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Old 23-06-2013, 11:30   #1
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Join Date: Jul 2009
Location: Ontario, Canada
Boat: Niagara 31
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Engine Overheating: Problem & Solution!

Last winter, I drained the antifreeze from my engine and removed the heat exchanger in order to give it a good clean.

I replaced it, filled up the anti-freeze EXPANSION TANK and went sailing for the FIRST time this season (there's been lots of problems this year !). On my way out of the harbour, just, luckily, as I had reached open water, the engine started to RAPIDLY overheat. I quickly turned it off.

I sailed around until the engine had cooled down, and then made it back to 100' of my slip before I had to turn the engine off again. I docked OK (single-handed !)

At the slip I started to think what could be the problem. I'd replaced the muffler this spring, but water was coming through the exhaust pipe and the ammeter was showing a charge, i.e. the raw water side was OK, and the V belt was OK. So it must be the Coolant circulation.

To cut a long story short, there was not enough antifreeze flowing around the engine because the anti-freeze had not flowed from the EXPANSION TANK to the HEADER TANK due to the filler cap not opening the valve. (It wasn't immersed in fluid, so how could it !). I learnt from an old time mechanic, that you should always make sure the HEADER Tank is full by removing the filler cap and directly filling it as necessary. Leave the cap off for a short while and run the engine, and top up as necessary. Then replace filer cap and fill up EXPANSION TANK. I had to undo my feed tube from the EXPANSION to the HEADER as it had an airlock in it.

Engine now runs OK !!

Hope this helps other people in the future !

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Old 23-06-2013, 12:12   #2
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Join Date: Feb 2013
Posts: 147
Re: Engine Overheating: Problem & SOLUTION !

one tip from my experience , as much coolant you take out put it in a can measure the quantity . when you fill up with new put the same quantity then you are sure that you have minimized your airlock in you cooling system

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Old 23-06-2013, 12:24   #3
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Re: Engine Overheating: Problem & SOLUTION !

Pretty basic stuff. The fresh water side isn't full until the thermostat opens and the coolant circulates. Most engines have an air bleed either internally or externally. Chuck
Chesapeake Bay, ICW Hampton Roads To Key West, The Gulf Coast, The Bahamas

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Old 25-06-2013, 21:35   #4
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Quality coolant last about five years. When replacing it I take the thermostat out and check its function in hot water. Then I pour fresh coolant through the thermostat opening into the engine until it tops off. Next I re-install the thermostat and connect the hose to the heat exchanger. Then I top off the heat exchanger through the filler cap opening. After closing the HEx cap I fill the expansion tank to the minimum mark. Now I start the engine and check the temperature change on all hoses by touching them. After all circuits have reached operation temperature I cut off the engine and let it cool down. When the engine is cold I check again the coolant level in the expansion tank and fill it back to the min level mark if needed. My engine is a Yanmar 3JH2.
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engine, overheating

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