Yanmar 2 qm 15 overheating mystery - SailNet Community

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  #1  
Old 05-24-2009
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Yanmar 2 qm 15 overheating mystery

We have a 1982 Bayfeild 32C with a Yanmar 2QM 15hp raw fresh water cooling system that's over heating.

At the dock the motor pumps water without a hitch, motoring down the bay there are no problems.

It seems that as soon as we sail, invoking heel, the motor wont pump water on the start, and faithfully overheats.

We've had this problem since last summer, as a result we've replaced the muffler, thermostat, impeller and the water strainer.

I've sailed for 40 years on many different boats, learning alot about water cooling systems on primarily atomic IV's.

To resolve this issue (like today) we take all the hoses off to source a problem, put it all back together and it pumps water once again.

Any advice or knowledge of why this motor might stop pumping water once the bot has heeled would be greatly appreciated. This is a weird problem that seems stupid to even describe!

thanks
Nick
Collins Bay Marina,
Kingston, ON Canada
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Old 05-25-2009
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Nick,
I suspect that water is leaking back through the water pump causing the pump to loose it's prime ? When you replaced the impeller did you resurface the cover plate? also look at the inside face after removing the impeller and look for scoring on the back wall of the pump. I suppose you could check this by removing the lower hose and over a period of time see if the water drains out of the engine back through the pump. If all surfaces are flat and smooth it should not. These little $385 pumps can be real finicky.
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Old 05-25-2009
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I think Bill is right on track. It sounds like the pump has excessive clearances and is losing its prime and not able to reestablish it unless the suction is flooded. Either rebuild it (including filing the cover plate smooth) or replace it.
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Old 05-25-2009
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If in need of parts or a replacement I give these guy's the thumbs up!
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Old 05-25-2009
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thank you so much, we're looking into a new pump now, and discussing it with our local marine mechanic, ill be sure to keep you informed of how things go
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Not sure about the 2QM, but on my 2GM, it is possible to turn over the cover plate, on the raw water pump, if it is scored.

I had the same trouble as you, it would only overheat after sailing / heeling. Never did it at the / from dock. It was losing it's prime, as has been, mentioned. I also noticed more water flow after turning the cover plate over. Of course, if the backplate is worn badly, it still may not be enough.

You could also buy a speedseal, if your cover is worn as well. At about $500, a new pump would not be my 1st try.

Before fixing, I was had to close the raw water seacock when sailing, to keep the prime, and then open before starting the engine. This did work, but I didn't like having to do it each time.

When mine did start to overheat, I was often able to "correct" it by closing the seacock for 10 seconds, to build some suction, or quickly pulling off the raw water to exhaust elbow hose, and revving the engine a couple of times.

Best of luck.. Check that cover closely for scoring. I used an RTV silicon (automotive type) instead of paper gasket, and it works well.
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Old 05-25-2009
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thanks for the heads up
based on all this advice our marine mechanic has given us a new pump for trial, if it works we'll buy it, if not, we'll be back here asking for more advice

glad to hear (Northeaster) that there are similar problems out there, and we're not losing our mind!
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Old 05-26-2009
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let us know how you make out!! I would think a new pump should overcome issue stated, such as loss of priming, etc. In my case, turning over the cover provided enough improved efficiency, that it worked fine. However, in a few more years, the back plate may be worn enough to cause similar issues, who knows. I don'y want to spend too much on a 25 year old engine, but it just keeps on going, so what do you do! If ever I am faced with hundereds / thousand $$ repair costs, I will opt to put my money into a new engine.
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Old 06-26-2011
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One other thing you might want to look at is the Mixing Elbow in the exhaust.
I have just spent many hours troubleshooting an overheating problem that ended up being a clogged mixing elbow. I found it after replacing everything else in the cooling system including impeller, hoses, thermostat, temp sensor, etc. The mixing elbow was clogged with rust that moved. sometimes it would totally block the water and other times it would let it pass... Just a thought and a lot cheaper than a new pump.
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Old 06-26-2011
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Two year old thread. Hope he fixed the overheating problem by now.
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