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  #1  
Old 11-24-2013
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Hot Water Heater Leaking Coolant

I had a yard replace my original hot water heater on my 1986 S/V, the summer before last. The new unit was a 6gal Kuuomo heater tied into my engine (Yanmar 3GM30F) coolant system. Immediately after the install I had coolant leaking from the engine pipe to hose connections which I later determined was not because of bad connections but because there was too much pressure in system...which led to one over-heating alarm incident...quickly resolved by lowering RPM...and then having another mechanic to purge the system from a suspected air block?, or whatever, but it seemed to solve the issue. EXCEPT, I continued to have nagging problem of losing small amounts of coolant seen on the engine house floor...and coolant being pushed to the reserve canister, but not being pulled back into the engine when cooled down. Often, I would just pour the contents of the reserve can back into the radiator, and just add several ounces of coolant...and the engine always got me where I was going.
Now that I have had time to do some detailed investigation myself. I have found a small coolant leak that appears to be coming from the bottom of the hot water heater. I say "appears" because total access to the heater is impossible. I have confirmed that the leak is not from any of the ports because all those are easily accessed on one side of the unit...it is the opposite side near the bottom where it looks like coolant can be seen oozing from seams in the tank cover (aluminum). Since removing the tank in this typically difficult location under the cockpit deck will be a major effort of putting your body into pretzel-like shapes while removing hosing, nuts, and wires, I'm trying to get some advice on what may be happening before I have to escavate.
Questions. What would cause coolant leak from within the tank? Could the high pressure from the minor overheat alarm incident summer before last have compromised the heating element inside the tank to cause the leak? Could it be related to the push of coolant to the engine reserve canister?
and is it sign of poor quality unit, faulty installation, or defective product?

Thanks for any guidance.
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Old 11-24-2013
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Re: Hot Water Heater Leaking Coolant

BTW, I have checked and there is no coolant leaking from anywhere on the engine block or engine connections. the hot water heater is located aft of the engine behind a bulkhead, and I can see the line of coolant leaking from the direction of the water heater...which by way of the engine house floor is uphill from the engine compartment.
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Old 11-24-2013
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Re: Hot Water Heater Leaking Coolant

It seems from the little information you gave, the water heater was replaced by idiots. The very very first thing they should do is "burp" the heat exchanger. the engine pressure is not enough to cause metal tubing to burst since the radiator cap on the engine is also a type of relief valve and lets the overflow and high pressure "spill" into the overflow tank.


Where the engine coolant lines connect may be the problem since the end of the hose may be just inside the sheet metal cover of the water tank, it could also be loose pipe thread to hose fittings where they tighten into the tank. Also.. a small amount may be tracking down the hose to the engine, since it's uphill from the engine too.

You did not call the people that did the work and demand a proper and safe installation? The whole install was faulty!
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Old 11-24-2013
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Re: Hot Water Heater Leaking Coolant

Denise, thank you. I am very careful to blame the yard before I know exactly what has caused the problem...even though I arrived with a trouble-free hot water heater/coolant system, and left with continuous problems. And did I say they screwed up nearly every other project they did...and charged me for their services!
When I get to the bottom of all this, I will inform where I had the work done.

Ya know when you don't keep your boat in the same place, it is often impossible without a huge effort to return the boat to the yard where the work was done and ask them to correct their blunders. Even more of an issue is my reluctance, in those circumstances, to return the boat to the source of the incompetence and give them another chance to cover their mistakes or cause additional damage.
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Old 11-25-2013
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Re: Hot Water Heater Leaking Coolant

Pictures could be helpful...

Regarding the coolant overflow container; it may be mounted too low with respect to the engine. The top of the pressure cap should be level with the lower third between the add, and full line on the overflow container.

Both problems could also be the pressure cap. Normally they release pressure at 14PSI. I also believe that there is a difference between caps that work with overflow containers, and those that vent into the bilge.
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Old 11-25-2013
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Re: Hot Water Heater Leaking Coolant

Thanks Herlihy, I'll check the placement of reserve container.

Also, correction, the new hot water tank is made by Kumma.

I did replace the heat exchanger cap.

I will send some pics later.
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Old 11-26-2013
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Re: Hot Water Heater Leaking Coolant

On cooling systems with an atmospheric catch tank, the radiator cap has two seals. The top one, which seals to the body of the expansion tank, and a lower one, which opens at 14 PSI. The excess coolant then runs into the catch tank.

On cool down, this is where a small sprung plate in the base of the cap comes in. It opens and allows coolant to be drawn back into the expansion tank.

Things that can and do go wrong are :

A kink or collapse in the hose between expansion and catch tanks, so water goes one way but not the other.

A bad spring or seal in the "coo down" valve in the radiator cap.

A bad seal on the radiator cap top seal

NB : all hose and other connections should be able to hold the lift pressure of the radiator cap. If not, either the connections, or the cap, are faulty. Ability to hold pressure is essential to proper cooling system function, as otherwise you can get localised boiling at hot spots in the engine, and generation of lots of gas.

I don't believe the exact height of the catch tank with reference to the expansion tank is important, as the system will generate plenty of suction on cool down. The expansion tank should be the highest point of the cooling system, though.
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Last edited by MarkSF; 11-26-2013 at 03:26 AM.
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