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Old 06-10-2019, 13:14   #1
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Does anyone replace thermostat...

...as part of periodic maintenance? It's not listed in the manual as something that needs to be done at any maintenance interval, but then again I've learned that the manual is far from comprehensive. I'm planning to change the coolant in my 4JH5E this year and wondering if it makes sense to swap out the thermostat for good measure. Thoughts? Thanks
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Old 06-10-2019, 13:29   #2
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Re: Does anyone replace thermostat...

It is listed as a maintenance item in our 1980 Yanmar ysm8. Check every 300 hrs & replace after 2000 hrs or 1 year????. Ours is 7 years old AFAIK but probably much older going by the P.O.'s maintenance or lack of should I say.
We tested ours in a pot of water on the stove with a thermostat which is a Yanmar recommended procedure. Ours is a raw-water cooled so its meant to start opening at 52oC but I suppose yrs is fresh water cooled so maybe about 80oC? but check in manual.
hope that helps
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Old 07-10-2019, 12:15   #3
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Re: Does anyone replace thermostat...

I occasionally test mine by throwing it in a pot of hot water on the stove – actually, I've recently removed it altogether because it promotes blockage of the exhaust manifold on my engine with anode oxidation residue – I do mainly short runs and the thermostat doesnt get warm enough to open and flush the manifold. There was no thermostat in place when I bought the boat, I didnt give it much thought, just bought one and stuck it in, but after quite a few years I realised it had been removed by the previous owner because of the above mentioned problem. Taking it out of the system is harmless in engineering terms and beneficial in that it forestalls a potentially damaging blockage.
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Old 07-10-2019, 12:29   #4
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Re: Does anyone replace thermostat...

Not letting your engine get up to operating temperature.. ever.. is not harmless.. If your engine gets up to operating temperature without a thermostat on short or low-load runs... you have blockage. Its not an unnecessary part - or the OEM wouldn't have bothered with the expense.


Quote:
Originally Posted by charliehows View Post
I occasionally test mine by throwing it in a pot of hot water on the stove Ė actually, I've recently removed it altogether because it promotes blockage of the exhaust manifold on my engine with anode oxidation residue Ė I do mainly short runs and the thermostat doesnt get warm enough to open and flush the manifold. There was no thermostat in place when I bought the boat, I didnt give it much thought, just bought one and stuck it in, but after quite a few years I realised it had been removed by the previous owner because of the above mentioned problem. Taking it out of the system is harmless in engineering terms and beneficial in that it forestalls a potentially damaging blockage.
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Old 07-10-2019, 12:43   #5
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Re: Does anyone replace thermostat...

yep, in theory. try telling that to a 40 year old engine still running like a sewing machine.
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Old 07-10-2019, 14:42   #6
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Re: Does anyone replace thermostat...

Quote:
Originally Posted by OrangeCrush View Post
...as part of periodic maintenance? It's not listed in the manual as something that needs to be done at any maintenance interval, but then again I've learned that the manual is far from comprehensive. I'm planning to change the coolant in my 4JH5E this year and wondering if it makes sense to swap out the thermostat for good measure. Thoughts? Thanks
Thermostats do have a long life in coolant cooled engines and if you have a water temperature gauge fitted, you usually get advance warning of potential thermostat issues. In fact, if I had to choose between replacing a working thermostat or fitting a water temperature gauge, I would choose the gauge.

However replacing the thermostat should not break the bank (even a Yanmar one ).

Be aware the thermostat on raw water cooled engines have different functions to that of a thermostat on a coolant cooled engines so service manual recommendations can't be transferred from type of engine to another.

Another issue with raw water cooled engines is that almost all water temperature gauges are next to useless so one doesn't get advanced warning of thermostat issues. The gauge will not tell you if the engine is running too cold or slightly overheating.
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Old 07-10-2019, 15:18   #7
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Re: Does anyone replace thermostat...

[QUOTE=Wotname;2992196]Thermostats do have a long life in coolant cooled engines and if you have a water temperature gauge fitted, you usually get advance warning of potential thermostat issues.



What is the warning?
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Old 07-10-2019, 15:31   #8
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Re: Does anyone replace thermostat...

Not as part of periodic maintenance but when changing coolant, yeah, why not ? Any hoses that look skanky or are of an advanced age, check the preformed ones on the engine too. Because you won't have to change it often.
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Old 07-10-2019, 16:12   #9
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Re: Does anyone replace thermostat...

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Originally Posted by Calif.Ted View Post
Not as part of periodic maintenance but when changing coolant, yeah, why not ? Any hoses that look skanky or are of an advanced age, check the preformed ones on the engine too. Because you won't have to change it often.
I agree. The nice thing about changing a thermostat that works perfectly is that you save it as a spare and you are certain that if you use it to replace a thermostat which has failed in the future it will work till you can replace it with a new one.
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Old 07-10-2019, 17:01   #10
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Re: Does anyone replace thermostat...

Thanks for the replies. Yeah the engine is only about 6 years old with 800 hours on it, but it couldn't hurt to change it out. Now, any tips on finding the right part number for a Yanmar 4JH5X1? Or how to go about changing it? I'm digging around the internet but like I said the manual leaves a lot to be desired. Thanks very much.
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Old 07-10-2019, 17:07   #11
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Re: Does anyone replace thermostat...

Quote:
Originally Posted by Ecos View Post
.......



What is the warning?
I didn't include the warning mechanism 'cause I thought it was obvious - my bad!

Engine temperature begins to operate outside it's normal range - either too or too cold; of course you gotta look at the gauge and be aware of all the other circumstances that might cause such fluctuations.

However I understand you are a pilot so I'm sure you are well versed in understanding the need to monitor temperatures from a variety of inputs.


And again allow me to repeat, this option isn't really applicable to raw water cooled engines. Because their normal operational temperature is well below the mid range of most temperature gauges.
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Old 07-10-2019, 17:12   #12
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Re: Does anyone replace thermostat...

Quote:
Originally Posted by OrangeCrush View Post
Thanks for the replies. Yeah the engine is only about 6 years old with 800 hours on it, but it couldn't hurt to change it out. Now, any tips on finding the right part number for a Yanmar 4JH5X1? Or how to go about changing it? I'm digging around the internet but like I said the manual leaves a lot to be desired. Thanks very much.
Ask your local Yanmar agent and get a thermostat housing gasket at the same time unless you plan on making your own gasket.
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Old 07-10-2019, 17:17   #13
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Re: Does anyone replace thermostat...

Every 4 to 5 years, when you also need to replace your coolant hoses. If you go longer,you will spend hours trying to remove the rusted t-stat or crusty hose clamps. Many boat items need to replaced before their life cycle is up just because of the environment they run in. Learned that by watching a marine mechanic use an acetylene torch to break apart an outboard lower unit that the owner let go for 10 years without replacing the water pump impeller.
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Old 07-10-2019, 17:26   #14
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Does anyone replace thermostat...

Quote:
Originally Posted by OrangeCrush View Post
...as part of periodic maintenance? It's not listed in the manual as something that needs to be done at any maintenance interval, but then again I've learned that the manual is far from comprehensive. I'm planning to change the coolant in my 4JH5E this year and wondering if it makes sense to swap out the thermostat for good measure. Thoughts? Thanks


I would replace it, because for one thing you likely donít know how old it is.
But then Iím replacing all my coolant hoses this year when I clean the heat ex. I did the thermostat last time I did coolant, which I do every two years. All my hoses are fine, and they are 32 yrs old, a few that I have replaced so far were as hard as rocks, very likely that removal would have caused one or crack, and then of course itís not serviceable. However they all seem to be 25mm or 1Ē, so a few ft of 1Ē hose would have worked to get me home, routing may not have been pretty but you could get home.
I dislike carrying spare hoses as they age sitting in spares, and the three little fresh water hoses for my 4JHE were about $90
Take the old one and do not throw it away, put it in spares.
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Old 07-10-2019, 17:30   #15
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Re: Does anyone replace thermostat...

Quote:
Originally Posted by charliehows View Post
I occasionally test mine by throwing it in a pot of hot water on the stove – actually, I've recently removed it altogether because it promotes blockage of the exhaust manifold on my engine with anode oxidation residue – I do mainly short runs and the thermostat doesnt get warm enough to open and flush the manifold. There was no thermostat in place when I bought the boat, I didnt give it much thought, just bought one and stuck it in, but after quite a few years I realised it had been removed by the previous owner because of the above mentioned problem. Taking it out of the system is harmless in engineering terms and beneficial in that it forestalls a potentially damaging blockage.

This is interesting (to me at least ).
You have Yanmar QM series raw water cooled (RWC) engine and the thermostat in RWC QM series regulates the temperature of the water passing though the exhaust manifold rather than directly on the temperature of the water in the head. As best as I understand it, with this arrangement the head temperature should in theory be a little cooler than the exhaust manifold . I don't know if this is a good thing or a bad thing but Yanmar designed it this way!

CH, did you remove or otherwise block the bypass water to the manifold when you removed the thermostat?

Will water still drain out of the lower drain tap on your manifold?

I have one where the manifold was 3/4 clogged - there was no way water was passing though the middle or bottom sections of the manifold and the crud could only be removed by cutting open the lower section of the cast iron manifold.
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