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Old 14-08-2012, 10:11   #1
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Yanmar 3GM30F losing coolant

The engine has hoses going through the water heater and I think there may be a small leak in the WH exchanger. If I turn off the freshwater pump and let the engine warm up, I get a small amount of water pressure in the hot water line. Just a burp of water, but it's there, and will build back up if I wait a few minutes. I lose ~ 3 cups of coolant after an hour or so of engine operation. Will dye hurt the engine? Can it connect the 2 hoses together, (loop), taking the WH out of the circuit?

Any suggestions?

Thanks.
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Old 14-08-2012, 10:14   #2
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Re: Yanmar 3GM30F losing coolant

Certainly you can connect the two hoses together.
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Old 14-08-2012, 10:20   #3
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Thanks DeepFrz - I was pretty sure about the loop, but wanted to confirm. It's my first boat, purchase just six weeks ago - steep learning curve... Can I add dye to the system without harming any components?

Regards.
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Old 14-08-2012, 10:45   #4
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Re: Yanmar 3GM30F losing coolant

I'm not sure about the dye so I can't recommend it unless you are going to flush the engine and change the coolant in the system after you find the leak. Probably a good idea to do that anyway as it is a new to you boat.
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Old 14-08-2012, 12:22   #5
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Re: Yanmar 3GM30F losing coolant

If you are getting anti-freeze into your water heater, do not drink the water
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Old 14-08-2012, 12:33   #6
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Have not, didn't plan to until the leak is corrected. I need to flush the fresh water tank and lines anyway. Thanks
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Old 14-08-2012, 13:07   #7
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Re: Yanmar 3GM30F losing coolant

If the water circuit is Potable(drinkable) then just use a few packets of Unsweetened Coolaid powder which will be very safe and will provide the tell tail to trace the leak.
and yes of course you can loop the hoses.
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Old 14-08-2012, 15:47   #8
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Re: Yanmar 3GM30F losing coolant

If you loop the hoses to the water heater and the leak goes away, then the water heater coil is leaking. As others have said, don't drink the water until it is fixed.

But I would suspect the raw water heat exchanger as the source of your leak, not the water heater. You can buy a pressure testing kit at all auto parts stores. Take off the end caps of the heat exchanger first. Pressure up the fresh water system and look for water oozing out of the tubes. It could also be the seals on the fresh water pump. Look for leaks around its shaft when it is pressured up.

David
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Old 14-08-2012, 16:00   #9
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I'm going to pull the WH hoses off the engine and turn on the FW pump to see if any water comes out/through the WH exchanger. I'm really hoping its not the engine heat exchanger... Very costly. Thanks for the tips.
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Old 14-08-2012, 19:46   #10
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Re: Yanmar 3GM30F losing coolant

Heating water causes the water in the water heater to expand a little bit. So that bit of pressure is from thermal expansion. The fresh water system is at 30-40 psig. Most radiator caps vent at 10-13 psig. In other words the engine pressure is lower then the fresh water pressure, so a leak in the water heater coil goes the other way.. to the engine.

Loss of coolant can be a drippy hose, a blown head gasket or maybe a crack in the raw water heat exchanger.
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Old 14-08-2012, 21:55   #11
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Well, that's that. I don't think it's the head gasket, no white smoke, starts right up, runs well. Can a radiator shop repair the exchanger or am I stuck buying a new one?
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Old 14-08-2012, 21:58   #12
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Re: Yanmar 3GM30F losing coolant

Don't assume anything. Check the water heater and the exchanger and see what the results are before you make any decisions.
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Old 16-08-2012, 13:48   #13
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I have a pressure tester and plan to test the system. What PSI to I pump in?
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Old 16-08-2012, 15:50   #14
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Re: Yanmar 3GM30F losing coolant

Well its not so much how much pressure, but does it hold pressure. So 7 psig (1/2 bar) would be fine.. Pump it up, record pressure wait half an hour and check to see if the pressure drops. If it drops you have a leak somewhere. could be a hose too.
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Old 16-08-2012, 21:55   #15
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Turned out to be the water heater, looped a short hose on the engine and pressure test held. Ran the engine and fluid level remained the same. I'll know for sure next time I take the boat out. Thanks again for all the replies. Regards.
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