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Old 05-03-2013, 22:34   #1
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2GM20F Heat Switch question ...

The heat switch on my Yanmar 2GM20F threads into the thermostat housing and I understand it works by using thermal expansion material that makes the contact when it gets too hot setting off the over-heat alarm.

My old one broke (expansion material chipped off along with the wire connector), and in replacing it I could not figure out how far to thread it in. I stopped with a reasonable amount of tightness.

Fired it up and didn't run for five minutes before the alarm went off. (Engine wasn't hot), so disconnected the wire and went sailing for the weekend with no problems.

Question: Do I back the switch off, (unscrew it) until it stops sending the alarm? How do you know when to stop tightening?

The color of the expansion material was yellow instead of green in this switch, could it be a different temp setting?

Could it be that my thermostat isn't opening at a low enough temp setting off the alarm after just a few minutes?

I thought I had this fixed! Arrrr
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Old 05-03-2013, 23:05   #2
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Re: 2GM20F Heat Switch question ...

Quote:
Originally Posted by eliems View Post
The heat switch on my Yanmar 2GM20F threads into the thermostat housing and I understand it works by using thermal expansion material that makes the contact when it gets too hot setting off the over-heat alarm.

My old one broke (expansion material chipped off along with the wire connector), and in replacing it I could not figure out how far to thread it in. I stopped with a reasonable amount of tightness.

Fired it up and didn't run for five minutes before the alarm went off. (Engine wasn't hot), so disconnected the wire and went sailing for the weekend with no problems.

Question: Do I back the switch off, (unscrew it) until it stops sending the alarm? How do you know when to stop tightening?

The color of the expansion material was yellow instead of green in this switch, could it be a different temp setting?

Could it be that my thermostat isn't opening at a low enough temp setting off the alarm after just a few minutes?

I thought I had this fixed! Arrrr
The temperature switch threads are tapered pipe thread. You put some thread lube/sealant on the threads, tefon tape is one type and tighten to prevent leaks. The threading has nothing to do with temperature.

There are two types of cooling, raw water and closed loop. Raw water cooling puts salt water through all the engine passages. To minimize corrosion and salts precipitating out in the passages and clogging them raw water engines are operated at a lower temperature.

My GM manual states that raw water engine thermostats fully open at 52 degrees C and the temperature switch for those engines are colored yellow. The closed loop, (fresh water cooled engine), designated by the F on your model number have a thermostat that fully opens at 85 degrees C and have a temperature switch colored brown.

I did not find at what temperature the raw water switch alarms at, but the fresh water switch alarms at 10 degrees over normal temp, so having the wrong switch in your engine alarming at normal fresh engine temps seems reasonable.

John
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Old 06-03-2013, 06:55   #3
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Re: 2GM20F Heat Switch question ...

Remove the switch and hook up an ohm meter. Put it in a pan of water on a stove with a thermometer in the water. Heat the water until the switch closes. Should close at about 200 F.

David
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Old 11-03-2013, 10:50   #4
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Re: 2GM20F Heat Switch question ...

Exactly right. Thank you for this answer! Got the correct switch, (actually green in color), and it is working perfectly. They had given me the raw water switch which as you say, opens at a lower temp.


Quote:
Originally Posted by cal40john View Post
The temperature switch threads are tapered pipe thread. You put some thread lube/sealant on the threads, tefon tape is one type and tighten to prevent leaks. The threading has nothing to do with temperature.

There are two types of cooling, raw water and closed loop. Raw water cooling puts salt water through all the engine passages. To minimize corrosion and salts precipitating out in the passages and clogging them raw water engines are operated at a lower temperature.

My GM manual states that raw water engine thermostats fully open at 52 degrees C and the temperature switch for those engines are colored yellow. The closed loop, (fresh water cooled engine), designated by the F on your model number have a thermostat that fully opens at 85 degrees C and have a temperature switch colored brown.

I did not find at what temperature the raw water switch alarms at, but the fresh water switch alarms at 10 degrees over normal temp, so having the wrong switch in your engine alarming at normal fresh engine temps seems reasonable.

John
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