advice on overheating Yanmar gm20 please

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dlwilkes

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the overheat alarm goes off intermittently after around 10 mins on tickover after starting other times it will run for couple of hours under load n o problems (seawater cooled)
I have done the following
1. replaced all pipework from inlet to exhaust
2. replaced impeller
3.hosed thro block in every direction
4.thermostat checked and working
5.decoked elbow
has anyone any suggestions ......does the block heat sensor ever play up???????
 
yes, frequently, the way to test is the same method of testing as the thermostat whilst using a multimeter on the terminals hold it in a pan of water and bring the heat up.
I have changed numerous ones.

i suggest you check the water flow by taking the water hose off the elbow and run the engine for a short time at tick over. It may pay to use some rydlym desaler in the block as well.


steve
 
Replace the sender unit in the block and clean all the electrical contacts and the alarm will cease! Almost certainly it is not actually overheating. Had similar issues with my 1GM and it took me nearly a season of worry to suss out it was electrical.
 
The only time the heat alarm has gone off on my Yanmar is when a kink developed in the raw water inlet pipe due to the inline strainer dropping a little in rough weather. This reduced the inflow sufficiently to cause rthe alarm to sound. Are you still getting water out the exhaust when the alarm sounds?
 
10 mins on tickover should hardly warm the engine.
Is the engine hot to touch when the alrm is going off? If not then definetly an electrical problem. The switch/sensor on the block is a simple on/off if you can disconnect the wire on the switch when the alarm is sounding and the engine does not feel hot around that area and the alarm ceases it sounds like you have a faulty temp sensor.
From what I can remember of the diagram when the engine cooling water gets to a certain temp the switch on the sensor activates and applies an earth on to the wire activating the buzzer and light. you could measure this with a multimeter if you have one.
 
Thanks for all the great guidance folks
Lots more things to try this week then,all seems to point to sender problems
(note for "SAWDOC" water still comes out when alarm goes off)
Thanks again I will post sucess soon (hopefully)
 
probably right Spyro,
but it took me a year to resolve! :(
pasted in link in case it helps another user if this thread shows up on search.
 
I just fired up my 30yr old yanmar 3gm20 yesterday after laying her up for the winter, and got an over temp alarm within 10-15 minutes of idling at around 1100 rpm. I did all the normal things - new impeller, pulled thermostat, checked intake rate, etc., but still get the alarm after 10 minutes or - running with NO thermostat at the moment.
I'm hoping it's just a bad sensor as the engine doesn't seem that hot, and I see a decent spray of water out of the exhaust, BUT, in the course of troubleshooting, I forgot to tighten a hose clamp on the intake side of the manifold and the hose popped off while running so I could clearly see a good volume of water coming from the sea water pump. Anyway, I also pulled the hose off the exhaust side of the manifold and tried blowing through it. I was able to blow some water out of the manifold, but it seems to require considerable lung power to even breathe air through it.
So, given the age of the engine I'm thinking the problem may be twofold - I wouldn't be surprised if there is considerable scale in the manifold, and I really don't want put much money into new parts... Does anyone have any experience or advice on a way to flush out the manifold or maybe other things I should look at? Thanks in advance - Paul
 
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