[C320-list] Oil Pressure warning

[Colin Evans]

 I have a 2000 model Yanmar 3GM30F.  When I start the engine the oil
pressure alarm and light come on as they are supposed to. However when the
boat has been motoring for 20 minutes or so and I put the throttle back to
idle the alarm sounds, but not a full alarm, sort of intermittent and the
light flickers.
I have changed the engine oil which was 6 months old, probably 40 hours,
thinking it may be getting too thin when hot.  I have run the engine in the
pen to working temperature at fast revs, then back to idle , but no alarm.
Any thoughts as to whether this is an electrical problem or do I have low
oil pressure.
 
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Regards
Colin Evans
#774  Lake Macquarie, Australia