Yanmar thermostat not closing

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richardabeattie

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I have just put the thermostat from my (10 year old) raw water cooled 2GM20 into a cup of freshly boiled water and it has not closed. Does that mean the water is not hot enough or that the thermostat has had it? What can have gone wrong with such a simple bit of kit?
 
richardabeattie said:
I have just put the thermostat from my (10 year old) raw water cooled 2GM20 into a cup of freshly boiled water and it has not closed. Does that mean the water is not hot enough or that the thermostat has had it? What can have gone wrong with such a simple bit of kit?
Click to expand...

I have had two Yanmar thermostats fail in 7 years.
They are about £85 each.
The other thing is they fail in such a way the engine overheats instead of the engine never getting hot.
 
richardabeattie said:
I have just put the thermostat from my (10 year old) raw water cooled 2GM20 into a cup of freshly boiled water and it has not closed. Does that mean the water is not hot enough or that the thermostat has had it? What can have gone wrong with such a simple bit of kit?
Click to expand...

Maybe I misunderstand but they open when hot and close when cold.

They are usually marked with the opening temp and that is the temp at which they just start to crack open... often difficult to see. Sometimes also marked with the temperature at which they are fully open.


They dont always last forever... just replaced one in one of our cars that was opening 10° too low. Had one fall apart once too.

Not personally ever had one fail closed and cause overheating although that would be the more obvious thing to happen.
 
Thanks for your replies. Deeply moved by the ludicrous cost of this very simple bit of kit and with nothing to loose I took a little hammer to the inner end and tapped it a few times and then tapped the outer end and, Lo and Behold, it unstuck itself.

Whatever should I do without the forum and how should I spend the £85?
 
richardabeattie said:
I have just put the thermostat from my (10 year old) raw water cooled 2GM20 into a cup of freshly boiled water and it has not closed. Does that mean the water is not hot enough or that the thermostat has had it? What can have gone wrong with such a simple bit of kit?
Click to expand...

The thermostat has failed. At ambient temperature, it should be closed. For your engine, the thermostat should start to open at 42degC and be fully open at 52degC. You'll have to replace it - the correct new one should have the opening temperature (42) stamped on it.
 
richardabeattie said:
Thanks for your replies. Deeply moved by the ludicrous cost of this very simple bit of kit and with nothing to loose I took a little hammer to the inner end and tapped it a few times and then tapped the outer end and, Lo and Behold, it unstuck itself.

Whatever should I do without the forum and how should I spend the £85?
Click to expand...

I'm not sure I'd be happy to rely on it working properly.
 
VicS said:
Not personally ever had one fail closed and cause overheating although that would be the more obvious thing to happen.
Click to expand...

The thermostat on my wifes VW Polo also failed. I was very surprised to get the call the car had overheated. I took water with me and filled the radiator back up, Then drove home abandoning the car several times to allow it to cool back down.
I looked at everything else before I checked the thermostat because I couldn't believe it would fail in the position that allowed the car to overheat. The VW Polo thermostat housing is plastic and looking at it I was surpised it lasted any time at all.
 
richardabeattie said:
I have just put the thermostat from my (10 year old) raw water cooled 2GM20 into a cup of freshly boiled water and it has not closed. Does that mean the water is not hot enough or that the thermostat has had it? What can have gone wrong with such a simple bit of kit?
Click to expand...

Thermostat has their rating stamped onit. Place into a kettle with enough water to cover it. Boil the kettle when the kettle is boiling it should then open between the rating stampted on the thermostat there are different types but if it does not open then the thermostat is faulty.

Make sure when you take the thermostat out if its open place it under a running tap cold water is should then close if it dosn't thermostat is faulty.

Alain
 
Thanks again. It is now opening in hot water and closing when cold. The stamping on the inner end says 2 C I F (I think!) so I'm none the wiser but I shall reinstall it and check it more frequently.
 
I was thinking of buying a spare. but I hadn't realised that a Yanmar thermostat was as expensive. Don't know why I'm surprised though given the usual price of marine diesel spares.

I found one for my engine at £81.66 + Del. (Though a hand written £35.91 is clearly visible in the picture :))
http://www.marine-power.co.uk/index.php?route=product/product&path=20_78_119&product_id=262

US seems cheaper though (surprise) $62.66 (~(£39)
http://acemarinediesel.com/marine-e...-engine-parts/yanmar-129470-49801-thermostat/

Even cheaper at $24.87 here (~£15.46)
http://www.rpmdiesel.com/store/parts.cfm?manu=Northern Lights&search=THERMOSTAT
 
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I paid around £40 including post for a yanmar thermostat for a 2qm15 which compared to some was less than half their price
If I were the poster there's no way I'd rely on an iffy thermostat chuck it fit a new one !

mick
 
It was gunged up. I tapped it to free it up, cleaned it out and it now opens and closes as advertised. If in the future it fails open then the engine will take longer to heat up and if it fails closed the engine will overheat and sound its alarm. So why change it?
 
Hi Richard. Its often the case that this very simple device can stick closed due to corrosion and limescale, especially if your system was filled with hard water. If it has a cake of white deposit use a propriatory household cleaner like limelite on it rather than whacking it with a Glaswegian screwdriver.... Also if you want a replacement take it to your local motor factor and ask for an equivalent. It's not a marine engine specific part I don't think so don't pay Yanmar prices.
 
Unfortunately I think that boat thermostats are specific to marine engines because they operate at a different temperature range than automotive parts. Worth try though.
 
There are a variety of temperature ranges available for both marine and automotive uses. I have not yet found it impossible to find an equivalent.
 
boatmike said:
There are a variety of temperature ranges available for both marine and automotive uses. I have not yet found it impossible to find an equivalent.
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The Yanmar thermostat opens at 42degC, which as ghostlymoron suggested is a bit cool for automotive applications. Anyway, the genuine Yanmar one is only about £30 (not £85 as alleged earlier in this thread).
 
ghostlymoron said:
As a temporary 'get you home' measure with car or boat, you can take the element out. The engine will run cool but not suffer damage.
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That isn't true of some raw-water cooled engines, including both Yanmar and Bukh. As the thermostat opens the upper part of it closes off the bypass, forcing water to pass through the engine block. If the thermostat is removed the water takes the path of least resistance, i.e. through the bypass, and the engine is likely to overheat. Volvo thermostats are a mystery to me: I have no idea how they control engine temperature, so the same may apply to them, or not.
 
vyv_cox said:
That isn't true of some raw-water cooled engines, including both Yanmar and Bukh. As the thermostat opens the upper part of it closes off the bypass, forcing water to pass through the engine block. If the thermostat is removed the water takes the path of least resistance, i.e. through the bypass, and the engine is likely to overheat. Volvo thermostats are a mystery to me: I have no idea how they control engine temperature, so the same may apply to them, or not.
Click to expand...

I don't understand the Volvo thermostat system, either, and I've got one! It is especially puzzling that the take-off for the calorifier (pictured on Vyv's website) appears to be in the bypass loop! I can vouch for the fact that the calorifier works, so I am sure that both Vyv and I would be glad of enlightenment - ideally, with diagrams for the hard of thinking :o
 
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