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Yanmar /Kubota Water Pump Replacemnt

May 27, 2004
Hunter 30_74-83 Ponce Inlet FL
About six months ago I noticed water not emanating from the exhaust thru hull for my 2GM20F Yanmar engine. So I took the raw water pump to the local yard and found the shaft turning but the impeller sitting idle. I had a new impeller installed then and afterwards,as usual, started the engine and ran it for 20 minutes once a month to keep every thing moving.
On June 13 I went on cruise for a week to St Augustine with the engine being used 6 hours a day with no problems. But yesterday when I started the engine again, no water came out.
The thru hull is and has been clear of obstructions. Volume of water when running normally is quite normal. The hose is less than a year old. The mech thought it had been run "dry" (how I don't know).

So, Any thoughts on the problem?

Secondly, is there a Kubota or other brand of raw water pump available to me so that I don't spend an entire SSI check at the Yanmar dealer?

Thanks in advance.
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Nov 6, 2006
Hunter 34 Mandeville Louisiana
Impeller can be destroyed by partial water obstructions on the intake side (strainer, thru hull, hose collapse) or on the discharge side.. (plugged fitting on mixing elbow, trash plugging heat exchanger inlet, kinked hose) Either way, it would look like "run dry" (to a person not skilled in failure analysis of this type pump).. there were reports of some Yanmar impellers not having a good bond to the shaft fitting, resulting in shaft turning but impeller not turning. Sounds like all you need is a new impeller.. $20-30.. to make the pump run.. but maybe a bit of detective work to find a possible restriction..
Jul 7, 2004
Hunter 30T Cheney, KS
Are you sure it's the pump and not a blockage in the engine? Bits of an old impellor could have found their way downstream. FWIW, My boat has a SpeedSeal cover on the pump to make changing the impellor easier.
I might suggest putting the discharge hose end of the pump in a bucket to see if it is pumping or not.
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Oct 26, 2008
Catalina 320 Barnegat, NJ
Check to make sure your hose doesn't collapse while running. If you don't have a reinforced intake hose, it can look almost normal when the engine isn't running, but clearly be collapsed when the pump is attempting to suck water. The mechanic may see that the hose appears to have been collapsed, which would happen if the pump is sucking against a dry hose for whatever reason. It happened to me because I initially installed an un-reinforced intake hose. All was fine for about a year until my strainer was clogged with seaweed and the discharge was clearly reduced. I didn't have a problem with the impeller after clearing the strainer, but the hose was permanently damaged and had to be replaced (with the correct reinforced hose, BTW).
Jan 17, 2013
Catalina 310 St. Simons Island, GA
I have the same engine and First Mate Yacht Service in St. Augustine is extremely knowledgeable about it. Bo at First Mate also has this engine and is a wealth of knowledge. There are two different water pumps: Japanese and European and the impellers are not interchangeable. I had a Japanese water pump and kept a spare impeller on board and also a spare water pump which was European. Reason is that the European water pump is about half the price of a Japanese pump. My pump started leaking recently and the mechanic advised to replace so I installed the European pump, removed the Japanese pump and purchased a new European pump and impeller as back-ups. Much simpler to stay with one type of pump.


Aug 12, 2014
Hunter 31 (1983) Pompano Beach FL
I had mine fail last year while out sailing with a group of friends. I knew the PO had a spare in the parts box onboard, so I swapped the pump while at sea, and was able to get back to our dock. The spare which looked good when I saw it in the parts box had a decent leak, and a bent pulley which went undetected on my visual inspection of spares. There was also a spare impellor. I ordered two new impellors and gaskets, and refurbed both pumps straitening the bent pulley while I was at it. I tested both pumps, and now I know I have a known good spare in the box along with a new spare impellor.
May 27, 2004
Hunter 30_74-83 Ponce Inlet FL
Justin, I'll try your suggestion to confirm no pump action. If true, I can't just keep replacing impellers.
Scott, I'll check hose next for collapse.
Kloudie, new elbow, and connections including manifold. Bottom done and new thru hull just before cruise.
Cat, I met Bo and his team when there in June on an electrical issue which he solved rather quickly... Great guy and great group of folks. Of course the pump was working then.

I'll report back when I try steps 1 and 2.


Jan 20, 2005
Nauticat 321 pilothouse 32 Erie PA
there is also a very strange failure mode for the raw water intake HOSE to the pump. those hoses are double wall reinforced. when they get old, the interior can collapse on itself when the engine runs at high rpm . high rpm, high raw water demand, interior hose buckles and shuts off flow, engine s tarts running hot, interior hose collapses, boat owner shut it down or backs off to 900 rpm. tries to resume normal operation, same thing happens. everyone with raw water hoses older than 10 years: do yourself a favor and replace it.