Hi Geoff, thank you very much for your kind answer.
Of course, I meant BMW328...
At the moment, oil pressure is about 1.5bar @ 3000rpm when hot, which seems a bit concerning.
The oil grade is 20w50.
There is no pressure warning light on the car and we haven't checked the electric manometer yet: that's what we'll do first with a mechanical one.
Do you know if the relief valve is adjustable on those engine?
Also, the car is equipped with an oil radiator and a non original oil filter on the pressure circuit, we also wonder if this couldn't be a problem...