What may the engine oil pressure indicator display up to when the engine is shut down?

The engine oil pressure indicator displays a potential residual pressure of up to 4 psi when the engine is shut down. This is due to the design of the oil system in the T-6A, which can retain some pressure even after the engine has stopped running. The residual pressure is a result of the oil remaining in the system components, and if the oil has not fully drained back into the sump, this can lead to a reading on the gauge.

Understanding this behavior is crucial for maintenance and inspection, as it helps to differentiate between normal readings and those that could indicate a problem with the oil system. The other values, while they may seem plausible, do not represent what is typically observed in a properly functioning engine when turned off. Therefore, the indication of up to 4 psi is important for pilots and maintenance technicians to recognize, as it can indicate the oil system's condition and inform decisions regarding engine health checks.