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Old 17-04-2021, 19:04   #1
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Coolant drains on Yanmar 4JH3-TE

Coolant on Yanmar 4JH3-TE is low. There was nothing in the overflow tank when we bought the boat and now the level is also below the cap. Problem is I have no idea what coolant has been used. It looks orangish but hard to distinguish orange from pink, red etc. (at least it certainly is not green). I got a Delo ELC (premixed 50-50) and from what I read this is a reasonable coolant for Yanmar. But first, I need to figure out how to flush the existing coolant.

Checking the manual, how many drain plugs there are and where they are is not super clear. From what I read, I *think* there are three but I am not sure. I looked around the engine and identified three potentials. Attaching the photos. Two are on the port side and one is on the starboard side.

Thoughts if these are the right ones? Being no engine expert, I don't want to drain something random.
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Old 17-04-2021, 21:43   #2
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Re: Coolant drains on Yanmar 4JH3-TE

Also found this in the manual. It is a bit confusing and I am not sure if I can map all the drains...
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Old 18-04-2021, 06:12   #3
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Re: Coolant drains on Yanmar 4JH3-TE

Two approaches. One is drain as much as you can find, and then flush by filling with water, running for a few minutes, and draining again. There won't be any coolant of significance left. The other is to find the lowest coolant hose on the engine and loosen it. You could even be really Type A about it and do both. Either way, you'll have an internally clean motor.
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Old 18-04-2021, 06:59   #4
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Re: Coolant drains on Yanmar 4JH3-TE

according to my Yanmar 3JH4E manual Coolant for Yanmar is Prestone dexcool 50/50 for GM vehicles. (change every 5 years)
Don't forget it also cycles through the water heater so need to pull a hose there as well. Otherwise the drain and fill with water flush several times will work.
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Old 18-04-2021, 08:45   #5
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Re: Coolant drains on Yanmar 4JH3-TE

I suspect this is very similar to the 4JH3E which I have. The photo you show is correct and I believe you will only find two, one on port and one on starboard side. It is impossible to drain all the old coolant. Make sure you are loosed or removed the cap on the top of the engine block where you will refill. Then drain.
I donít believe it is worth flushing. It is absolutely critical to use the right antifreeze. The chemicals in the antifreeze are specially designed for the metals in the engine and Yanmar engines do not have sacrificial anodes in the engine. Get genuine Yanmar antifreeze. I would urge you to change out every 2-3 years. The cost of a corroded engine is not worth the economy of pushing this to 5 years.
P.s. I have no commercial relationship with Yanmar but I was involved with the chemistry and manufacture of antifreezes and have seen first hand the damage that can be done to by using the wrong product, including by the previous owner of my yacht using Volvo antifreeze!
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Old 18-04-2021, 09:45   #6
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Re: Coolant drains on Yanmar 4JH3-TE

If it is indeed Dexcool do not mix it with anything but Dexcool unless you thoroughly flush the fresh water system out. Dexcool and other coolants when mixed can form a gel like substance. I would drain out and flush with fresh water and drain again then fill with appropriate coolant. Use the owner's or service manual to determine appropriate coolant.
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Old 18-04-2021, 10:43   #7
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Re: Coolant drains on Yanmar 4JH3-TE

There is also a drain on the front of the engine below the water pump. I also disconnect the hoses to the water heater and blow out the coolant. Fill this hose with new coolant so you do not get an air lock.
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Old 18-04-2021, 12:53   #8
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Re: Coolant drains on Yanmar 4JH3-TE

If you don't see any leak in the engine compartment, check the hoses going into and out of your hot water heater. That is not an uncommon source of a leak.
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Old 18-04-2021, 13:10   #9
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Re: Coolant drains on Yanmar 4JH3-TE

I suspect this is very similar to the 4JH3E which I have. The photo you show is correct and I believe you will only find two, one on port and one on starboard side. It is impossible to drain all the old coolant. Make sure you are loosed or removed the cap on the top of the engine block where you will refill. Then drain.
I don’t believe it is worth flushing. It is absolutely critical to use the right antifreeze. The chemicals in the antifreeze are specially designed for the metals in the engine and Yanmar engines do not have sacrificial anodes in the engine. Get genuine Yanmar antifreeze. I would urge you to change out every 2-3 years. The cost of a corroded engine is not worth the economy of pushing this to 5 years.
P.s. I have no commercial relationship with Yanmar but I was involved with the chemistry and manufacture of antifreezes and have seen first hand the damage that can be done to by using the wrong product, including by the previous owner of my yacht using Volvo antifreeze!
Martin S

I took a Yanmar owners class at an East coast dealer who discussed this in length.
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Old 18-04-2021, 13:17   #10
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Re: Coolant drains on Yanmar 4JH3-TE

I am replacing the water heater on our 2005 H38 because of a leak in the water heater. The engine coolant heating coil in the WH has a small leak, causing the tapwater being pushed back into the engine coolant circuit and overflowing out of the expansion reservoir into the engine bilge. This is in the winter, the engine is not being used, otherwise it would have been the other way around. And if you have a glycol based antifreeze in the engine, .......glycol is a poison! No good tap water.
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