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post #1 of 19 Old 06-06-2009 Thread Starter
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Yanmar raw water cooling problem

I have been having problems over the last several weeks with no flow in raw water. But has consistently clears quickly when running. Today it worked great on leaving the marina. After about an hour wind died and had to start it to move off lee shore when wind died. No water, but when I ran it up, water appeared and then ran dark black for a bit and cleared and ran well. I shut it down and after sailing for a few hours, on restarting no water.

The raw water intake is not plugged. I then removed the water pump. Water gets to the pump and the impeller looks in good shape. I am curious about the black flow of water

This is a new boat to me and does not yet have a raw water strainer. The engine is a Yanmar 2gm. The boat is 1976 Northern 29, but was repowered from Atomic to Yanmar, no idea when.


Any thoughs appreciated.

Last edited by noreault; 06-07-2009 at 08:56 AM.
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post #2 of 19 Old 06-07-2009
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Do you have a seacock to close off the intake when the engine is not running?
If not then I'd suggest your making the pump re-prime itself every time you start the motor.
Strongly recommend you fit a strainer, easier to clean gunk from that then having to disassmble the pump.
Also running the pump dry every time when you start will shorten the life of the impeller.

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post #3 of 19 Old 06-07-2009 Thread Starter
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Yes there is a seacock and I close it at the dock but not with the engine off when I am sailing. Why would be be dry? All the lines are below water until the exhaust. The boat is new to me and the strainer has just moved to the top of the priority list.
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post #4 of 19 Old 06-07-2009
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Quote:
Originally Posted by noreault View Post
Yes there is a seacock and I close it at the dock but not with the engine off when I am sailing. Why would be be dry? All the lines are below water until the exhaust. The boat is new to me and the strainer has just moved to the top of the priority list.
Not being able to see your installation it was just a thought.. On my own boat also with a raw water Yanmar I always close the seacock whenever the engine is not running.

Yes, mine will also refill the strainer with the seacock open and the boat level but on the times I have been sailing and not closed the seacock I have sometimes observed the level in the strainer going down.. I'm thinking this may be caused by the boat heeling or even water passing over the open intake and drawing out by some low pressure effect.

Try closing it as soon as you shut down the engine. It's an easy test and if it makes no difference then you can start looking elsewhere.

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post #5 of 19 Old 06-07-2009
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Sounds like the pump is not picking up a prime on restarting. The black water is just some soot that accumulated in the exhaust when no water was flowing. You may need a new impeller or more likely the clearances in the pump have opened up over the years. Sometimes removing the cover and if scored, filing it smooth will solve the problem. I doubt a strainer will help your problem. Note that I only close the seacock of my raw-water cooler Universal diesel at the end of the sailing day, not every time I shut it down. If you have to do that to keep the pump primed, fix the pump.
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post #6 of 19 Old 06-08-2009
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Mine did the same thing. My cover plate (and back plate somewhat) were scored from wear. After turning over the cover plate (clean new surface), my pump worked much better, and no longer lost it's prime - like yours.
I believe that the water rushing past the hull, while sailing, causes (Venturi effect???) which helps to pull the water inside the pump and hoses (along with back pressure from exhaust possibly) You then get air and pump has to reprime.

Have a look at cover for wear, and if so, clean up other side and flip over. I used a very thin layer RTV (auto) silicon gasket instead of the paper gasket. You want it thin so that the impeller is as close as possible to the cover plate.
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post #7 of 19 Old 06-08-2009
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Mine did the same thing. My cover plate (and back plate somewhat) were scored from wear. After turning over the cover plate (clean new surface), my pump worked much better, and no longer lost it's prime - like yours.
This trick only works if you have an unpainted, un-engraved, plain flat cover plate. Many are engraved with part numbers and such.
Quote:
I believe that the water rushing past the hull, while sailing, causes (Venturi effect???) which helps to pull the water inside the pump and hoses (along with back pressure from exhaust possibly) You then get air and pump has to reprime.

Have a look at cover for wear, and if so, clean up other side and flip over. I used a very thin layer RTV (auto) silicon gasket instead of the paper gasket. You want it thin so that the impeller is as close as possible to the cover plate.

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post #8 of 19 Old 06-08-2009
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SD - yes, it would have to be a flat, clean surface, with no engravings. I believe that many of the yanmar 2GM, perhaps 2GM20 pumps do have a smooth surface. I just cleaned mine up with a wire wheel prior to re-installing, so it had a smooth bronze finish.

Ultimately, the back plate may be scored as well, but in my case, just dong the cover was enough to improve the water flow volume, and overcome the same problems encountered by the OP.

Proir to doing this repair, I would have to close the seacock while sailing each time, and thne reopen before staring the engine. If I forgot to close it, it owuld start to overheat, and I would have to either:
1. close seacock for about 10 seconds with engine running, and rev engine, to create some suction, or
2. pull off the water line from exhaust elbow and rev engine a coupleof times, to restore water flow.

Since flipping the cover, I have sailed about a dozen times, and have not had this problem again!

Of course, a new pump would be best, but spending $500 on a new pump for an old engine is spending about 10% of the price of a new engine. I would advise tryining the cover trick, as it may increase the pumps efficiency enough to work for many years.

OP-
Try pulling the hose off of the (closed) engine seacock, and running the engine from a bucket of water. Measure how long it takes to empty the bucket at idle, and also at a higher RPM, when engine is warm.

Then switch the cover plate, and measure the flow rate from the bucket again. In my case I noticed an improvement, and knew that i had at least improved the pump somewhat.

I also replaced the small phillips head scews (in the water pump cover plate), which are easy to strip, with new stainless allen head screws, from a local fastener shop. A bag of 20 screws was about $6, so now I have spares, if any start to strip.
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post #9 of 19 Old 06-08-2009 Thread Starter
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Thanks for all the information. Yesterday afternoon I took the pump off and checked out the cover. I cleaned up the cover with emery paper and put on a new gasket. No chance to reverse. But I think the problem was more lack of cleanup from previous gaskets as opposed to scoring. It is now bright and clean. The pump primed quickly and the flow seem better than before. Well now I will need to test, but it was only an occasional problem.
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post #10 of 19 Old 06-08-2009
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Sounds like you are on the right track. A buildup of old gasket material would keep the cover from being tight against the impeller. Was there much visible scoring on the inside of the cover plate?
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