You may want to consider putting in a mechanical sending unit and an aftermarket gauge. I was anoyed and concerned with the "non-fluctuating" oil pressure gauge so that is what I did. 03ramit1 is correct, the stock gauge is almost worthless.
The following is directly from my service manual...
Engine Oil Pressure Message - The instrument cluster circuitry restricts the oil pressure gauge needle operation in order to provide readings that are consistent with customer expectations. Each time the cluster receives a message from the PCM or ECM indicating the engine oil pressure is above about 41 kPa (6 psi) the cluster holds the gauge needle at a point near the middle increment within the normal range on the gauge scale.
Engine Oil Pressure Low Message - Each time the cluster receives a message from the PCM or ECM indicating the engine oil pressure is below about 41 kPa (6 psi), the gauge needle is moved to the graduation at the far left end of the gauge scale, the check gauges indicator is illuminated, and a single chime tone is generated. The gauge needle remains at the left end of the gauge scale and the check gauges indicator remains illuminated until the cluster receives a message from the PCM or ECM indicating that the engine oil pressure is above about 41 kPa (6 psi), or until the ignition switch is turned
to the Off position, whichever occurs first. The cluster will only turn the check gauges indicator on in response to an engine oil pressure low message if the engine speed message is greater than zero.
My Autometer mechanical full sweep gauge shows 55 psi at startup and while warming up, never any less than 35 at idle and 75 psi at 5,600 rpms. That is good oil pressure since you really only need about 10 psi per 1,000 rpms.
