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maintenance of Yanmar water pump impeller


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Lots of experience with these. Short answer is annual replacement but more importantly make sure whole system is free-glowing with no restrictions or partial blockages upstream of pump (eg inlet strainer becoming clogged) or downstream of pump (eg. calcified exhaust elbow). Couple of Qs: What year and size is your engine? Raw water or fresh water cooled?

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The older, smaller models use small impellers that can’t cope with any sort of water restriction (creates an excessive vacuum or bac-pressure at pump) which causes smaller impellers to fail very quickly. I was going through them every 10hrs until I diagnosed problems with restricted water flow. New, bigger units use larger impellors more robust.

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Its a 2GM20 .. in a Farr 940 (N30) be from the mid 1980's  ... boat is kept on a trailer, usually used in fresh water, but gets an annual run in the sea for 2-4 weeks. Its raw water.

 

There is an inline filter (sea chest) so I can see if there is anything 'large' in the system. Water flow appears to not have changed over the 4 years I've had it, but just feel it should get some attention, while I do the fuel and engine oil/filters.

 

Any recommended supplier .... 

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if you intend keeping a yanmar engined boat for a few years, four years worth of filters and impellers from the likes of these guys

http://bayshoremarineengines.com/yanmar.aspx

is similar to the cost of one year's worth considering the extortionate prices charged here, even after postage (youshop or similar) is included

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There are two types of Johnston pumps for these, we just changed ours and went through this rigmarole. One large, one small. Don't change pumps. The thermostat is designed to run with the smaller water flow from the small pump (which we have) and going to the larger one will over cool the engine creating excessive wear. Our impeller was 5 years old, still going but had worn on the face plate of the pump so was losing its effectiveness. New impeller now and face plate machined flat again as it had indentations in it obviously from years of running but do check that plate and use a gasket when reassembling. Incidentally, we had to make our own when the jabsco gasket had the bloody holes in the wrong spot!

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