Troubleshooting engine alarm buzzer

[josrulz]

This is one of those little projects that wasn't super high on my list, but I knew I'd eventually get to. Well, I've gotten to it. When we bought our boat last year, the alarm buzzer wasn't working (gauges worked fine). The surveyor, and later my mechanic, both took the first guess that it was the buzzer itself.

So today I removed the alarm finally. I hooked it up directly to my battery, and it buzzed right away. Argh.

We have a Westerbeke W27. My assumption here is that when the key is on, but the engine is not running, that the alarm should be triggered by the oil pressure sender (since without running there's no oil pressure). Is this correct?

Is the oil pressure sender the likely culprit? Or should I look for a wiring issue of some sort.

Thanks!
-J

[erps]

I think the sender units are a switch to ground. No oil pressure, the switch to ground is closed and the buzzer buzzes. Develop oil pressure, the switch opens and the buzzing stops.

Remove the wire to the sender unit, turn the key on and then touch the wire to ground. It should start buzzing. If it does, I would suspect the sending unit, which can be confirmed with an ohm meter to see if it changes from closed to open when you start the motor.

[floatsome]

Check the wiring supplying the system to see if it was done correctly, or if a connection is undone (draw a schematic and follow all the wires visually). Senders can sometimes be faulty. If the alarm is for oil only and not temperature or raw water flow, then normally it is wired to buzz when the key is turned, and goes off quickly when the engine starts and oil pressure comes up. If the alarm is only for temperature, then it would not buzz unless engine temp is too high. Sometimes senders might not work if there is too much tape or thread sealant insultating the threads and preventing a good ground to the engine block where the sender screws in. Or corrosion might perhaps limit the ground connection at the threads.

[hellosailor]

"Sometimes senders might not work if there is too much tape or thread sealant insultating the threads and preventing a good ground "
I'd suggest there MUST NOT be any thread sealant or teflon tape on senders, only NeverSeize or a similar conductive paste.

Checking the schematic and confirming that the wiring matches it is job number one. Some senders are "alarm only" (on/off) and separate from the pressure sender. Others have two terminals, one for guage and a second for alarm, and all it takes it one loose or corroded wire to stop an alarm on that.

[josrulz]

Victory! Well, as is often the case, the problem was quite simple. I could tell you the whole story about reading the wiring diagrams, tracking down where the wires went, looking for the oil pressure sender and finding it obscured from view by the air cleaner (which I removed), all of which is true. Problem is, it's really not that great a story.

The fact is, the wire wasn't connected to the oil pressure sender! Well that'll do it!

Reconnected it, climbed back into the cockpit, turned the key on, and there you go...buzzer. Started the engine and confirmed shut-off, etc. and everything worked fine.

I was a little suspicious that it was disconnected--wondering if it had been done on purpose because the buzzer wouldn't shut off or something, but it appears to be fine. It might still have been on purpose because the buzzer is so annoying, but there's a good reason for that, so I'd rather it work.

Thanks for listening, and providing some suggestions.
Cheers,
J