How to change engine coolant water

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AMCarter3
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How to change engine coolant water

Postby AMCarter3 » Wed Feb 21, 2018 11:05 pm

Can anyone provide some guidance on changing the anti-freeze engine coolant water? I need to do this and I have not been able yet to determine where the lowest drain outlet is on the engines.
Mac Carter
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Re: How to change engine coolant water

Postby duetto » Thu Feb 22, 2018 8:18 am

hi mac,

there are multiple drain spigots. i believe there is one behind the oil filter, another under the exhaust elbow, and one on the front next to the water pump. i've used flexible plastic hose to drain coolant into a bucket. if you have the yanmar owner's manual the show them.

i use a heavy duty flush and then flush twice with fresh water.
john & diane cummings
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thinwater
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Re: How to change engine coolant water

Postby thinwater » Sat Feb 24, 2018 1:38 am

I spent decades in the engine coolant formulation industry (chemical engineer), and designed, built, and operated one of the larger facilities.

Unless the system has been neglected, never use flushing chemicals. The people who make them (the tech and testing folks--not the sales department) don't even advise them. They contain corrosive chemicals that remove the passivating film developed by the engine coolant, starting corrosion fresh until the new coolant replenishes the film, which can take several months. They should ONLY be used if you have evidence that the engine is scaled, which should never happen if the coolant is changed on schedule. Flushing chemicals nearly always do more harm than good.

Finally, there are no standards for the safety of flushing chemicals, because the tech folks won't approve them. It's pot luck. That should be a hint. Coolants and stop-leaks have ASTM standards.

Just change the AF. Forget the flush. Forget the freshwater. The only time you flush (water only) is changing formulations, not during maintenance changes, though it does not harm... so long as you flush with distilled water. Flushing with tap water, on the other hand, can introduce contaminants (lime and chloride). So just change it.

BTW, the greatest risk to the marine engnie, by far, is saltwater leaking in through the exchanger. If you actually want to do something good, have the coolant tested for chloride when it is changed. It MUST be less than 150 ppm or you have a real problem.
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Re: How to change engine coolant water

Postby deising » Sat Feb 24, 2018 6:54 am

Drew, that was some interesting info you shared there. Thanks very much.

Where would one go about getting the coolant tested for chloride? Do you know if the pressure in the raw water side is higher or lower than that in the coolant side of the heat exchanger? For salt to migrate in, you would assume the raw waters side is higher.
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Re: How to change engine coolant water

Postby thinwater » Sat Feb 24, 2018 3:45 pm

There are mail-in services and there are test kits:

http://www.acustrip.com/res/pss/PSS-3300.pdf

Seawatr it typically about 25,000 ppm chloride, and the condemning limit for used engine coolant is about 150 ppm, so even trace leakage is a problem.

This is why there is no such thing as extended service or 5-10 year life in a boat; the same engine manufacturer will have different maint advice for generators than boats. Boats get contaminated with salt.
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Re: How to change engine coolant water

Postby AMCarter3 » Sun Feb 25, 2018 11:34 am

Very helpful. I found the 4 drain valves by getting a little coaching from our local diesel experts. The Yanmar manual was useless -- the pictures for the valves are so small they are not legible. I drained the Starboard engine first because it has the long hoses that feed hot coolant to the heater under the entry door steps. I did a water flush and then refilled with Cat DEAC coolant - 50/50.

After running the engine for 30 minutes in gear at 1000 rpm, it seemed fine -- temp gauge ran up to about 170 and held there. HOWEVER cold air was still coming out from the heater coil & fan under the entry door steps. So, I'm assuming there is AIR in the 2 long hoses from/to the engine that feeds hot coolant to the heater. The hoses (outflow and return) are about .75” diameter and at least 16’ to the heater. That’s a lot of coolant. And there are no relief valves where the hoses connect to the heater to release air.

My diesel tech said “Either crack open the hose clamps one of the hoses and bleed the air, OR take the boat out and run it for 30 minutes at high RPM’s (2500-3000). He says the latter usually works to force coolant into the heater and slowly purge the air. I’m thinking the best way would be to run the engine up to normal temp (170), shut it down and then purge the air by cracking open the hose clamps on “return” hose at the engine. However, I don’t know which hose is the return. Any suggestion?
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Re: How to change engine coolant water

Postby AMCarter3 » Sun Feb 25, 2018 12:01 pm

Also, there are 4 drain valves on the Yanmar 100 HP 4JH3-HTE engines: 1) one behind the oil filter (the primary drain); 2) under the exhaust elbow: 3) under the turbo charger unit; and 4) in front under the water pump.
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Re: How to change engine coolant water

Postby thinwater » Sun Feb 25, 2018 11:52 pm

This is why most automotive service stations use a machine that changes the AF by displacement, without draining. Some cars are terribly difficult this way. However, normally the problem slowly clears (air is dispersed in the coolant and comes out the expansion tank). If this were not true, small amounts of air that sneaked in through pump seals would always bind high spots.

If this is a common problem, I would consider installing a high bleed valve. Easier than fighting it.
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