Overheat buzzer buzzing continuously - Yanmar 3HM35F

[SailMaster]

Upon starting when cold, our overheat buzzer or the sensor is buzzing constantly with the switch on. It continues to buzz as the engine heats up. I am having trouble figuring out which is the temp sensor to disconnect to stop this. I am about to do a 4 hour run and do not want to listen to this the entire time.

I tried disconnecting the sensor at the front of the engine near the thermostat. That does not shut it down. Any thoughts?

 

[jviss]

1. Are you certain it's the overheat buzzer, not the oil pressure buzzer?
2. If disconnecting the sensor doesn't stop the buzzer, and you're sure you've disconnected the correct sensor, then there's likely a short to ground in the sensor wire to the buzzer. Try disconnecting and measuring the wire's continuity to ground. If it's not open, i.e., high resistnce to ground, then there's a short.

 

[SailMaster]

1. Are you certain it's the overheat buzzer, not the oil pressure buzzer?

Yes I am certain. In fact we do not have an oil pressure buzzer. I need to install one when I get the chance.

 

[JoeWhite]

I had that problem. It was due to excessive engine vibration which would shake and ground the high water temperature sensor by-metal strip inside the sensor.
The excessive vibration was due to cracked alternator bracket, which broke eventually on a long engine run.

 

[Benny17441]

It could be a short in the wiring. The wiring harness from the control panel to the engine compartment is usually routed through some fiberglass bends around the hull. In older boats with years of hull flexing the insulation of this harness can be chafed and short circuits occur with odd results from the warning lamps and the buzzer. A visual inspection of the harness around the bends can usually reveal the spot where the insulation has been damaged. If you disconnect all sensors and the buzzer is still going there is a strong indication of a short circuit somewhere.

 

[jviss]

It could be a short in the wiring. The wiring harness from the control panel to the engine compartment is usually routed through some fiberglass bends around the hull. In older boats with years of hull flexing the insulation of this harness can be chafed and short circuits occur with odd results from the warning lamps and the buzzer. A visual inspection of the harness around the bends can usually reveal the spot where the insulation has been damaged. If you disconnect all sensors and the buzzer is still going there is a strong indication of a short circuit somewhere.

Benny, you have a habit of repeating things folks have already said. See my reply #2.

 

[kloudie1]

Attached is of a 3GMF, which is very similar to the 3HM . The red circle is around the temperature switch , on the thermostat housing. That wire should be a white with blue stripe.. You may have some kind of interconnect with the oil pressure wiring that is causing the annoyance. That wire is yellow with white and will be in the vicinity of the oil filter .. If you do not have an oil pressure buzzer, someone may have disconnected it and it may have come adrift and shorted with the temperature circuit. I have attached a wiring diagram showing the buzzer and what drives it.

 

[Benny17441]

Benny, you have a habit of repeating things folks have already said. See my reply #2.

I was letting Sailmaster know about the tendency for chaffing of the wiring harness in older boats and that it can be rather easily located by a visual inspection in the areas where it goes around the bends. I'll let him decide whether my post was useful or not.

 

[jviss]

I was letting Sailmaster know about the tendency for chaffing of the wiring harness in older boats and that it can be rather easily located by a visual inspection in the areas where it goes around the bends. I'll let him decide whether my post was useful or not.

Fair enough.