The owner's manual will tell you that at idle, in gear, oil pressure needs to be at least 0.3 bar. Mine tended to be about 0.5 in really hot weather, AC on, in stop-and-go traffic, with conventional oil. Now with Mobil 1 15W-50 it's always above 1 bar under those conditions.

As long as the pressure rises to 3 bar once RPMs get to be above about 1500-1800, you're OK.

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Steve
'93 400E