Having issues with high pressure (15 psi with key on but engine not running, 50 psi at idle, and 75-80 psi at full throttle) on a 5.7 Indmar with about 300 hrs. The idle and throttle psi's were with warm engine (160 F). Running Mobil 1 filter and Rotella 15W40 oil (yes, the diesel version). Changed sending unit (both old and new were 240 ohm without engine running, but changing was the easiest/quickest resolution attempt) and still have same issue.

1. Should the dashboard gauge read 15 psi without it being turned over? This is the case even with the oil cap and dip stick removed. If the gauge
should read 0 psi when gauges on but engine not, can the gauge be reset/fixed?
2. What should I look at next?
3. Should I even be concerned? Lots of forum chatter regarding concerns with low pressure, but not many seem to be overly concerned with high
pressure.

Appreciate everyone's review/feedback.