1.5ish bar is just fine and normal for a 40wt oil at hot idle. Changine oil/viscosity can have some effect, but within a small range and really not critical.

The oil's viscosity reduces by a factor of >10x when it is hot, which is why the pressure drops. Any car of any age with a real pressure gauge (i.e. not ford or others with dummified gauges) will show similar results.

It doesnt take a lot of extra RPMs to really boost idle pressure.

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