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Old 04-04-2019, 01:03 AM   #1
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Cooling System Cleaning

I have an older Yanmar 3HM. It is keel cooled and seems to be in good shape. The 3HM was designed for raw water cooling but was adapted to keel cooling by the builder. The engine temp runs at around 135-140F. I have looked into changing the thermostats to a higher temp but that option is not available. There is a way to do it with an external thermostat and I bought the thermostat and misc plumbing but decided not to bother with it.

The boat was on the hard all winter and one of the maintenance jobs I did was flushing and cleaning the cooling system with a radiator flush chemical. Before the boat ran at 140F or so. Now after cleaning the cooling system it is about 122F. The spec for the thermostats is opening at 108F and fully open at 126F so I guess it is working as it is supposed to. Disappointing though as I thought 140 was kind of low.

The reason I thought cleaning the cooling system might be good was that when I ran the engine wide open the temp would climb fairly high. I haven't tried max rpm since cleaning but I will.
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Old 04-04-2019, 01:26 AM   #2
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Diesels generally run more efficiently at higher temps. Usually 180° or above. I have seen economy increase by 2-6% running engines warmer. Since yours is no longer raw water cooled you could run it higher. I doubt Yanmar makes the thermostat. You can probably find a 180° thermostat that fits the engine.
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Old 04-04-2019, 05:04 AM   #3
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Why would you want to change what Yanmar says is correct? Yours seems to be running just as it should. Am I missing something?
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Old 04-04-2019, 05:33 AM   #4
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Raw water cooled engines have low temperature thermostats because high- 160+ temps will precipitate out salts and slowly foul the engine. Once the OP changed to keel cooling with antifreeze this problem went away and he could run up to 180 safely if he wanted to.


But as noted above running cool is just a little inefficient, no harm done. Since the temps did climb at high loads that was a good thing to do.


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Old 04-04-2019, 06:50 AM   #5
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Thermostats in a housing with 2 hose fittings might solve the problem ,
as would installing a by pass thermostat in the keel cooling discharge and return.

This would keep the water returning to the engine at a selected temperature .
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Old 04-04-2019, 07:48 AM   #6
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Originally Posted by djmarchand View Post
Raw water cooled engines have low temperature thermostats because high- 160+ temps will precipitate out salts and slowly foul the engine. Once the OP changed to keel cooling with antifreeze this problem went away and he could run up to 180 safely if he wanted to.


But as noted above running cool is just a little inefficient, no harm done. Since the temps did climb at high loads that was a good thing to do.


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Old 04-04-2019, 11:15 AM   #7
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Here is the thermostat for my engine. My engine has two side by side. It is very small, less than 1" diameter. I have talked to parts suppliers and searched online and haven't come up with anything.
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Old 04-05-2019, 05:24 AM   #8
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So this engine, when raw water cooled, circulates raw water directly through the engine? I.e. no heat exchanger? As David said, that would explain the low operating temp.


Those are indeed funky thermostats. If you want to run at a higher and more regulated temp, it seems that installing the external thermostatic bypass is the way to go.
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Old 04-05-2019, 09:26 AM   #9
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So this engine, when raw water cooled, circulates raw water directly through the engine? I.e. no heat exchanger? As David said, that would explain the low operating temp.


Those are indeed funky thermostats. If you want to run at a higher and more regulated temp, it seems that installing the external thermostatic bypass is the way to go.
The engine is keel cooled. No raw water in engine now through it was originally designed as raw water cooled.
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Old 04-05-2019, 10:41 AM   #10
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Whoops....

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Originally Posted by djmarchand View Post
Raw water cooled engines have low temperature thermostats because high- 160+ temps will precipitate out salts and slowly foul the engine. Once the OP changed to keel cooling with antifreeze this problem went away and he could run up to 180 safely if he wanted to.

David

No, that's backward, and wrong on multiple levels. Saltwater solutions at the saturation point will precipitate salt out of solution when the solution is cooled, not heated.


https://socratic.org/chemistry/solut...ated-solutions


In general, this is true of all solutions. If mom ever taught you how to make rock-candy strings, you'll remember how this works.


Moreover, typical seawater is about 3.5% salt by weight. The saturation point for NaCl in H2O is 26% by weight. Salt can only precipitate out when the solution is saturated. There is no body of water on earth where the salinity comes anywhere close to saturation, so in effect, "precipitation" of salt out of seawater is literally impossible.



The real reason that raw-water cooled systems may use a lower thermostat temp is to increase the safety margin between the thermostat temp and the boiling point of the coolant. Antifreeze boils somewhere above 260 (depending on concentration) and seawater boils at just a tiny fraction of a degree above 212. Inside an engine, "pocket" areas of intense heat (tops of cylinder walls) can raise the coolant temp well above the temp at which the thermostat opens. In these areas, the coolant could transition to vapor and deprive these areas of full cooling, so we need to keep raw-water coolant well below that.



If you want to see this with your own eyes, put a pot of water onto an electric stove burner and watch as the bubbles form just above the coils of the heating element. You'll see this long before the entire pot comes to a boil.


Compounding the problem for seawater cooled systems (vs. freshwater) is the fact that the thermal conductivity of water decreases with increasing salinity.
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Old 04-05-2019, 11:34 AM   #11
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Originally Posted by ak-guy View Post
The engine is keel cooled. No raw water in engine now through it was originally designed as raw water cooled.

Sorry, I meant as the engine was originally designed.


If the original design was to have raw water circulating through the engoine's water jackets, then I could see the lower "coolant" operating point.


If on the other hand it was designed as a heat exchanger setup with gylcol coolant circulating through the engine jackets, and raw water only through a heat exchanger, then I would expect the coolant operating temp to be in the more "normal" 160-190 range.
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Old 04-05-2019, 11:37 AM   #12
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Be careful, call Yanmar!

Quote:
Originally Posted by ak-guy View Post
I have an older Yanmar 3HM. It is keel cooled and seems to be in good shape. The 3HM was designed for raw water cooling but was adapted to keel cooling by the builder. The engine temp runs at around 135-140F. I have looked into changing the thermostats to a higher temp but that option is not available. There is a way to do it with an external thermostat and I bought the thermostat and misc plumbing but decided not to bother with it.



The boat was on the hard all winter and one of the maintenance jobs I did was flushing and cleaning the cooling system with a radiator flush chemical. Before the boat ran at 140F or so. Now after cleaning the cooling system it is about 122F. The spec for the thermostats is opening at 108F and fully open at 126F so I guess it is working as it is supposed to. Disappointing though as I thought 140 was kind of low.

The reason I thought cleaning the cooling system might be good was that when I ran the engine wide open the temp would climb fairly high. I haven't tried max rpm since cleaning but I will.
I had a brief look at the Yanmar factory manual online just now.

Your engine was (as you say) designed to be cooled by raw water. It uses a rubber impeller designed to draw in water in the range of 32-degrees to about 90-degrees or so. If you are going to now be putting hotter water into your keel-cooler, what will be the temperature of the water now hitting your rubber impeller?

re: "when I ran the engine wide open the temp would climb fairly high."

And there is your evidence that the cooling system needed cleaning. In the circumstance you describe, that T-stat would have been wide open at 126 degrees, and so the incoming water temp must have been quite high. I would be concerned about running hot water into that rubber impeller at much higher temps than it was designed for -- likely will have softened or other wise damaged it the impeller. When you shut down the engine, a heated rubber impeller will take a 'set'. Over time it will harden and crack prematurely. I would replace the impeller and keep it as cool as possible going forward.

Re: "The 3HM was...adapted to keel cooling by the builder."

All the more reason to contact Yanmar. In my experience, the majority of 'builder modifications' to engines or their systems are done by people who are unqualified to do these mods, and/or have not discussed them with the engine manufacturer.

There are lots of reasons that Yanmar engineers may have chosen a 126 degree thermostat for that engine. Why mess with it? Of all the things I like to 'play around' with and 'tweak' on a boat or an engine, changing the factory-specified cooling system temperature "because I think it should be higher" is not one of them.

If it ain't broke, don't break it.

Lastly, why did the system need cleaning? A sealed system using good antifreeze that was so fouled that it could not keep your 27hp engine cool -- even with the T-stat wide open? You might have a gremlin in there. What did the coolant look like when it came out? Was there actually coolant in there, or just water?

Good luck!
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Old 04-05-2019, 11:48 AM   #13
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Similar Yanmar 3HM story?

Modifications to the cooling system causing big trouble...



Yanmar 3HM Overheating - Cruisers & Sailing Forums
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Old 04-05-2019, 11:55 AM   #14
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Please read this article by Ed Sherman published in Cruising World in 2001:


https://www.cruisingworld.com/how/ca...stem-take-heat


The pertinent paragraph is excerpted below:


"A more insidious drawback to the raw-water system is that the engine must run cooler than it could with a closed system. Above 160 F, sea salt begins to crystallize inside the cooling-system passages. This not only accelerates corrosion but also, in extreme cases, can actually block passages. For this reason, most raw-water-cooled diesels have a thermostat set at 145 F, at least 40 F cooler than a closed system. Running at this relatively lower temperature reduces an engine’s thermal efficiency, so a raw-water system simply is unable to produce as much usable power as its closed system counterparts."


I can't really explain the chemistry involved. Maybe mild cavitation in the cooling passages at high loads let Ca/Mg ions precipitate out or some similar phenomenon.


But setting the thermostats for raw water cooled engines to 14 5degrees or so has been a long standing practice. I can't think of any other reason to do this.



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Old 04-05-2019, 01:13 PM   #15
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Please read this article by Ed Sherman published in Cruising World in 2001:...

I can't really explain the chemistry involved. Maybe mild cavitation in the cooling passages at high loads let Ca/Mg ions precipitate out or some similar phenomenon.

But setting the thermostats for raw water cooled engines to 14 5degrees or so has been a long standing practice. I can't think of any other reason to do this.

David
First off, "crystalize" and "precipitate" are two utterly different and unrelated things. When salt water evaporates (at any temperature) you will have salt crystals left behind. When water is applied, the crystals will dissolve and wash away, once again, regardless of temperature.

No matter. Neither precipitation, nor crystalization, nor any other scale buildup of anything whatsoever is the problem here.


This myth has been around a long time. I suspect Ed Sherman heard it from someone who heard it from someone who heard it from someone. It sounded good, so no one ever thought to question it. Ed Sherman is a really smart guy, but he's not an engineer.

https://www.bandofboaters.com/forum/...perature/page2

re: "I can't really explain the chemistry involved. Maybe mild cavitation in the cooling passages at high loads let Ca/Mg ions precipitate out or some similar phenomenon."

Nope...nothing remotely like that.

re: "But setting the thermostats for raw water cooled engines to 14 5 degrees or so has been a long standing practice. I can't think of any other reason to do this."

True, and I've already given the reason...but maybe you missed it (or just don't believe it ;-)

Back in my college days, my engineering physics teacher used this as a question on an exam.

Have a look at this, specifically: "coolant will boil in the cylinder head and next to the cylinder walls, forming vapor bubbles, and these areas will quickly overheat."

https://www.motor.com/magazine-summa...tem-diagnosis/

Now, because there is no coolant touching those locally overheated areas (only water vapor), this engine will quickly destroy itself.

The reason that raw water cooled engines need to run cooler is to prevent localized boiling and subsequent loss of cooling at the hottest and most critical places in the engine.

This has absolutely nothing to do with salt, or calcium or scale or anything else. It is true whether the raw-water is freshwater or seawater. It is even truer when the cooling system is not pressurized (whether there is antifreeze in there or not).

In my previous response I suggested visualizing this localized boiling phenomenon by looking in the bottom of a pot on an electric burner. Now remember that it's only gravity that are causing those bubbles to leave the area.

Turn the "pot" upside down. Make it a closed vessel, with a small vent somewhere. Apply the heat source to the TOP of the vessel. All of those water vapor bubbles are going to join up and make a pocket of water vapor. Our heat source is now insulated from the water by the water vapor pocket. Our heat source is no longer heating up the water, it is now heating up the metal, and the metal in that area will overheat until it melts.

This is why raw water cooled engines use lower temperature thermostats, no other reason.
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Old 04-05-2019, 01:27 PM   #16
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Here is the thermostat for my engine. My engine has two side by side. It is very small, less than 1" diameter. I have talked to parts suppliers and searched online and haven't come up with anything.

Yes, this is a very different t-stat from what most here are used to seeing. Don't mess with it.


Here's why:
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Old 04-05-2019, 01:38 PM   #17
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Picture of your setup...

Is this what you have?
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Old 04-05-2019, 01:47 PM   #18
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Part number and prices

Quote:
Originally Posted by ak-guy View Post
Here is the thermostat for my engine. My engine has two side by side. It is very small, less than 1" diameter. I have talked to parts suppliers and searched online and haven't come up with anything.

Here you go...


https://www.google.com/search?q=105582-49200
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Old 04-05-2019, 01:51 PM   #19
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From my library...the factory service manual:
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File Type: pdf yanmar-cooling-system-chapter8.pdf (3.83 MB, 13 views)
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Old 04-05-2019, 03:05 PM   #20
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Quote:
Originally Posted by Riverguy View Post
Is this what you have?
Yes that is my engine. The only difference is no water exhaust injection and the water pump is pumping coolant. Also I have the same factory service manual. Thanks
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