oil pressure indication issue

[mobius maximus]

After the engine starts the oil pressure is spot on at 40psi. Pressure corresponds to throttle as it is moved. But eventually the pressure drops of to about 5-10psi and the gauge will occasionally flicker and even go in the negative range. Has a brand new sending unit and all new wiring. Any ideas? Thanks.

[maxpower220]

Check the ground to the battery, to the motor, and to the gauge. If you can, try to find a mechanical oil gauge and use it to determine actual pressure.

Cold oil will usually send a higher pressure until it heats up. So, part of this is in the "normal" range of operation. But negative indications is not.