Engine alarm/sensor question

[Kyle Ewing]

My boat is a 1990, #1010 with M25XP engine.  While motoring through an anchorage yesterday after a day of sailing I heard what I thought was a slight engine whine, like a belt slipping.  After some investigation found it was coming from the engine instrument cluster.  It started very faintly at about 2000 RPMs and got louder as the engine speed increased, but never as loud as the alarm check when you turn the key on.  We anchored for about an hour.  On our way home it returned.  We motor sailed at 1500 RPMS for about 30 minutes while investigating further, then couldn't reproduce it.  Engine temperature remained at 160.  Engine performance and fluid levels were normal.

It seems electrical but the sound increase was linear with engine speed while it happened.  I haven't checked connections yet.

Has anyone experienced similar symptoms?  The only reference I found to alarm problems is related to loose wiring or bad sensors.  Could the tach wiring be somehow influencing the alarm circuit?

Is the oil pressure alarm an on/off switch?  It seems counterintuitive that oil pressure would drop as RPMs rise.


Thanks in advance for your thoughts!