Low oil pressure alarm / schematic

northshore

Well-Known Member
Jan 17, 2011
2,072
Cleveland, OH
Boat Info
1989 340 Sundancer
Raymarine E90W Radar/Chartplotter
Engines
Twin 454 Mercruiser 340's
Chasing an intermittent low oil pressure alarm (stbd only) when the key is set to the on position (with engine off).
The starboard low pressure indicator on the system monitor panel lights brightly without fail but the warning buzzer may or may not go off. More often then not, it will not alarm.

I have shorted the oil pressure switch (with electrical connection still attached) to ground and this did not set the alarm off. Additionally, hoping it was a bad connection behind the switch/breaker panels, I removed both panels and shook and tugged on the harnesses with no change.

The port side alarm works fine everytime.

I had a look at the schematics that Sea Ray provided me some years back but the schematic does not match what is installed on my boat (I believe the schem was from an earlier model) as it has 3 individual alarms (port, stbd and genny) whereas mine only has 1 for all three.

If anyone has a more accurate schematic or insight as to what might be causing this or a next troubleshooting step, I'd appreciate it.

-Mike
 
Chasing an intermittent low oil pressure alarm (stbd only) when the key is set to the on position (with engine off). ...

I have shorted the oil pressure switch (with electrical connection still attached) to ground and this did not set the alarm off. ...

If anyone has a more accurate schematic or insight as to what might be causing this or a next troubleshooting step, I'd appreciate it.

-Mike

Hi Mike, I had a 340 of that vintage some years ago. I don't have the schematic but I can tell you the low oil pressure alarm is a switch right next to the oil pressure sender and it is activated by shorting to ground. So you can try removing and isolating that connection and see if it is bad wiring going to the helm.
 
Thanks Orlando
I grounded out that pressure switch with no change.
I think my next task is to trace that wire back to the alarm system under the helm.
 
... I grounded out that pressure switch with no change.
....

Yes, that WILL activate the alarm. You need to disconnect the wire from the switch and see if it goes away. That will tell if it is the wiring or the switch. That's assuming you don't have low oil pressure that it.
 
That should do it, but alas...

So when you say no change, your looking for the alarm to turn on or off? I am unsure what your looking for, at first it sounded like it was going off randomly without low oil pressure. But to go further with this the left side panel at the helm should have a couple of terminal blocks and there you will find the system monitor inputs. It's easier to trace it from the helm panel then from the engine. They were once marked with a plastic covered paper with the names of each next to the terminal block.

The sounder is a separate issue. That is probably defective especially if it is original. Easy enough to replace with a new one. Just search Piezo buzzer on amazon.

There is some information in the owners manual around pg31: https://owners-resources.searayweb.com/owners-manuals-files/1989_340 Express Cruiser_1989_340_Sundancer_Express_Cruiser.pdf

Also this may help, it's from a new boat but it's the same sys monitor: https://owners-resources.searayweb.com/owners-manuals-files/Owners Manual 1999 340 SUNDANCER.pdf
 
Hey Orlando

It's an 'engine off' issue. More times than not, I do not have the expected alarm buzzer when I turn the key switch to the on position but the LED on the systems monitor always lights as expected. My great hope was that the oil pressure switch was bad and grounding it would have immediately set off the horn/alarm but it did not do so.
I know the buzzer its self is good as the port side always alarms as it should and port and starboard utilize the same buzzer.
I think I'm getting enough current to light the LED but most times not enough to sound the alarm buzzer.
Crap connection somewhere....

So yes, I'm going on the hunt for the terminal block you speak of next weekend.
Thanks for the links - the newer 340 has exactly what I was looking for.
 
Hey Orlando

It's an 'engine off' issue. More times than not, I do not have the expected alarm buzzer when I turn the key switch to the on position but the LED on the systems monitor always lights as expected. My great hope was that the oil pressure switch was bad and grounding it would have immediately set off the horn/alarm but it did not do so.
I know the buzzer its self is good as the port side always alarms as it should and port and starboard utilize the same buzzer.
I think I'm getting enough current to light the LED but most times not enough to sound the horn most of the time.
Crap connection somewhere....

So yes, I'm going on the hunt for the terminal block you speak of next weekend.
Thanks for the links - the newer 340 has exactly what I was looking for.

If the led is on then the buzzer should sound. There is a timing circuit on the board to stop the buzzer from sounding when when power is first applied to the engine and only after a long period if time does it start buzzing. I think something like 120 sec? Might be longer I forget, sorry. But if you leave the key on for an extended period of time it will start sounding or should. If that doesn't happen then it's the system monitor board itself.

Take a look at your sys mon board there should be a ribbon cable that leads to a terminal block, or possibly to another board. If it goes to the secondary board then the problem is on that board. Those are tough to find if at all.
 
The port side alarm comes up after roughly 5 seconds.
I'll do some digging this weekend.
I appreciate the help Orlando!
 
Ok finally got back to the boat today - and it works just fine.....:confused:

And for what it's worth the alarm comes on instantly - both sides.
 

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