Almost all oil pressure problems are low oil pressure (indication).
I have the opposite namely a high oil pressure (indication), when the engine is idling the needle of the dash gauge goes completely to the rightside past the 7 mark.
I have done the following in order to try to solve the problem:
Replaced the oil pressure sender however it didn't solve the problem
Measured the oil pressure with a gauge. (T junction made at the oilfeed line coupling at the turbo). Measured 4.5 bar engine idling 1200 RPM, measured 5.0 bar at 3000 RPM (engine / oil was cold), indication in the dash was 7+
Checked dash gauge indication. removed the "WN" (White - Brown stripe) wire from the sensor and connected a potentiometer to it. See table below. No obvious misreadings / indications. The gauge indications in relation with the resistor values match (almost) the 0 - 184 Ohm curve of a 0 - 10 bar VDO pressure sender. (end point is different).
Resistor value (Ohm)
0 - Red
1st white stripe
2nd white stripe
3rd white stripe
4th white stripe
5th white stripe
6th white stripe - 7
Measured the resistance between the sender housing and the engine block, almost 0 Ohms (0.1 Ohm), so no problem there
Disconnected the Oil pressure warning switch wire and started the engine, no joy needle goes to the max.
Some other things:
The Oil in use is Castrol Edge 10W 60, engine filled in may 2019 from unopened/sealed "containers", these have been sitting on the shelf for about 4 years before being used.
The standard oilcooler flange between the oilfilter and the oilpumphousing is replaced by a thermostatic version (Mocal IIRC).
I saw the the dash gauge indication drop 1 or 2 times during a testdrive on the highway, everything nice and warm. After a very short time the needle went into the corner again.
If anybody got some ideas / info etc for solving the problem I would be more than gratefull.