Yanmar 3GM overheating alarm....

[Crazy-Diamond]

I’m motoring along the Essex coast this morning, very little wind. My cooling alarm went off on the engine panel. Initial checks show nothing wrong. The strainer is not blocked, with water flowing through, there is water coming out of the exhaust just fine. My gut feel, when opening the engine bay, is that the engine is running perfectly normally, and did not smell hot. I’m a bit baffled.
Could it be the warm weather? The sea temperature is quite warm (22 degrees). I had been motoring for approx 3hrs at 2500rpm.
little bit worrying as I’ll be needing the engine to get back to the shore!
Any thoughts?
I’m letting it cool and then I will open the heat exchanger pressure cap to look for any problem. The level of water in the expansion tank is normal
Thanks,
Giles

 

[Crazy-Diamond]

Well, I opened the pressure cap on the heat exchanger. The coolant is full, and I could put my finger into it just fine, hot, but not scalding.
Faulty sensor?

 

[jiris]

Well, I opened the pressure cap on the heat exchanger. The coolant is full, and I could put my finger into it just fine, hot, but not scalding.
Faulty sensor?

You are probably on the right track. It may be the sensor itself or the wire to it is shorted somewhere on the engine block. The sensor does exactly that when temperature goes too high.

 

[Slowboat35]

Without wishing to teach you egg-sucking, be very careful opening a pressure cap when hot especially if suspecting an overheat- if it is overheating you risk a faceful of boiling water!
Digital no-contact thermometers are cheap, not a bad use of £15 just in case, plus has other uses.

 

[Crazy-Diamond]

After some more diagnosis I found the culprit, the main belt had broken.

 

[Crazy-Diamond]

...cont. I had not even thought to check this at first, lesson leant, and once spotted I had a replacement on in no time.

 

[peteK]

The battery wouldnt of been charging,surprised you didnt notice it.

 

[jiris]

View attachment 96260After some more diagnosis I found the culprit, the main belt had broken.

Besides of the battery not charging, It just doesn't fit to the part where you were able to open the water cap safely and feel the water not too hot by your hand. While I don't have any doubts about a broken belt would cause overheating , the rest is weird.

 

[awol]

Besides of the battery not charging, It just doesn't fit to the part where you were able to open the water cap safely and feel the water not too hot by your hand. While I don't have any doubts about a broken belt would cause overheating , the rest is weird.

No coolant circulation through the engine or heat exchanger - conduction and convection only. Not surprising alarm is going but tank is only warm.

 

[Crazy-Diamond]

The coolant in the heat exchanger would have been cooled by the raw water, and I waited about 45 mins before opening it.
I should have seen the alternator alarm light, but was distracted by fearing the warning was my saildrive gaiter alarm, and then finding I could not understand the icons on the warning lights. I shall be adding clear labels above each light.