Humor me with your whine theories, V8-380-CD

[Toddavid]

When running cold, I‘ve been hearing a somewhat faint mid-octave whine this season, only happens when under load.

Not as high pitched as fuel pump (plenty of direct experience with that issue).

Doesn‘t change in pitch, slightly louder at various higher rpms, not there at idle.

After heat soaking on the hook for a few hours, the whine is a lot quieter, barely noticeable.

Been going on for the last 40-50 hrs, hasn’t gotten worse.

Stethoscope on various engine components hasn’t narrowed it down, but I haven’t been able to check underway and under load (no one else to drive the boat).

Open to ideas.

Thanks.

 

[Grub54891]

Sounds like a vacuum leak.

 

[ESGWheel]

I assume your engine is MPI since you mention fuel pump whine, thus my guess: Fuel Pressure Regulator in the fuel rail.

Also one of those mechanics stethoscope with an air horn (as well as a rod) is great for initially localizing the noise and then go from there with the rod (Link.) once you find someone to drive the boat….