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  #11  
Old 02-05-2013
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Re: Engine over temp at idle

One item not mentioned is the engine thermostat? Had a similar tempeture swing on our last boat equiped with a Yanmar single cylinder Thermostat was worn and sticking
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Old 02-05-2013
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Re: Engine over temp at idle

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Originally Posted by Minnewaska View Post
If my silicon grease, you mean the sticky stuff in a tube, that may not be a great idea. It should certainly help prime the pump, but I would worry what happens to it as globs move through the heat exchanger or block. Glycerin or dish soap, which are less viscous, are the norms.

Running the impeller dry will do damage, even if you can't see it with the naked eye. The vanes could let go on the next run. Best to always replace an impeller that you know you ran dry for more than a few seconds to prime.

Could be a blocked intake, but it would be very unusual. Blockages in the exchanger are more common. Or, as I said, if the seawater strainer has a leak, it may not allow for the suction necessary to draw the raw water.

Good luck.
This engine is direct sea water cooled- no heat exchanger- sea water goes right throught the block. I smeared the grease but no globs. One of the Yanmar manuals states to grease the surfaces of the impeller and pump housing. You are probably right to replace the impeller after a dry run. I'll let you know what I find. The way I attach the fresh water bucket I would actually have water pressure throug the raw water strainer all the way to the sea water pump. A leak should have shown up as at least a drip- but I had nothing. One thing my yanmar has a Kanzaki V-drive (that has an oil transmission cooler), what happens is the raw sea water suction side of the pump pulls the water through this cooler then into the raw water pump. The oil cooler looks to be an aluminum housing- it does not leak, but could be clogged. I will know more once I start tracing lines for cloggs. Figure I'll just start pulling hoses and doing a blow test till I find a restriction.
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Old 02-05-2013
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Re: Engine over temp at idle

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Originally Posted by SawWhet View Post
One item not mentioned is the engine thermostat? Had a similar tempeture swing on our last boat equiped with a Yanmar single cylinder Thermostat was worn and sticking
I am thinking that thermostat and housing is an area of interest as they say. I am amazed the yanmar thermostats actually work seeing they are really small, and seeing my engine sends raw sea water through it makes it even more amazing. I replaced the thermostat about two years ago and the stat and housing was full of white material- think it is calcium carbonate that precipatates out of sea water when heated.
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Re: Engine over temp at idle

I still find an intake blockage to be the least likely, but good luck. Could happen, I suppose. If you don't already have wire reinforced clear hoses, you might consider replacing them while you're at it. Much easier to see flow when the engine is running and to eliminate the blockage theory.
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Re: Engine over temp at idle

Quote:
Originally Posted by Minnewaska View Post
I still find an intake blockage to be the least likely, but good luck. Could happen, I suppose. If you don't already have wire reinforced clear hoses, you might consider replacing them while you're at it. Much easier to see flow when the engine is running and to eliminate the blockage theory.
Good Point. My hoses are just standard black engine cooling hoses. I considered installing wire reinforced (that is really what a suction hose should be) but the ones I have seemed to have worked well. Maybe the hose is colasping when the raw water pump is pulling suction. I will check this.

Good point as everything may show up clear- but the hose collapses when you run the pump. Maybe that is the problem the OP is having. At idle the suction would not be enough to collapse the hose, but at high rpm the suction increases on the suction hose and the hose could collaspe.
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Old 02-06-2013
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Re: Engine over temp at idle

The suspense of what was causing the overheat made me work on the boat till dark yesterday. Found the problem. it was a single yanmar engine cooling bypass hose (about 4 inches long) that runs from the cooling water inlet to the engine, then to the themostat housing.

This hose will bypass all the raw sea water so that it does not enter the engine block. Once at the thermostat housing, the water is directed to the exhaust manifold then to the mix elbow. This hose (about 5/8 inch ID) was packed solid with material. I think the material was oxidized zinc anode from the engine.

I think what happened is that the first thing I did was removed and cleaned the engine block zincs. When I removed these there is a crusty deposit on them and some drops into the engine block- not much you can do to prevent, maybe could be sucked out with a wet/dry vac. After cleaning and replacing zincs, I went to the raw water pump to change the impeller. I think when I took the discharge hose off the pump (needed to remove to open it up as access is tight), the water from the block, along with anode oxidation drained to the pump discharge hose. After impeller replacement, I started engine. The zinc deposits were then pumped into the bypass line and clogged it. Since on engine start up, the thermostat is closed, all cooling water goes to the bypass line. Once the engine is warm, the thermostat opens, and water would go through the engine.

To prevent this, in the future I will first change the water pump impeller. Run the engine, then check the zincs, then open the thermostat and check for deposits they may have gotten trapped.

I still plan to install new impeller and open up thermostat housing to inspect.
But for now, she is purring like a kitten.
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Old 02-11-2013
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Re: Engine over temp at idle

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Originally Posted by casey1999 View Post
I still plan to install new impeller and open up thermostat housing to inspect.
But for now, she is purring like a kitten.
Changed out the raw water pump impeller (the one that was replaced looked new, but changed it just in case). Installed new thermostat. Old stat looked good so will keep as spare. Very little deposits on the thermostat and stat housing. Engine running good.
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Old 03-13-2013
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Re: Engine over temp at idle

check for air leak in raw water filter, bits of impeller in heat exchanger.,,If this is the problem, you could ruin a new impeller!
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