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Old 25-04-2011, 09:08   #1
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Engine Coolant Loss

I have a new Yanmar 4JH4TE that was installed in my boat roughly a year ago. Since installation, the coolant overflow tank level has been consistently falling approximately one inch every 20 hours of use. There are no signs of external leaks anywhere in the cooling system, including my hot water heater and elsewhere. There are also no signs whatsoever of water ingestion by the engine. I have added approximately one gallon of cooland over the last year.

My installer came out and performed a coolant system pressure check. While there was a very slight drop in pressure over about 15 minutes, we believe that to be caused by leaks in the pressure check apparatus. The technician indicates that the drop in coolant level could be caused by an air bubble in the water heater coolant loop that is slowly being replaced by coolant. His recommendation is to see if the problem disappears over time. He also indicates that this problem can be caused by a leak in the hot water heater heat exchanger, but the coolant level in my previous engine (4JH3TE) never dropped at all and there doesn't appear to be coolant in the hot water. It would also be quite a coincidence if my water heater failed exactly at the time the new engine was installed. No corrective action was taken, and I am somewhat skeptical that the indications would continue for this length of time. Any recommendations or advice on nailing the cause down would be appreciated.

Thanks,

Bob
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Old 25-04-2011, 09:19   #2
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Re: Engine Coolant Loss

Check for exhaust gases in the header tank - you can get kits at your local motor-factors. If you find combustion products there, you have a blown headgasket.
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Old 25-04-2011, 11:23   #3
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Re: Engine Coolant Loss

well, you can easily confirm/deny the water heater by simply disconnecting it from the cooling circuit for a period of time and see if you still loose coolant. If the problem persists, then it isn't the water heater; if problem stops, then it is.

Other typical problems that can lose coolant: the main heat exchanger, cracked exh. manifold, blown head gasket.... If you have no evidence of any leaks anywhere, and no water in your oil, then that indicates that the lost coolant is being pumped overboard along with the exhaust, so start by suspecting areas where the coolant is close to either sea water or exhaust gases.
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Old 25-04-2011, 13:50   #4
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Re: Engine Coolant Loss

Thanks for your comments. I had planned to disconnect the heater hoses if the problem continues. I am not familiar with the "local motor-factors" and their kits. Is that something I can pick up at a local automotive store. Can you explain further? Also, I assume you are refering to the coolant header/overflow tank. It would be good to eliminate the possibility of a head gasket issue.

Thanks again!

Bob
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Old 25-04-2011, 14:05   #5
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Re: Engine Coolant Loss

Bob, if the leak in the head gasket was in a place that put exhaust gases into the header tank (the place where your radiator cap screws on), then you would normally be getting MORE water into the recovery bottle (aka: overflow tank), not less, because if the break is letting combustion gas into the water galley, then it would usually over-pressurize the coolant system, and that pressure causes coolant to fill the recovery bottle when the engine is running. Not always....

Checking as Old Nemesis suggested isn't out of the question, but your symptoms don't indicate that kind of issue. IF the problem is the head gasket (which isn't likely on a new engine), then it's more likely a problem near the exhaust manifold. You could also just have a bad exhaust manifold gasket, loose manifold bolts. But all that is unlikely with a new engine.

Start by ruling out the water heater. Next, I would remove the heat exchanger and have it pressure tested by someone who has reliable test equipment. Rule out the obvious stuff first.
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Old 25-04-2011, 14:18   #6
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Re: Engine Coolant Loss

What about the heat exchanger? Might your coolant be leaking into raw water then out the exhaust?

Rich
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Old 25-04-2011, 15:23   #7
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Re: Engine Coolant Loss

Hey, if the engine is only a year old then its under full warranty. Install a valve in the engine to shut off any external items such as a Red Dot or hot water heater. If the engine continues to loose water contact your Yanmar dealer before the warranty is out
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Old 25-04-2011, 15:32   #8
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Re: Engine Coolant Loss

There was another similar thread to this a couple of years back. I suggested, as a cheap starting point, trying a new pressure cap on the cooling system.

It worked. Maybe it would work again?
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Old 25-04-2011, 15:48   #9
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Re: Engine Coolant Loss

Just an added note: The engine technician told me that a heat exchanger leak would cause salt water in the coolant since the pressure on the salt water side is higher than the fresh water side.

Bob
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Old 25-04-2011, 15:58   #10
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Re: Engine Coolant Loss

I hope you didn't pay the guy who said he was testing your system with faulty test equipment. The system should be able to maintain pressure over time. You certainly should not see a drop in pressure in 15 mins. And as far as pressure difference goes, The coolant side of the system would be at a higher pressure than the sea water side. Otherwise, why would you have a pressure cap on the coolant side of the engine cooling system with a warning about releasing the cap when the engine is hot? Sea water flows through the system in a very low pressure circuit.
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Old 25-04-2011, 16:14   #11
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Re: Engine Coolant Loss

Curious: how many engine hours are we talking about since it was new to use that gallon of coolant?
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Old 25-04-2011, 19:23   #12
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Re: Engine Coolant Loss

The engine used a gallon of coolant over about 110 hours. The needle on the pressure guage barely moved over about 10 to 15 minutes. A slight pressure loss can be espected with any of that type of equipment.

Bob
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Old 25-04-2011, 19:26   #13
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Re: Engine Coolant Loss

Just thinking further. That seems to be a good point on the seawater being at lower pressure.

Bob
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Old 25-04-2011, 20:28   #14
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Re: Engine Coolant Loss

There should be no drop in ten minutes.

Where are you adding coolant?

Engine or overflow?
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Old 25-04-2011, 21:13   #15
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Re: Engine Coolant Loss

I am adding coolant in the plastic overflow tank. The needle movement over a 10 to 15 minute period was barely discernable. I am really impressed with the knowledge base on this forum. It is a great resourse

Bob
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