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Old 06-07-2019, 13:21   #1
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Yanmar 1GM Overtemp Alarm / Thermostat

Yanmar 1GM. Overtemp alarm. Replaced impeller. Still alarm. I have manual.

Thermostat: my experience with cars is thermostats "fail open" - so if a thermostat fails, the car is slow to reach temperature (because thermostat is wide open) - but a bad thermostat generally won't cause overheating.

What about these Yanmars ? I understand the thermostat directs water either into engine or bypassing it. If thermstat fails, does it send all the water into engine ? Or all bypassing ?

Obviously I need to look at obstructions, sending unit, and other parts of system.

Thanks !
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Old 06-07-2019, 18:51   #2
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Yanmar 1GM Overtemp Alarm / Thermostat

Your car experience will carry over here as well.
First thing Iíd do is buy an inexpensive IR thermometer and measure the thermostat Neck when the alarm goes off or keep checking before to see if you really have an overheat or just a bad switch.
If itís a real overheat, first and easiest is to check the thermostat, it should begin to open at set temp, full open 15 or so degrees higher, if thermostat is good Iíd move onto heat exchanger and from there the exhaust manifold.

Sometimes however you can have a worm pump cover and it not pump much water.

Thermostat usually blocks water flow, but there is a type that is longer than normal and has a large washer on the bottom that may bypass.

This may help
http://www.stant.com/index.php/engli...s-thermostats/
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Old 06-07-2019, 18:58   #3
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Yanmar 1GM Overtemp Alarm / Thermostat

Last thing, I believe on my Yanmar anyway the overheat and low oil pressure are the same alarm sound, you have to look at the light to determine which it is.
I donít know about yours
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Old 06-07-2019, 19:10   #4
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Re: Yanmar 1GM Overtemp Alarm / Thermostat

Quote:
Originally Posted by Delawaredave View Post
Yanmar 1GM. Overtemp alarm. Replaced impeller. Still alarm. I have manual.

Thermostat: my experience with cars is thermostats "fail open" - so if a thermostat fails, the car is slow to reach temperature (because thermostat is wide open) - but a bad thermostat generally won't cause overheating.

What about these Yanmars ? I understand the thermostat directs water either into engine or bypassing it. If thermstat fails, does it send all the water into engine ? Or all bypassing ?

Obviously I need to look at obstructions, sending unit, and other parts of system.

Thanks !
Welcome aboard D-dave.
In the closed (cold) position, the IGM directs all the flow to the exhaust mixing point bypass the engine. In the open (hot) position, it directs all the flow though the engine before exiting it to the exhaust mixing point.

Usually fails in the closed (cold) position thus causing overheating but I have had one fail in the fully open position. In this case no alarm, just a engine rising way to cold.
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Old 06-07-2019, 19:11   #5
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Re: Yanmar 1GM Overtemp Alarm / Thermostat

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Originally Posted by a64pilot View Post
Last thing, I believe on my Yanmar anyway the overheat and low oil pressure are the same alarm sound, you have to look at the light to determine which it is.
I donít know about yours
Correct for the xGM series
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Old 06-07-2019, 19:49   #6
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Re: Yanmar 1GM Overtemp Alarm / Thermostat

Remove the thermostat and then run the engine. No alarm? You've got a bad thermostat (replace as necessary). If not, check your salt water intake thru-hull strainer on the outside of the boat. Barnacle and sea growth will prevent proper salt water suction (and add wear and tear on the new impeller you just installed). The water temp sensor may have failed as well (should not come on when you turn the key on and start the engine....if it does? Bad sensor).

In normal operation the 1GM never really gets too hot to touch. If it does, then the three things which I have listed above are the most likely culprits. Good Luck!
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Old 06-07-2019, 20:05   #7
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Re: Yanmar 1GM Overtemp Alarm / Thermostat

I guess you've already looked to confirm acceptable water flow out the exhaust?

You can check the thermostat by heating it in a saucepan of water with a thermometer to see when it opens. If you're still unsure, reassemble the cooling system but leave the thermostat out, run up close to operating temperature, then close the bypass line (use a small vicegrips to squeeze the hose). This way you are guaranteed full flow through the engine, and now you can run it hard to see if the alarm still goes off. If you just remove the 'stat without constricting the bypass almost all the water will go through the bypass and the engine will quickly overheat.

I had a problem years ago that drove me nuts - I checked and replaced impeller, 'stat and hoses, and soaked the passages in vinegar, but still got an alarm after about 20 min at 3/4 revs. I finally rodded the CW seacock and thru hull with a very long screwdriver, and found in there a long hard piece of marine growth the like of which I'd never seen before. I put the old impeller and 'stat back in just to check: good as gold, except for about a hundred bucks and 20 hours of my time down the drain.

Cheers, Graeme
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Old 06-07-2019, 23:09   #8
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Re: Yanmar 1GM Overtemp Alarm / Thermostat

Check the overheat sensor. Remove and heat in water, check with ohmmeter, the contacts (between the terminal and the body) should close around 60C.
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Old 06-07-2019, 23:14   #9
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Re: Yanmar 1GM Overtemp Alarm / Thermostat

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Originally Posted by lockie View Post
....
If you're still unsure, reassemble the cooling system but leave the thermostat out, run up close to operating temperature, then close the bypass line (use a small vicegrips to squeeze the hose). This way you are guaranteed full flow through the engine, and now you can run it hard to see if the alarm still goes off. If you just remove the 'stat without constricting the bypass almost all the water will go through the bypass and the engine will quickly overheat.
...........
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Old 07-07-2019, 02:14   #10
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Re: Yanmar 1GM Overtemp Alarm / Thermostat

Greetings and welcome aboard the CF, Dave.

Basic Engine Gauge Theory and Testing ➥ http://www.cruisersforum.com/forums/...sting-645.html
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Old 07-07-2019, 02:58   #11
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Re: Yanmar 1GM Overtemp Alarm / Thermostat

Thanks everyone for your valuable input !!!

After I replaced the impeller, I ran engine in mooring for 15 minutes (timed) at idle. No alarm. Assumed "problem solved".

Then went out on river, alarm went off within few minutes at cruising revs (around 2000)

I don't know if above "means anything". Hot summer I would have thought the idling would have brought on alarm if a problem.

Hopefully down to boat today to try everyone's suggestions.
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Old 07-07-2019, 04:57   #12
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Re: Yanmar 1GM Overtemp Alarm / Thermostat

Quote:
Originally Posted by Delawaredave View Post
Thanks everyone for your valuable input !!!

After I replaced the impeller, I ran engine in mooring for 15 minutes (timed) at idle. No alarm. Assumed "problem solved".

Then went out on river, alarm went off within few minutes at cruising revs (around 2000)

I don't know if above "means anything". Hot summer I would have thought the idling would have brought on alarm if a problem.

Hopefully down to boat today to try everyone's suggestions.
Very little fuel is burnt at idle so very little heat is produced; much more fuel burnt at 2000 rpm under load so much more heat is produced.

For the other posters, please remember this engine is raw water cooled.
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Old 07-07-2019, 11:17   #13
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Re: Yanmar 1GM Overtemp Alarm / Thermostat

Hi All.
First post. I have had both a !gm and a 2gm. They both had the same overheating problem when I first obtained them in that the pipe above the pump had become clogged with a scale like substance. Easy fix. Strip and clear.
I expect you have checked these but sometimes it is worth stating the obvious.

Cheers. john
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Old 08-07-2019, 01:57   #14
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Re: Yanmar 1GM Overtemp Alarm / Thermostat

Greetings and welcome aboard the CF, John.
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Old 08-07-2019, 07:09   #15
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Re: Yanmar 1GM Overtemp Alarm / Thermostat

Water strainer plugged a bit? Inlet thru hull?
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