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Old 06-03-2013
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Yanmar 2GM20F - Not pumping water at slow speeds

I am looking to get ideas on possible issues with my engine cooling systems.

Symptoms:
Occasionally no water flow at idle at the dock. (increase in RPMs allows flow)
No flow when idleing in reverse backing into her slip.
When not pumping the exhaust girgles
Water flow when flowing is as it always has.

I have checked:
Seacock is open.
Strainer is clear.
I disconnected the hose at the pump intake and... there is no flow restriction.
I have opened the pump and checked the impeller and pump casing, impeller was good and there was no scoring on casing.

Any thoughts would be greatly appreciated.

Thank you.
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Old 06-03-2013
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Re: Yanmar 2GM20F - Not pumping water at slow speeds

Sucking air? Could have a small leak between the seacock water pump output.
I'd take a close look at, if not just replace, the gaskets.
When was the last time you replaced the impeller? And was it the correct one?
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Re: Yanmar 2GM20F - Not pumping water at slow speeds

Captainmeme, I do not think it is sucking air since the pump intake is lower then the waterline it does not leak out when not running so I would assume it does not leak air in when in operation.

The impeller was replaced the end of last season. It was an original OEM impleller for the engine.

The part of the system that does not make sense to me is on the back side of the exhaust, could it be something associted with the heat exchanger itself, mixing elbow or the muffler?
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Re: Yanmar 2GM20F - Not pumping water at slow speeds

Could be old impeller bits in the front of the H/E bundle, or indeed carbon buildup at the elbow.. both are good candidates for obstruction to water flow. Is temperature an issue yet?? No exhaust system leaks below??
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Re: Yanmar 2GM20F - Not pumping water at slow speeds

I will take the a look into the end of the heat exchanger to see if there is any obstructions.

Is it possible to clean the elbow or is it a part that you just replace. If you clean it how would you recommend cleaning it?

Temperature has not been an issue that I know of. There is not gauge only the audible alarm and buzzer on the Yanmar panel. I do not believe there are any exhaust leaks there is no water not diesel exhaust smells below deck.
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Re: Yanmar 2GM20F - Not pumping water at slow speeds

Same problems here and working on it
You can clean the elbow I removedthe 4 bolts on the engine and disconnected the entire thing ( elbow and connector)
Let it soak in a bucket filled with phosphatic acid. (Home Depot ) for a couple of days, Dilutes and removes most of the carbon and rust Less agressive than muriatic acid Rince a few times and stop the action of acid by soaking againg in fresh water and baking powder

Worked fine for me but did not really solved my water flow problem
Need now to do the same with Heat exchanger

Good luck
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Re: Yanmar 2GM20F - Not pumping water at slow speeds

I assume you have checked the belt condition and tension. Belt could be slipping at low rpm.
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Re: Yanmar 2GM20F - Not pumping water at slow speeds

I will remove the elbow and try the phosphatic acid clean. I will take a look at the heat exchanger.

I have checked belt tension and does not seem to slip.
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Re: Yanmar 2GM20F - Not pumping water at slow speeds

Is this somthing that just started? has it in the past pumped water at idle? Does engine over heat when idling?

My engine will also not seem to pump water at idle. But what is happening is the water lift muffler is filling with water, then the exhaust will blow a big slug of water out and clear the water lift muffler, then no water for 30 seconds or so, then another slug of water. At idle the pump on my 3gmd is probably only puming 1/2 gpm, and this water is only seen coming out of the exhaust as a slug of water. I hook a bucket up to flush my 3gmd after each use so I can see the flow rate.
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Re: Yanmar 2GM20F - Not pumping water at slow speeds

Do you have a intake screen on the hull of the boat covering the through hull?

I have a screen and I need to keep it clean, or it would slow down the flow.

I would replace impeller with a genuine yanmar as wear on the sides will reduce flow rates. The rubber impeller may also be spinning on its metal inner part.

Running the engine in reverse should have no effect on water flow. Engine rpm is the only thing that should effect water flow.

Last edited by casey1999; 06-03-2013 at 05:00 PM.
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