What is the maximum oil pressure indicator reading displayed with the engine shut down?

When the engine is shut down, the maximum oil pressure indicator reading you might see is a function of the oil pressure sending unit calibration and the design of the oiling system within the engine.

Typically, a reading of 4 psi can represent the pressure in the oil lines when the engine is not running. This residual pressure is due to the oil remaining in the system after the engine has been switched off. That means there is still some pressure that can be detected by the sensor, but it would generally not be much higher than this value.

Higher readings, like 20 psi or 30 psi, would typically indicate oil pressure while the engine is running and actively pumping oil through the system. When the engine is off, the likelihood of seeing such high readings drops significantly as there's no active circulation occurring.

Thus, 4 psi as the maximum oil pressure indicator reading with the engine shut down is consistent with the expected behavior of the oil system and aligns with standard practices in engine diagnostics.