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Old 07-07-2021, 08:00   #1
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How much coolant loss is normal/acceptable?

I have a 17 year old Yanmar 3JH4E with around 1,600 hours on it.

If I motor for, say, 8 hours, I can expect the level of coolant in the reservoir to be 1/4" lower when cold the next day.

What, if any at all, is an expected or acceptable rate of coolant loss?

No coolant detected in oil, no obvious leaks, so likely some leak in heat exchanger perhaps?

FWIW I have not yet accurately measured the rate of loss, above is a swag.
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Old 07-07-2021, 08:25   #2
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Re: How much coolant loss is normal/acceptable?

I can't remember the last time I had to add coolant, near zero loss.
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Old 07-07-2021, 09:36   #3
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Re: How much coolant loss is normal/acceptable?

Same here, zero loss even before I rebuilt the top end. I would track the source of the the leak. If itís in the head then it should get dealt with sooner than later.
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Old 07-07-2021, 15:02   #4
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Re: How much coolant loss is normal/acceptable?

We did have coolant loss, about 3 yrs. ago, now. Normally there is none.

It was from the heat exchanger. Jim saw it right away, upon starting the engine, and looking astern. Our coolant is green, and it was quite obvious on the water.

We had to replace the whole exchanger, rather than repair the inner bits, because of marketing issues, and wanting to get the engine functioning quickly (living on the hook).

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Old 07-07-2021, 15:11   #5
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Re: How much coolant loss is normal/acceptable?

Pressurize the system with a test kit.

Mine was stable, then I replaced the water heater and the many many feet of hose between it and the engine.

I’m still slowly getting air out.....
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Old 07-07-2021, 15:45   #6
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Re: How much coolant loss is normal/acceptable?

How much coolant loss is normal/acceptable? None
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Old 07-07-2021, 17:57   #7
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Re: How much coolant loss is normal/acceptable?

After replacing HX and testing oil and exhaust gasses, it turned out to be my water heater
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Old 08-07-2021, 12:14   #8
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Re: How much coolant loss is normal/acceptable?

I think you may be chasing an non existing problem. Check it and see if it drops another 1/4". Realizing liquid doesn't expand metal does. It maybe just expansion and it shouldn't be filled to the very top.
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Old 08-07-2021, 14:18   #9
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Re: How much coolant loss is normal/acceptable?

i had a truck that needed coolant every month or so. went thru this for years and finally had the intake manifold resealed and it has zero coolant loss since then. a small leak is tolerable until you fix it .. but not ideal
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Old 08-07-2021, 14:28   #10
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Re: How much coolant loss is normal/acceptable?

Had a very small leak once due to a gasket on the thermostat took a while to find !
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Old 08-07-2021, 14:44   #11
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Re: How much coolant loss is normal/acceptable?

Coolant is not normally consumed in use and there should be no coolant loss.

You might see the level go down the first couple times you run the engine after draining and refilling it because of air in the system but it should soon stabilize.
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Old 08-07-2021, 15:51   #12
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Re: How much coolant loss is normal/acceptable?

Does your installation have a “puke” tank mounted? If you fill the heat exchanger and run the engine to fully heat it up and heat sink the whole thing the coolant will expand and drain out the little vent under the spring seal on the pressure cap. You loose that amount without a recovery bottle ( another name for it).
With the system full and the puke tank about 1/4 full the fluid will go back and forth as needed and the hx will stay full to the top. These are available as aftermarket from auto supply if your engine manufacturer doesn’t make one.
Mount somewhere in front or off to the side of the hx and run the included tube into the bottom of the tank and it is good to go.
Maybe once a year it might get a little water or coolant added to the puke tank.
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Old 08-07-2021, 21:17   #13
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Re: How much coolant loss is normal/acceptable?

The side effect of coolant loss is if leakage is into the bilge it manages to moisten your LPG gas detector. Glycol is a hydrocarbon and thus the detector will burn it and shut off your gas supply. Most inconveniently, it will choose the time it creates the most chaos, never straight away.
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Old 09-07-2021, 03:44   #14
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Re: How much coolant loss is normal/acceptable?

Quote:
Originally Posted by flightlead404 View Post
. If I motor for, say, 8 hours, I can expect the level of coolant in the reservoir to be 1/4" lower when cold the next day.
What, if any at all, is an expected or acceptable rate of coolant loss?

FWIW I have not yet accurately measured the rate of loss, above is a swag.
1/4” lower coolant level in res from engine cold or hot level? Level will drop when cold. But I figure your adding. You don’t need to measure the loss, How much are you adding, or have added (approx)? closed loop systems shouldn’t need topping off. If this is the first time and your not seeing anything evident, check the water pump weep hole.
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Old 09-07-2021, 07:26   #15
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Re: How much coolant loss is normal/acceptable?

To clarify, as apparently my original post wasn't clear, the level in the expansion tank/reservoir/puke tank is what I'm seeing change.

Coolant level in the heat ex itself is always right at the top.

I'm always checking this cold. ie check in the am before start, run for a day, check then next day before start.

There are no leaks I can see, into the bilge or elsewhere on the motor.

I recently, ie couple months ago, changed the coolant pump, a few hoses, and descaled the heat ex. idk if it was happening beforehand as the boat is new to me.

It had not occurred to me the issue could be the water heater. For those that mentioned that, could the water heater leak internally, ie coolant into the hot water side? Otherwise I'd assume that leaks would be obvious from external inspection of the heater and hoses?
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