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Old 25-08-2020, 19:40   #1
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Yanmar 3GM30 over heat

Hi everyone,

Hope everyone is doing well and staying safe. New boat owner here of a C&c 35 Itís yanmar 3GM30 that been modified to be coolant cooled as well. in San Francisco

Anyways, I never touched an engine before with absolutely no experience. Got the boat and started to follow this awesome forum and did all the basic Maintinance from oil change, filters, impellers etc. However, my engine now heats up and the idiot temp alarm comes off.

My engine had unknown green coolant, I went ahead and flushed it and replaced it with the pink good stuff. While troubleshooting the overheat, I checked the impellers again(both new), pumps rotate with no problem or leak and sea water of the exhaust and no leakage anywhere. So I think it has to be the coolant circuit. Something weird is that the hose from the heat exchanger to the pump until the thermostat, stays cold. But from the thermostat to the engine block and the last hose from block to the heat exchanger is really hot. All hoses are replaced and checked for blockage. Is that an air block? If so, how can I bleed the system? Couldnít find that anywhere. Also after the engine cools, I opened all the hoses to check of the have flow on them, and they all had coolant except these last 2 from the engine block to the heat exchanger. Is that normal? Should I fill them up manually with coolant to try to get rid of any air blockage?

Last but not least, I may have trouble shoot the engine so much, and now I see steam that comes off or close by the 1st cylinder. Also a lot of blue smoke from the exhaust. That never happened before. Did I screw up?

Thank you again for your time
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Old 25-08-2020, 20:03   #2
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Re: Yanmar 3GM30 over heat

Ooh. Certainly hope you haven't screwed up anything. Blue smoke doesn't sound good. Have you looked to see what the level of coolant is inside the freshwater tank and also in the overflow (sub tank)? It is possible there was a big air bubble in the system. Anytime I do a coolant change, I check the levels several times to be sure fluid it's still full. Also, do you have coolant running to a water heater? Might check those lines too to make sure you don't have a leak somewhere.
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Old 25-08-2020, 20:07   #3
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Re: Yanmar 3GM30 over heat

Ya the blue smoke worries me too. And I donít have a water heater. Still have sea water comes in to the heat exchanger and out to the exhaust. I check the overflow for the coolant all the time and filled it half way. Thatís why Iím not sure why these 2 last hoses of the engine block are without coolant
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Old 26-08-2020, 05:21   #4
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Re: Yanmar 3GM30 over heat

So much like you, I am not an engine guy... learning as I go with my 3 gm30 f too. My concern is based off of what a mechanic once warned me of with my 1 tonne truck. Some coolants aren't compatible with others, and can gel up . If that happened, my guess would be in the heat exchanger.
Again i am NOT a mechanic, so this is really just a WAG.
Good luck and let us all know your findings so we can learn from you too
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Old 26-08-2020, 08:13   #5
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Re: Yanmar 3GM30 over heat

"My engine had unknown green coolant, I went ahead and flushed it and replaced it with the pink good stuff." Please tell us that you did not use pink water-system antifreeze as engine coolant! I hope you used the proper coolant as called for by Yanmar.
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Old 26-08-2020, 08:28   #6
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Re: Yanmar 3GM30 over heat

Is your thermostat working properly?
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Old 26-08-2020, 08:29   #7
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Re: Yanmar 3GM30 over heat

Quote:
Originally Posted by CDR Smith View Post
"My engine had unknown green coolant, I went ahead and flushed it and replaced it with the pink good stuff." Please tell us that you did not use pink water-system antifreeze as engine coolant! I hope you used the proper coolant as called for by Yanmar.
CDR can you explain please as I plan to do a drain / flush soon. I will use Shell Rotella extended life dexcool type coolant.
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Old 26-08-2020, 08:32   #8
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Re: Yanmar 3GM30 over heat

Sounds to me like your thermostat is not not opening up. REmove it and put it in very hot water to see if it opens.
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Old 26-08-2020, 08:37   #9
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Re: Yanmar 3GM30 over heat

Modified for "coolant" doesn't sound very good.

Raw water cooled engines typically run cooler than freshwater 'coolant' engines. This is probably why you are seeing it overheat.

In reality it's probably not overheating, as the 3GM also has a fresh water cooled version, with a few add-ons, but the temp sensor and thermostat on yours will be different, hence the alarms going off.
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Old 26-08-2020, 08:38   #10
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Re: Yanmar 3GM30 over heat

as always with the 3GM .. if you have an exhaust elbow it needs to be checked. when they are clogged you will get a lot of steam.
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Old 26-08-2020, 08:49   #11
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Re: Yanmar 3GM30 over heat

Quote:
Originally Posted by Snowgoose71 View Post
CDR can you explain please as I plan to do a drain / flush soon. I will use Shell Rotella extended life dexcool type coolant.
Water system anti-freeze is not engine coolant. Here's a page from the YM30 manual: https://www.portfoliofotos.com/Busin...5C/i-tHmzPMC/A
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Old 26-08-2020, 09:48   #12
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Re: Yanmar 3GM30 over heat

If you didn't put antifreeze coolant in by mistake, check heat exchanger. There was a silent recall on it awhile back. The new one is bigger because the small one caused overheating.
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Old 26-08-2020, 10:02   #13
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Re: Yanmar 3GM30 over heat

Sorry wrong info. Heat exchange was for yanmar 3ym30, not your 3gm30 Good luck to you.
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Old 26-08-2020, 11:19   #14
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Re: Yanmar 3GM30 over heat

You nailed the cause - the coolant is air blocked which leads to the coolant not flowing properly the heat exchanger. I took a diesel maintenance course and they specifically advised 3GM30 issues are prone to the issue. There is a method to resolve the issue, but frankly I didn't pay attention as I have a 4JH. I second the comments to use the Yanmar approved coolant. Do post the proper method / solution so we all can learn together.
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Old 26-08-2020, 11:29   #15
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Re: Yanmar 3GM30 over heat

After 15 years with a 3FM30F, I think all of the hypotheses previously mentioned are good ones. I had the thermostat go. You mentioned two impellers. Iím only aware of one, but thereís also a water pump driven by belts that circulates the internal coolant that should be checked. Iíve also had a leak at the hot water heater, which is on the coolant circuit. The heat exchanger can get crudded up, itís not to hard to take apart and inspect, but you should get new gaskets before you do that as theyíll probably have to be replaced.

I found the most efficient way to troubleshoot is to take your laser thermometer and follow both circuits step by step. If thereís a big temperature drop or increase upstream and downstream of something where there shouldnít be, or the inverse, that helps isolate.

Good luck.
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