Alarm - causes?

[Up The Creek]

Some advice would be welcome on a recent problem.

 

I recently acquired a Sea Otter with a 27HP Vetus engine. A fault has developed where a quite noisy buzzing (which I assume to be the alarm) comes from within the control panel as soon as I switch the engine on, and only disappears when the ignition is turned off.

 

A marine engineer came to look at it, but was unable to fathom the problem; his best guess was that there was a fault with the oil pressure sensor, which I don’t know how to check. He could find nothing seriously amiss - the oil warning light only glows momentarily, as normal, when I turn the engine on.

 

Any ideas? How to check the oil pressure sensor? Any other obvious possibilities?

 

Many thanks.

 

Bob

[John Williamson 1955]

Looking at the wiring diagram, it shows that if any of the warning lights are on, have a bad connection or a blown filament, this could cause the buzzer to sound continuously. There are 2 oil pressure switches, one for the engine and one for the gearbox. So, check that all the warning lights come on when you turn on the ignition, and that they all go out when the engine is running.

Edited April 8, 2015 by John Williamson 1955

[Iain_S]

The alarm should sound when the key is in run position without engine started. Ours on Gamebird (26' Sea Otter, Vetus M2.04) is fairly loud and high pitched, but I don't know what it would sound like if it only got a small voltage. Our warning lights, which sound the alarm, are oil pressure (sensor on the front of the engine), Temperature (sensor under thermostat housing) Exhaust temperature (sensor at rear of heat exchanger, not sure if this is connected/fitted in a keel cooled engine) and alternator. The temperature lights don't come on when the key is in the "run" position.

 

On our panel, the warning bulbs are in wired holders, so can be removed from the panel to check operation. There might be one glowing slightly when engine running, enough to set off alarm, but not bright enough to be visible through the coloured plastic lens.

 

It might be worth checking the multiplug connection at the back of the engine, as that can be the source of many strange electrical symptoms

 

Iain

[Up The Creek]

Thanks John and Iain. I'll do the checks you suggest.

 

The alarm when in "run' position is a very different (whistling) sound from the loud buzzing I've been getting once the engine starts, which I have simply assumed is an alarm. Does that make any sense?

 

Regards.

 

Bob

[Guest]

Thanks John and Iain. I'll do the checks you suggest.

 

The alarm when in "run' position is a very different (whistling) sound from the loud buzzing I've been getting once the engine starts, which I have simply assumed is an alarm. Does that make any sense?

 

Regards.

 

Bob

I am puzzled by the different tone that you get. Our slightly larger Vetus has the high pitched alarm that sounds when the ignition switch is turned to "run", but I have never been aware of a second alarm. There isn't some kind of extra alarm on the boat that is connected to the ignition switch such as a blige alarm? Just a thought.

Edited April 10, 2015 by Guest

[John Williamson 1955]

There are a couple of different control panels, and it's possible the boat builder has added something like a coolant level sensor an overtemperature alarm, which is independent of the engine maker's systems. I got the impression from your post that it was the same alarm sounding continuously. I suggest getting in touch with a Yanmar agent and giving them and accurate description of the problem.

[Sabcat]

Does the alarm stop if you rev the engine?

[Up The Creek]

Apologies for the delay in replying – I’ve been away from the boat for a few days. Ref. the suggestions and queries:

 

I doubt that the boat builder added an additional sensor or alarm, in that he personally came out to service the boat late last year and was also stuck for ideas.

 

Yes – the warning lights (oil and battery; no temperature) come on at ignition and then immediately go off.

 

If I increase the revs to over 2,000, the volume of the buzzing decreases significantly to become almost – but not totally - inaudible. Re. the confusion between the ‘whistle’ and the ‘buzz’, they do emanate from exactly the same ‘black box’ (Kingstate KPE-209), but the sounds are very different, and they are never audible simultaneously (ie the initial whistle is transformed into a buzz once the engine starts, and vice versa once I turn the engine off).

 

Hope that helps?!

 

Thanks.

 

Bob

[nicknorman]

Perhaps the buzz is the whistle sound but turned on and off rapidly. I wonder if you have a blown alternator diode, and that would tie in with the sound changing at higher revs. Is there any sense that the frequency, as well as the volume, of the buzz changes with Rpm? Are you sure the alternator warning light is not glowing slightly with the engine running? (Try it in the dark).

[Tony Brooks]

Perhaps the buzz is the whistle sound but turned on and off rapidly. I wonder if you have a blown alternator diode, and that would tie in with the sound changing at higher revs. Is there any sense that the frequency, as well as the volume, of the buzz changes with Rpm? Are you sure the alternator warning light is not glowing slightly with the engine running? (Try it in the dark).

 

I think that this is the first thing to check. We need to know the voltage when measured between the alternator warning lamp terminal and the main output (D+ to B+) when the engine is revving at 1500 rpm ish. That will not give any idea about blown negative diodes so it would help to know the charging voltage when the alternator is producing 10 amps or less when revving.

[Up The Creek]

Apologies again for tardy response to suggestions; I'm only at the boat once a week at present.

 

I think you may have put your finger on the problem. Yes, there is a sense that the frequency is changing/slowing as well as the volume; in a way, the sound seems to change from a loud, persistent 'buzz' to a quieter 'croaking snore' (hope that makes sense!) as the revs increase and, when I last tested, the noise disappeared completely for a split second or so at higher revs. And the alternator warning light is glowing slightly with the engine running.

 

I need to try what Tony suggests (although it may be beyond me!) but, in the meantime, does this sound like a potentially serious fault which needs urgent attention?

 

Thanks again for your advice.

 

Bob

[John Williamson 1955]

Sounds like a defective alternator. Either the regulator or more likely one of the rectifier diodes is faulty. It's a fairly cheap repair or exchange part in either case, done by your local auto electrical place. Before you take it off, check for loose connections and frayed wiring from the alternator to the warning light and ignition switch. Also. check the earth connections all round thoroughly.

[nicknorman]

Apologies again for tardy response to suggestions; I'm only at the boat once a week at present.

 

I think you may have put your finger on the problem. Yes, there is a sense that the frequency is changing/slowing as well as the volume; in a way, the sound seems to change from a loud, persistent 'buzz' to a quieter 'croaking snore' (hope that makes sense!) as the revs increase and, when I last tested, the noise disappeared completely for a split second or so at higher revs. And the alternator warning light is glowing slightly with the engine running.

 

I need to try what Tony suggests (although it may be beyond me!) but, in the meantime, does this sound like a potentially serious fault which needs urgent attention?

 

Thanks again for your advice.

 

Bob

Yes sounds like an alternator diode gone. The alternator is probably still working a bit, but well below its rated output. It isn't going to "blow up" but if it's not charging the batteries properly, they'll be the next thing to go.