Land Rover Repair: 2002 discovery low oil pressure, low oil pressure, main bearings

Question
I have a 4.0 discovery with low oil pressure, only 5lbs at idle.  The rod and main bearings have been changed, new oil pump installed, oil pan cleaned and engine flushed multiple times.  No change in oil pressure and no help from Rover. I'm just looking for fresh advice if you can.  Thanks

Answer
Depending upon the oil used, 5psi may be a normal warm oil pressure for your Rover.  With 0-40 synthetic oil we would only expect a few psi at idle.

Thicker oils like 20-50 will give higher pressure but there is no functional need for it and they will not perform as well in the motor.

Thin oils flow easier, saving gas.  They flow faster, aiding in engine cleaning.  The only tradeoff is that the lower pressure requires a stronger oil , which is one reason we now use Mobil 1 synthetics in our own service department.