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Yanmar 2GM

Jun 24, 2021
11
S2 8.6 Norfolk
I have an overheating issue. I have dove and made sure throughhull is clean, strainer is clear, replaced impeller, new mixer elbow and fitting. It is spurting water out the exhaust. It’s raw water cooled, no heat exchanger.
My next job is to pull the thermostat and check it.

My question is will a thermostat cause it to overheat even if I’m having flow out the exhaust.

I’m also looking for a service manual for an 1985 yanmar 2GM
 

Blitz

.
Jul 10, 2007
609
Seidelmann 34 Atlantic Highlands, NJ
to answer your question, yes you engine expells water even if the thermostat doesn't open

if you haven't recently done so, changing the thermostat is a good place to start especially if you have flow, as well as checking the impeller, belt tension and strainer..

also, check flow from the thru Hull tracing the system

if impeller blades are missing you might have a bit of an adventure finding them. zincs also can break of and get stuck to reduce flows.
 
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Jun 24, 2021
11
S2 8.6 Norfolk
to answer your question, yes you engine expells water even if the thermostat doesn't open

if you haven't recently done so, changing the thermostat is a good place to start especially if you have flow, as well as checking the impeller, belt tension and strainer..

also, check flow from the thru Hull tracing the system

if impeller blades are missing you might have a bit of an adventure finding them. zincs also can break of and get stuck to reduce flows.
Everything is clear and I’ve replaced impeller, belt, all hoses. The thermostat is the only thing left in the system
 
Jan 30, 2012
1,088
Nor'Sea 27 "Kiwanda" Portland/ Anacortes
In this motor - the thermostat (motor cold) forces water to pass directly to the mixing elbow. When the temperature rises the thermostat opens. This does two things - allows water to flow through cylinder head /block before it goes to the mixing elbow and the hot thermostat also closes the direct-to-elbow passage. Either way - at any temperature - the water eventually flows overboard. By the way hot in a direct cooled motor is about 105F - pretty cool as motors go.

Make sure the thermostat housing (the cover) is not installed upside down. This mistake is real easy to do. There are other possibilities - one hopes the thermostat is the culprit.

Here is your manual - courtesy of this very website.

Yanmar_1GM-10L_2GM-F-L_3GM-D-F-L_3HM-F-L.pdf (sailboatowners.com)

Charles
 
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Jun 24, 2021
11
S2 8.6 Norfolk
In this motor - the thermostat (motor cold) forces water to pass directly to the mixing elbow. When the temperature rises the thermostat opens. This does two things - allows water to flow through cylinder head /block before it goes to the mixing elbow and the thermostat also closes the direct-to-elbow passage. Either way at any temperature the water flows overboard.

Here is your manual - courtesy of this very website.

Yanmar_1GM-10L_2GM-F-L_3GM-D-F-L_3HM-F-L.pdf (sailboatowners.com)

Charles
Thank you.
 
Nov 12, 2009
170
J/ 32 NCYC, Western Lake Erie
I'd be tempted to pull the thermostat out and run the engine without for a bit to see if it still overheats. And once the thermostat is out you can put it in a pot of cold water and bring the water to a boil to see if the thermostat opens.
 
Jan 30, 2012
1,088
Nor'Sea 27 "Kiwanda" Portland/ Anacortes
Sailor Sue - if you do that the water will pass to the mixing elbow both via the overflow and through the motor at the same time. This will probably not yield useful results unless you squeeze off the bypass hose with some visegrips thus forcing all the water through the block/head assembly.

Charles
 
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Oct 24, 2010
2,390
Hunter 30 Everett, WA
It's pretty easy to put that thermostat in a pan of water and test it. My biggest concern would be clogged cooling passageways. But you certainly need to rule out the simple things first.
 
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Blitz

.
Jul 10, 2007
609
Seidelmann 34 Atlantic Highlands, NJ
Sailor Sue - if you do that the water will pass to the mixing elbow both via the overflow and through the motor at the same time. This will probably not yield useful results unless you squeeze off the bypass hose with some visegrips thus forcing all the water through the block/head assembly.

Charles
visegrip....
 
Jun 24, 2021
11
S2 8.6 Norfolk
This is the cooling system.. I found a small fish in the thermostat cover on a friend's 2GM .. it overheated.
I’ve ordered a new thermostat and will pull that part of the system as soon as it comes in. The boat sat for 4 years it was an inheritance kinda thing. the motor runs fabulously less the cooling issue.
 

RoyS

.
Jun 3, 2012
1,162
Hunter 33 Steamboat Wharf, Hull, MA
Could be air bubble keeping thermostat out of coolant. Burp.
 
Jun 24, 2021
11
S2 8.6 Norfolk
Could be air bubble keeping thermostat out of coolant. Burp.
I burped it at all the hose connections. I didn’t have a gasket for thermostat housing is the only reason I hadn’t done it yet. I wasn’t aware of how the thermostat completely diverted water flow ( thanks to comments here) or it would have been part of my maintenance.

But thanks for your input. Every positive comment is a step forward
 
May 29, 2018
294
Canel 25 foot Shiogama, japan
Hi Vicegrip.
In the future be aware that you can simply make most of your own gaskets (except head gasket)
A cornflakes box, scissors and a hole punch and you are on the road again.

Gary


gray
 
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Blitz

.
Jul 10, 2007
609
Seidelmann 34 Atlantic Highlands, NJ
way to go, and to stay at it. think of all you learned about your engine that should help you in the future.
 
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