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post #1 of 12 Old 10-28-2019 Thread Starter
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Confirming an open thermostat

How do you know when the thermostat opens up?

Canadian winterizing includes running antifreeze through the cooling system.

The protocol for my raw-water cooled Yanmar 2GM20:

1. Haul out.
2. Disconnect raw water hose from thru-hull, put it in a bucket of water.
3. Idle the engine until operating temperature.
4. Move raw water hose to a bucket of antifreeze.
5. Wait for antifreeze to exit the exhaust.
6. Wait impatiently for spring.

For step 3, I just feel the exhaust water by hand until the temperature stabilizes. That's about 20 minutes at idle.

My assumption is that the stable temperature means that the thermostat has opened, which lets antifreeze reach every part of the cooling system.

Is my assumption correct?

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Last edited by Degas; 10-28-2019 at 01:35 PM.
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post #2 of 12 Old 10-28-2019
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Re: Confirming an open thermostat

You should see the temp gauge move off the stop then move to operating temp
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Re: Confirming an open thermostat

Quote:
Originally Posted by RegisteredUser View Post
You should see the temp gauge move off the stop then move to operating temp
Sorry, I forgot to mention that I don't have a temp gauge.

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Re: Confirming an open thermostat

I would just remove the Thermostat if you're not sure of proper coverage, tie it off right there so you don't forget to put it back in, but they all bypass some anyway. I'm sure on the hard you won't run long enough to warm and open it anyway. I stay in the water and take precautions if it gets really cold as most do (that stay in the water anyway).
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On my raw water cooled boats I just take the stat out and reinstall the cover. It's only two screws and readily accessible. Without a load the engine won't get hot wet to fully open it anyway. On a fresh water engine it's not necessary, that circuit is (or should be) full of antifreeze. You can check it's potency with a coolant hydrometer. The raw water circuit doesn't rely on the stat so you can just run it out of a bottle of AF until it comes out the exhaust.
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Re: Confirming an open thermostat

Yup. Pull the thermostat out. Should be fairly easy. Helps insure nothing got past the sea strainer and held up there too. Given it's constant exposure to raw water, testing it in hot water over the winter, to insure it's functioning properly, isn't a bad idea either. Something to do on a cold snowed in day.


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Testing the stat is actually kind of fun. Put it in a pot of water on the stove with a cooking thermometer and you can watch it open at the proper temperature. If it doesn't, replace it.
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post #8 of 12 Old 10-29-2019
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Re: Confirming an open thermostat

Is this a raw water-cooled engine or do you have a heat exchanger? With a heat exchanger, the thermostat is on the coolant (freshwater) side, so you shouldn't have to remove the thermostat. If it is raw-water cooled, then I guess it would make sense to remove the thermostat. In either case, I'd run plenty of nontoxic antifreeze through it to make sure all the water is flushed out before you shut it down. In other words, don't just shut it down as soon as you see antifreeze coming out of the exhaust. Buy some extra nontoxic antifreeze and let the engine run a bit longer. You can always disconnect your exhaust hose and collect the antifreeze in buckets, which you can then use to winterize your head and holding tank.
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Re: Confirming an open thermostat

Quote:
Originally Posted by Degas View Post
....The protocol for my raw-water cooled Yanmar 2GM20:
Quote:
Originally Posted by Damon Gannon View Post
Is this a raw water-cooled engine or do you have a heat exchanger?.....
The OP said raw water, hence the advice to remove the thermostat.


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Re: Confirming an open thermostat

Thanks for the tips so far.

Indeed, removing the thermostat is guaranteed to get coolant flowing everywhere in a raw-water engine.

Follow-up: Instead of removing the thermostat, how would I use a handheld infrared thermometer to test that the thermostat is open or closed?

I would be looking for a change in temperature at some part of the engine, right? Where would I aim the thermometer on a raw-water cooled engine?

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Last edited by Degas; 10-29-2019 at 01:20 PM.
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