F50H low oil pressure alarm

[amaranth43]

I replaced on of my F50's this year, the engine is near new and has done about 300-400 hours so far. It is on a commercial fishing catamaran. The last couple of weeks I have been getting a low oil pressure alarm. It has done the same sequence each time:

Engine will start normally without incident at the start of the day.
I leave them to warm up at idle
As soon as I go into gear for first time the alarm sounds (or if I increase revs in neutral by depressing button)
I turn engine off, reset gauge (I have digital gauges), and restart engine.
The alarm will sound for a second time but not untll engine reaches 1200-1500rpm this time
I turn engine off, rest gauges and restart
Engine will then work normally for the rest of the day with no further alarms

Oil level is OK

I'll admit I've not done much more investigation, but just thought I'd post on here in case there is something obvious I am missing. Can get more info if required. I don't have pressure gauges, and the digital gauge isn't hooked up to display oil level, i just use dipstick. The weather has turned colder recently, not sure if this would have any impact. On the mornings the alarm has sounded it has been 0-5 centigrade (32-41F)

TIA

[99yam40]

Is the alarm actually low pressure?
Or out of spec?
might be too high due to being cold.
only way to tell is to monitor the pressure.
are you running the recommended oil for that temp range?

[fairdeal]

I think F50H is a "non-USA" model - but I suspect not much different than F50 models sold in the US

in which case, oil pressure is monitored by the ECM via a simple pressure switch:
the switch is "normally closed" - so there is electrical continuity to ground
but once oil pressure at the switch rises to ~10 PSI
the switch "opens"

Since the ECM has no pressure input other than that switch,
an "alarm" should only come from low oil pressure

(I can't recall any detail,
but there is some kind of "grace period" built into the ECM programming:
so that you don't get an alarm at key on, when of course there is zero pressure,
or in the first few seconds of running before the pressure builds)


The normal oil pressure at idle is probably ~25-30 PSI
Rising with RPM to a max of ~65 PSI as limited by the pressure relief valve.

I would personally start by swapping in a pressure gauge for the switch,
and see what pressure I'm getting at idle and above.

The pressure switch can easily be bench-tested while it is out.