest" running regime was around 2500 rpm and by holding the engine at that speed I managed to get up to 80.
I also noted the oil temperature at 1000 rpm as temperatures increased:
50 deg C - 2.4 bar
55 deg C - 2.2 bar
60 deg C - 1.7 bar
65 deg C - 1.4 bar
70 deg C - 1.1 bar
80 deg C - 0.9 bar
Conclusions - for now
I suspect the engine was already on 20W50 oil, the pressures were slightly better accepting that the readings were being taken about 5 degrees higher than before.
The coolant system is operating well, on the road it never gets as high as the LED needle so I suspect I have an 80 degree thermostat fitted
As revs go beyond 2500 rpm the additional oil flow through the bearings caused by faster oil pump rotation actually cools the engine rather than allows the additional heat being generated to increase the oil temperature
Engine revs dropped by about 70 rpm when the cooling fan kicked onto the high setting
The oil pressure at 80 degrees / 2000 rpm is a little below VW spec, but not catastropically
Next course of action is to get a black / 1.4 bar "high" pressure switch, fit than and take measurements again but from the low oil pressure switch location
Perhaps a sweepstake should be set up to predict what the oil pressure will be at that location