Westerbeke M3-20B buzzer alarm goes off but oil pressure normal and engine cold - SailNet Community
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Old 05-19-2019 Thread Starter
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Westerbeke M3-20B buzzer alarm goes off but oil pressure normal and engine cold

The buzzer alarm on my Universal Westerbeke M3-20B is going off when it is not supposed to.

Normally, when I turn the key the alarm buzzer goes until I depress the preheat, at which point the preheat solenoid clicks, the fuel lift pump works, and the buzzer turns off. I then press the starter button as well, the engine starts and I let go of both buttons. The buzzer *should* come on momentarily until the oil pressure reaches 15psi (or is it 5psi?), and then the turns off again. The engine then continues to run normally at a fast idle until it is warmed up (cold engine stalls on a slow idle).

Everything appears to be the same now, except that the buzzer keeps going after engine start, constant and not pulsating.

The troubleshooting page suggests three things

1. Resistor shorting.
2. Fuel pump.
3. Oil pressure switch.

and offers diagnoses

1. Check resistor 1000 ohm. resistor found between preheat solenoid "I" terminal and ground.
2. Fuel pump coils shorting.
3. Oil pressure switch internal contacts not closing properly.

I don't know which of these is more likely, but I replaced the preheat solenoid only a week ago, after the old one broke it's mounting bracket and shorted out (due to my own clumsy inspection) on the block. The engine worked normally for one outing after that.

This blog post has a nice picture of the preheat solenoid
Replacing the glow plug solenoid
This page has all the technical manuals for my engine

I *think* I tested (1), above, and found there was not 1000ohms of resistance between the new preheat solenoid "I" terminal and ground (will check again), but I don't actually know where that resistor lives.

I see the 1k ohm resistor in the wiring schematic and diagrams, but not in the parts manual. What does it look like and where can I get a new one?

Comments and suggestions welcome.
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Old 05-19-2019
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Re: Westerbeke M3-20B buzzer alarm goes off but oil pressure normal and engine cold

The first think I would do is double and triple check anything I just did to the engine, if it was working prior to me touching it and not afterward. Connections, part numbers, anything else I disturbed, etc.

Is there any chance there is actually an oil pressure problem?

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Re: Westerbeke M3-20B buzzer alarm goes off but oil pressure normal and engine cold

Maybe the resistor is inside the solenoid unit.

One way to see if it's the oil pressure switch is to disconnect the wire on the oil pressure switch. If that stops the alarm, then it's either a bad switch or you really have a low oil pressure problem.

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Old 05-27-2019 Thread Starter
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Re: Westerbeke M3-20B buzzer alarm goes off but oil pressure normal and engine cold

I retested the resistance between I terminal of preheat solenoid and ground. It was about 300 Ohms (and not 1K), but more about this below.

I dug through the whole circuit for the preheat solenoid and disconnected it from all the things besides the phantom resistor. This includes unplugging it from the panel, the lift pump, and the oil pressure switch. I also checked that panel itself was not hiding the mysterious resistor. Testing again, the circuit had no connection to ground whatsoever. There is no resistor. It was not installed, likely because the resistor would be installer-supplied and is not a Westerbeke part.

No biggie, I sprayed some kind of electrical contact cleaner on everything I plugged back together, since things looked a little bit corroded, reassembled the wire harness, and left the oil pressure switch unplugged so that I could test whether it closes when the pressure rises.

After replugging, the resistance was down to about 20 Ohms (which seems much more plausible than 300 Ohms, now that I know this circuit connects to ground through the panel).

I had one little hiccup when the starter wouldn't activate, which I can probably put to faulty connections in this same circuit, so I plugged the oil pressure switch back in just in case that was causing the issue... When the starter finally did engage, lo behold the engine ran normally. The alarm buzzer didn't stay on.

I have to stare at the schematic a bit longer, but for now I can only conclude that cleaning circuits and un/replugging them improved the electrical connection enough to make things work properly!

At least I learned something...

edit: I checked the schematic again and now I don't understand how the alarm buzzer can possibly work correctly good night.

Last edited by driggers; 05-27-2019 at 02:34 AM.
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