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Rewards 06-17-2010 05:15 PM

Warning horn chirping
Here is a new one: my boat is powered by Yanmar 3GM30F. Motored hard (3400 rpm) for three hours, when pulling up to mooring the warning/starting horn started to chirp ever so slightly until motor was shut down and switch to off. That was 4 weeks ago; it has been getting worse since, now sounding at higher RPMs. I have checked temp; normal. Thermostat opening after warm up, plenty of water out with exhaust. Any ideas?

sailingdog 06-17-2010 05:41 PM

Have you checked the oil level? Have you checked the oil pressure? Motoring hard for THREE hours isn't really good for the engine.

Northeaster 06-17-2010 07:38 PM

Do you have dummy lights on the panel, for temp, oil pressure and charging?

It may be the charging - at low rpms, maybe there is a problem that the alternator is not charging. Easy to check. Test any 12v connection point, when the motor is reving highre, and make sure you are showing something like 13 volts +. Then lower rpms until the alarm sound and meter again. If you are only showing less than 13 volts, you are not charging.

At that point, you could troubleshoot alternator belt tension, or take off the alternator and take it t ohave tested.

donradclife 06-17-2010 08:01 PM

If you run at a faster idle for a while to let the engine internals cool down at bit, does the chirping still occur when you throttle back?? Probably low oil pressure, so its time to check the oil. If the dipstick is low, add some. If it is high, you may have a seal in the injection pump which is leaking diesel into the oil, cutting its viscosity. An oil change, perhaps with a higher weight oil, may solve the problem, but if it reoccurs you may need a mechanic.

Rewards 06-18-2010 12:30 AM

Oil level ok, charging at 14v. Hoping it is a bad sensor; think I will change out pressure sensor if I can find it. Also replace oil with synthetic; read testimony from race car driver that his engines ( gas ) run cooler with synthetic.

Note: there are three warning lights, none of which light up along with horn sounding.

eherlihy 06-18-2010 08:57 AM

Typically, the Yanmar engines do not have a full set of gauges.

That warning horn, actually a Sonalert, is like the "idiot light" on most modern dashboards. It means something is wrong.

Suggestions are either oil PRESSURE, or engine is over temperature. The easiest way to check pressure, is to first change the oil filter. Second, verify that the oil level is where it needs to be. Third, unscrew the pressure sender, and connect a pressure gauge where the sender on the engine block was. You should see over 5 psi, and less than 40 psi. The pressure should vary with engine speed.

For over temperature, first check the impeller on the raw water pump. Make sure that all the vanes are there, and not cracked. Second check the level and condition (specific gravity) of the engine coolant (freshwater & antifreeze). If the impeller checks out, and the coolant is OK, then I would check the engine with an infrared temperature gauge. Another member here, Maine Sail, has written an excellent overview of what to look for on a Westerbeake engine, but you can apply the same theory to your Yanmar. Here is a link to that writeup; Engine Temp Monitoring & Over Heating Baseline Assessment Photo Gallery by Compass Marine at

If these checks don't identify the problem, it is time to call a mechanic.

Good luck.

bjung 06-18-2010 09:34 AM

The GM series Yanmar has an operating RPM of 2900. Operating at 3400 RPM for 3 hrs. is a little much.
However, I have had a similiar issue with the warning horn, after I got pooped repeatedly, and submersed it. It kept chirping at very low volume, and intermittently for a few days, until it dried out. If everything ( temp/ press.) seems ok, then get a new beeper.
PSC 31

Faster 06-18-2010 11:17 AM


Originally Posted by Rewards (Post 614374)
Oil level ok, charging at 14v. Also replaced oil with synthetic; read testimony from race car driver that his engines ( gas ) run cooler with synthetic.

If this is an older engine converting to Synthetic oils may not be well-advised... there's been some discussion of this in previous threads.

Outside of that it does sound like a faulty sensor, or a partial short in the cct for the buzzer/horn.

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