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Old 03-10-2023, 10:13   #1
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Engine coolant level drops (Yanmar 3GM30F)

Is there a typical amount of engine coolant that a 3GM30F with approx. 2000 hrs would use?

I noted the coolant level in my overflow tank, then motored for about 7 hours over two days, and the level is down somewhere around 1/8"-1/4". I'd been noticing these small drops in overflow tank level and wondered whether it was normal.

I've looked at the oil and it seems fine and no noticeable white smoke.
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Old 03-10-2023, 11:03   #2
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Re: Engine coolant level drops (Yanmar 3GM30F)

circulation pump moves antifreeze at a higher pressure than the water pump">raw water pump. When pin holes eventually form in the tubing of the heat exchanger, this forces a small amount of antifreeze into the raw water side, which is discharged with the raw water out the exhaust.

Keep a close eye on the levels, this will get worse over time. It will not manifest itself in the oil color or levels, or in the bilge because that is not where it is going. It won't steam or change exhaust color.
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Old 03-10-2023, 12:51   #3
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Re: Engine coolant level drops (Yanmar 3GM30F)

have you got a Hot water tank ?
have you drained the circuit recently ?
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Old 04-10-2023, 07:20   #4
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Re: Engine coolant level drops (Yanmar 3GM30F)

I do have a hot water heater that is heated by engine coolant. It is a new unit put in at the beginning of this season, so all the coolant was drained and replaced as part of the install.

Unfortunately I wasn't paying attention to this before now, so can't say whether anything changed going from the old heater (which had a wiring meltdown) to the new heater. Of course my big concern is if the new heater was faulty and has a leak. We don't drink tank water but do use it for washing up.

On a slightly related note, I have to periodically top up the engine coolant on both my cars (2016 & 2018), so I know that some engines do use coolant.
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Old 04-10-2023, 07:59   #5
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Re: Engine coolant level drops (Yanmar 3GM30F)

We just replaced our hw tank as well. For the next few times motoring we did have to top up coolant. It takes a little while to "burp" the tank and hoses.
I would also check those hose connections to ensure no leaks
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Old 04-10-2023, 08:00   #6
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Re: Engine coolant level drops (Yanmar 3GM30F)

Realistically you shouldn't be loosing any coolant over time. but if you did change the water heater recently, there are good chances that there was air in the system after the change and when running the engine will eventually burp itself free of the air. When it does, it will suck up some coolant from the overflow tank once the engine stops running and cools down
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Old 04-10-2023, 08:27   #7
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Re: Engine coolant level drops (Yanmar 3GM30F)

For so e unknown reason my expansion tank always goes down. But the level in the engine always stays full
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Old 04-10-2023, 08:50   #8
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Re: Engine coolant level drops (Yanmar 3GM30F)

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Originally Posted by sailorboy1 View Post
For so e unknown reason my expansion tank always goes down. But the level in the engine always stays full
LOL!!!
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Old 04-10-2023, 10:07   #9
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Re: Engine coolant level drops (Yanmar 3GM30F)

You need to check level before/after when cold. Or hot... as long as it's the same situation.
Is it possible your "radiator" cap is defective, or the wrong pressure rating, causing coolant to be blown out the overflow?
or:
-heat exchanger leak as noted above.
-Small head gasket leak, this can go into the oil or out the exhaust.
-Check your oil for bubbles.
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Old 04-10-2023, 10:23   #10
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Re: Engine coolant level drops (Yanmar 3GM30F)

I have the same engine in my Pearson, I would check the cap first, cheap and easy.
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Old 04-10-2023, 13:58   #11
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Re: Engine coolant level drops (Yanmar 3GM30F)

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Originally Posted by leecea View Post
Is there a typical amount of engine coolant that a 3GM30F with approx. 2000 hrs would use?

I noted the coolant level in my overflow tank, then motored for about 7 hours over two days, and the level is down somewhere around 1/8"-1/4". I'd been noticing these small drops in overflow tank level and wondered whether it was normal.

I've looked at the oil and it seems fine and no noticeable white smoke.
The answer is NONE. Not at 100 hours, not at 2000 hours, not at 10,000 hours. An engine has no way of "using" coolant that should be tolerated.

If coolant is leaving the system, it is leaking out somewhere. It might be leaking out of the engine into the pan below it. Are there any traces of coolant there? Is your engine and the space under it clean enough that you would SEE a coolant leak? If not, make it so.

If not escaping into the engine room, it is leaking out of the engine into the oil, or into the cylinders, or into your water heater. Or, possibly out into the raw water.

If you have a leak out into the sea water cooling circuit, you will also get some seawater back into the coolant. This can be found with a coolant analysis looking for levels of chloride.

You can get small leaks of coolant into the oil that are not visible. If you run the engine at operating temperature, for significant time, the water will boil out of the oil, and the remaining glycol does not show as an emulsion. An oil analysis is the best way to find it if it is there.

On most wet exhaust boats, you will never see the plume of white vapor you get with a car that is burning coolant. The water sprayed into the exhaust pretty efficiently "scrubs" out the glycol from the exhaust gas. If it is a large leak, you can usually tell by collecting a sample of the exhausted water and checking for the distinct oder of hot coolant.

The most important one to check RIGHT AWAY is your water heater. Ethylene glycol is a poison and should not be treated lightly. If you have coolant in your water system it is likely you would be able to detect it by taste, it is distinctly "sweet", but I would not count on that being enough to keep you safe.

The gold standard for determining if you have a leak is a pressure test. Either get a cooling system pressure tester, or get somebody in who has one.
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Old 05-10-2023, 14:22   #12
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Re: Engine coolant level drops (Yanmar 3GM30F)

separate the hot water tank (close the 2 valves or install them), and check if the level continues to drop ...
if the level is stabilized, that's where the problem comes from!
it is common after installing a tank or draining the circuit, that a large air bubble remains stuck
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Old 13-10-2023, 10:42   #13
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Re: Engine coolant level drops (Yanmar 3GM30F)

After replacing the coolant in my diesel, it took a while for the air to circulate out of the system. I would notice the level dropped and would add some more coolant. It took a couple of long engine runs for the air to finally clear out.

The same would apply for the HW tank removal

Months later I did notice a continuous drop in coolant level. it was attributable to an internal leak in the coolant/raw water Heat exchanger. I ended up installing a new HX and everything has been OK to date.

my two cents.
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Old 13-10-2023, 20:09   #14
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Re: Engine coolant level drops (Yanmar 3GM30F)

I wouldn’t be loosing a lot of sleep over an eighth inch. I would keep an eye, but I always check water, oil, belts and packing glad before getting underway. And yes, the cap sometime guilty and a quick cheap fix. If you do find that you need a heat exchanger you can save a LOT of Money. Go to MR Cool marine heat exchangers. They have a huge selection. They are very good quality, easy to deal with and Soooo much cheaper than Stock OEM. I have used them on 3 different engines over the years with very good luck.
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