3YM30 temperature alarm

[DaveRo]

(Janneau SO35 - in Greece)

I am getting a false high-temperature alarm. At low revs the warning light flickers and the beeper warbles. At normal revs both are on full.

Anybody had this? Faulty sensor or engine control electronics? Why the warble at low revs? I would expect if the temp were really too high (coolant hotter than 95degC according to the manual) both light and beeper would be on full.

Pulling the wire off the sensor makes no difference. Only way to shut it up is to pull the plug on all the alarms on the engine panel.

Anyone know of a supplier of Yanmar parts in Greece (Athens preferably) who will ship to the islands?

Any advice appreciated. Can't google or search much - limited internet connection here between Skyros and Psara. Maybe there's a Yanmar forum?.

Dave
s/ Vigdis

 

[mapron]

A temp. gauge measures the resistance of the thermistor in the sensor and indicates this as a temperature. The hotter the sensor, the lower the resistance. If your gauge is reading when it shouldn't this could be the result of the sensing lead shorting to earth. But - you said that disconnecting the lead (at the gauge?) made no difference so this is odd.
Use a voltmeter to check the +12v supply to the gauge, also check that the neg earth is sound. If these are ok then check the gauge.
If the gauge is working correctly, when you disconnect the sensing line which goes to the sending unit at the back, it should go to its lowest reading.
If you connect a jumper from the sensing line terminal on the gauge to a good engine ground, the temp gauge should go to its highest reading. If it doesn't I would suspect that the gauge is faulty.
To check the sensing wire, short the sensing line to the engine block.
The temp gauge should go to its highest reading.
If it doesn't this indicates a fault in this lead.
Hope this helps.

 

[jwilson]

(Janneau SO35 - in Greece)

I am getting a false high-temperature alarm. At low revs the warning light flickers and the beeper warbles. At normal revs both are on full.

Anybody had this? Faulty sensor or engine control electronics? Why the warble at low revs? I would expect if the temp were really too high (coolant hotter than 95degC according to the manual) both light and beeper would be on full.

Pulling the wire off the sensor makes no difference. Only way to shut it up is to pull the plug on all the alarms on the engine panel.

Anyone know of a supplier of Yanmar parts in Greece (Athens preferably) who will ship to the islands?

Any advice appreciated. Can't google or search much - limited internet connection here between Skyros and Psara. Maybe there's a Yanmar forum?.

Dave
s/ Vigdis

I have had tow temperature alarm problems ona 3YM30. The first was genuine overheating, the first 5,000 or so of these engines built were undercooled, cured by fitting a bigger heat exchanger under warranty. On the original heat exchanger 10-15 minutes of over 3,000 rpm would overheat the engine. I found this early as I like to give diesels 10-20 minute bursts of full or near full power occasionally to counter lots of low-rev running.

The second (after new heat exchanger) proved to be intermittent false alarms through the insulation on the sensor cable rubbing against the engine block as it vibrated, wearing through the insulation, and shorting out. Now re-insulated and cable tied away from block.

 

[DaveRo]

Thanks for those useful replies. I will carry out some tests and report back.

Yes - I pulled the wire off what looks like the sensor - it's just below the top hose from heat exchanger to 'fresh-water' pump - and it did not stop the alarm. That suggests that it's not a faulty sensor.

Mine is a newer engine than the ones with heat-exchanger problems.

What puzzles me is that at low revs the lamp and buzzer only flicker/warbles rather than being full on. Is it designed to do that? Or is it perhaps related to alternator output.?

The sensor wire is sheathed and doesn't seem to be shorting but it disappears under the engine - I assume ther's a control box down there somewhere.

Off to Chios today so I may not respond for a few days.

Dave

 

[DaveRo]

... but no wind so time to do simple tests before we go.

Voltage at sensor on tickover - much less than 12V. Difficult to measure accurately but about 3V. If I rev up the engine the voltage goes to near zero.

If, on tickover, I short the sensor wire to the engine, the alarm comes on full.

Anybody know where to look for the alarm conrol box on a SO35 - what does it look like?

 

[DaveRo]

For the record: the alarms logic module is bolted to the engine at the rear/bottom/port side. I can see the connectors there for the sensors and lamps. But I can't get at it - I may even have to cut a hatch in the heads wall! (Fire safety implcations? Metal hatch cover?)

The temperature alarm has now failed OFF - which is better because it means that means the other alarms can remain connected. It doesn't even light when you turn the key.