On start up I don't put in the impeller. I hang it from the pump and advise customer to install it before the boat hits the water. My last 2 boats that the engines were installed didn't go into service for almost 2 years after I delivered them.

Need to eliminate known good components... filter, air cooler, injection pump and timing, injectors, even compression, fuel delivery, hull condition, props, etc. Old fashioned trouble shooting. That is a dying art. No plugging in a computer for this one.

I have customers out there that are over 5,000 hours and still running fine. The environment where it's run and how it's taken care of usually governs how long it lasts.

Check oil level. Check oil being thinned out by injection problems. Check with mechanical oil guage to eliminate electrical problems.

This was a customers that I rebuilt. I have others used and newly rebuilt.