The 0.7 bar minimum is something I got off the forum here.
I'd look at you oil pressure sensor if your meter doesn't top out. Check the connections and make sure you have good contact. While we may argue at what the idle pressure should be, it should always be at 3 bar when your foot is on the accelerator.
For the older engines (worn), Valvoline has an oil called 'Max-Life' that is supposed to work well.
'05 E320 CDI - 86,000 miles
'86 300SDL - 360,000 miles
'85 300SD - 150,000 miles (sold)
'89 190D - 120,000 miles (sold)
'85 300SD - 317,000 miles (sold)
'98 ML320 - 270,000 miles (sold)
'75 300D - 170,000 miles (sold)
'83 Harley Davidson FLTC (Broken again) :-(
'61 Plymouth Valiant - 60k mikes
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