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Old 10-08-2015, 07:09   #1
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Yanmar Slow Coolant Leak

Since the beginning of the season, we've had a very slow coolant leak from the freshwater (antifreeze) side of our 100hp turbo Yanmar coolant system. I just finished pumping out the containment bilge below the engine and evacuated approximately three gallons of greenish brown, oily water which had accumulated over a two month period (1000 miles). I refilled the coolant system which was down only three cups of fluid 24 oz. I can't see any obvious places where the coolant is leaking out, everything seems fine.

My first hunch is the engine water pump is on its way out, but I can't get my head in there to see if it's developed a drip without getting my face ripped off by the fan belts.

Any thoughts or ideas on what the most likely problem might be? It's not so easy on this setup to place the absorbent pads underneath the engine to find the leak.

Thanks in advance for your help.

Ken
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Old 10-08-2015, 07:43   #2
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Re: Yanmar Slow Coolant Leak

The reason for the difference in the amount of water vacuumed out and going in, is that we added maybe two gallons of water to wash out the bilge before realizing that it was a containment bilge.
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Old 10-08-2015, 07:52   #3
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Re: Yanmar Slow Coolant Leak

Some common areas for coolant leaks are endcaps on the heat exchangers and brazing around the pressure cap tube/housing. Could also be a freeze plug. Does your overflow tube from the pressure cap go into the bilge or a tank?

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Old 10-08-2015, 09:45   #4
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Re: Yanmar Slow Coolant Leak

I went looking for the heat exchanger. Thanks to your suggestion, I found two very loose fan belts.... Now fixed. Discovered our throttle cable had multiple cracks in the casing... Now Repaired. Hose clamp on the turbo broken and fallen off... Now replaced and possibly the source of the oil leak.

It's been a busy two hours. We'll clean the entire engine tomorrow morning and order a new air filter. How do people who aren't handy go cruising?

Thanks

Ken
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Old 10-08-2015, 10:08   #5
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Re: Yanmar Slow Coolant Leak

I'd go to an auto parts store and buy a pressure tester, it of course replaces the "radiator cap" and pressurizes the system.
It of course has a gauge on it, that will tell you if you have a leak in your system and how big it is, and you can start looking for external leaks on a cool, not running engine.
It could be as simple as your cap.


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Old 10-08-2015, 10:14   #6
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Re: Yanmar Slow Coolant Leak

It could also be a leak in the flexible hose that runs from the expansion tank to the filler neck. These hoses can get brittle and crack due to heat and time. Often they are poorly attached at both ends, sometimes with no clamp at all. They are often just pushed onto the spout.
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Old 11-08-2015, 08:56   #7
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Re: Yanmar Slow Coolant Leak

Two "hidden" areas for coolant leaks:
1) hot water heater(there's usually a bypass value to eliminate the heater).An internal hot water heater leak will go into the hot water tank. The hot water might smell like antifreeze.
2) the weep hole on the bottom of the water pump may show a rust line where it's leaking and then evaporating.
I've encountered both of these.
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Old 11-08-2015, 09:05   #8
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Re: Yanmar Slow Coolant Leak

We cleaned the engine over the past two days along with the engine containment bilge. Hopefully, now I'll be able to spot the leak. If not, my wife will purchase the radiator pressure tester in two weeks. I've checked everywhere that's been suggested so far.

The leak search has uncovered several other areas in need of service/attention that we've been taking care of.

Thanks
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Old 11-08-2015, 12:02   #9
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Re: Yanmar Slow Coolant Leak

Have similar 100 hp Yanmar. Not sure why you can't see WP which in mine is Port side behind the fan belts etc. Any how most common leak spot is impeller case where the face plate bolts to the housing. There is a rubber O ring on some and if the inside of the face plate is worn you can either turn it around(inside out) or try to scour it with abrasive pad to smooth out. Look there First, don't go looking for zebras.

By the way what was the LAST thing YOU did to the engine, always check the last thing that was fiddled with First. Russ
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Old 11-08-2015, 12:39   #10
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Re: Yanmar Slow Coolant Leak

Rule in or out the head gasket. Oil in water or water in oil is probably the most serious possibility. Siphon off some coolant into jar, look for oil film to separate. Dipstick oil should not appear milky. It could still be the gasket without these manifestations.
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Old 13-08-2015, 13:10   #11
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Re: Yanmar Slow Coolant Leak

I think we sorted out the problem. The leak was apparently water leaking from the generator exhaust hose where it entered the separator. A small amount of engine oil was leaking from the turbo manifold due to a broken hose clamp allowing it to mix with sea water in the containment bilge where it appeared greenish brown in color and oily.

Got the mess cleaned up and will continue to monitor.

Thanks for the help.

Ken
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