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ctlow 06-09-2011 03:43 AM

Yanmar YM oil pressure alarm failure
The other day my oil pressure alarm failed. This is when starting and stopping the engine, the light should come on and the audible whistle activate.

I had this on a charter sailboat recently, too, and then it suddenly self-corrected.

Mine self-corrected too, by flipping the ignition switch from OFF to ON several times (engine not running!). It faltered at first, the light sputtering and the alarm sounding "dirty" and weak, and then suddenly they were both fine again.

I had been working around the engine and wondered if I had knocked a wire loose, but can't find one.

Is this something common or well-known, and easily user-serviceable?

I note that one can buy a replacement oil-pressure sensor, but don't know where it is on the engine itself, to even inspect it.

Thank you.


Yanmar 3YM20

SVCarolena 06-09-2011 08:50 AM

They way you describe it, it is most likely is a problem in the panel switch. I'd start there with a multimeter before going to the sender. Is is very uncommon for a sender to go bad, particularly on an interment basis like you describe. On the other hand, the panel and switch are exposed to the elements, so there could be corrosion inside.

casey1999 06-09-2011 03:18 PM

The wire harness have splice connectors- open them up and check for corrosion. Also some of these connectors at the panel. Spray with anti corrosion spray. Trace the wires from the panel to the oil pressure switch- the switch should be located around the oil filter- looks like a 1/2 pipe plug with a wire comming out the top. The water temp switch looks the same but located around the thermostat towards the top of the engine.

JimsCAL 06-09-2011 07:50 PM

If you remove the wire from the oil pressure switch and ground it, the alarm should sound (if the key is on). That would test the switch.

ctlow 06-11-2011 06:27 AM

All very helpful. Will investigate and hope to report back. Thanks to all.

saillife 07-06-2011 06:32 PM

Did you have any luck finding your problem? I too have an intermittent problem with the alarm. Mine seems to work once the engine is warm. I'm thinking it's the sender but, it could be heat improving a contact via expansion.

ctlow 07-07-2011 07:59 AM

Yanmar YM oil pressure alarm failure
Hello, saillife.

It simply started working again, and I have neglected to check into it. My bad. I had better have a look at the panel wiring - that alarm is a critical component.

Thanks for jogging my memory!


ctlow 07-27-2011 09:18 PM

Yanmar YM oil pressure alarm failure
The latest is that I jiggled everything I could find both on the engine block and on the back of the instrument panel, and nothing worked to restore the alarm.

The next day, however, and ever since, the alarm (and light) has worked. So if I take it in, it will all be working and they won't want to fiddle with it.


Where is the oil pressure sensor on the block, anyway? I can follow all sorts of wires - sort of - but can't convince myself which one is which and can't find a diagram of it. 3YM20.

Thank you.


BellaCoola 06-27-2013 04:54 PM

Re: Yanmar YM oil pressure alarm failure
Hi CTLOW---Disconnect wires one at a time and see which light does not go on when you turn switch before starting. Your oil sender will be low on your block, probably just near you fill line or above.
I'm trying to find fittings that go metric 10mm to 1/8 pipe standard so I can put an oil pressure guage on too alongside the sender as I have great pressure but sender goes off sometimes , even after changing !!. I know there was a post re this somewhere ????

mark2gmtrans 06-27-2013 05:07 PM

Re: Yanmar YM oil pressure alarm failure
The oil pressure sender is located on the engine above the oil filter. It is directly on the block and is slightly below and to the rear of the fuel pump. If you are standing in front of the engine, looking just above the oil filter you should see the wire going to it. If you find it is bad, it is a very simple fix and you should be able to do it in just a few minutes.

You will find the diagrams on page 12 of your owners

Send me a PM if you have further questions.


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