> Some oils maintain their grade better than others, but when an engine needs
> new main bearings, it needs new main bearings.  If I saw 7-10 psi of oil
> pressure in a running engine, I would hesitate to go to the end of the driveway.

7psi at idle, particularly when cold, is definitely a sign of Trouble
Ahead. At temperature, though, 10psi seems to be about average for
older WBX engines. The low pressure oil sensor trips at .3bar, which
is 4.35psi. It may be an ill omen of future failure, but 7psi is still
well within the limits of "functionality".
 
> By the way, isn't the oil pressure switch setpoint 0.9 Bar?

The high pressure sensor is .9bar (13psi). At highway speed (4000rpm)
a pressure of 20psi is a little weak, but by most accounts I've read
bearing death isn't imminent until it can't manage 15-17psi at
4000rpm. The old original engine in my van with probably 180,000 miles
on it only gave me a couple thousand miles before a rotted head stud
snapped, but oil pressure had remained steady at 10psi idle, 20-21psi
at 4000 for those miles. I suspect that had the head stud not gone,
and had the rotten, leaky head gaskets held, I probably could have
safely squeezed another 10-20,000 miles out of it.