Water Pump Leak

Ammonite said:

If the pump won't prime after a (typically) brisk sail and you don't have a blockage then you either have an airleak (strainer lid, jubilee clips, raw water pump) or the pump is worn and has lost some of its suck. If you fill the pipework manually by topping up the strainer it will probably work (I'm assuming you hadn't drained the pump when on the hard which is why it was working before) but when sailing quickly the venturi effect can pull air into the system and if the pump is worn and/or you have an airleak it will no longer prime. Often this is because the inside of the cover plate has worn in which case you may be able to simply reverse it provided its flat and not stamped with the part number etc. Alternatively you can buy one as part of a refurb kit. A worn seal and/or shaft in the pump can also allow air in or the body of the pump can wear. The former are easy to repair and the latter probably means a new pump. Other reasons for a raw water pump not working include a blocked heat exchanger / exhaust elbow or a failed impeller where the rubber has separated from the central boss but this sounds unlikely in your case.

I hope that helps. I did have a quick look for a YouTube video but you may have better luck if you search the manufacturer. If the cover plate has 3 screws I think its a Jabsco. If it has 6 it should be a Johnson and if you can identify the relevant rebuild kit it's not complicated even without a video.

Click to expand...

NickWilson1972 said:

On the way home thinking about this I realised the impeller is 2-3 inches above the water line. The operators manual is silent on this but is the impeller self priming or does the system need to be filled with water? The most practical way to do this would be to disconnect the hose going to the anti siphon point (highest point in the cooling system and then backfill from there. Kicking myself I didn't try this earlier...

Click to expand...

NickWilson1972 said:

Following previous advice I spent the afternoon looking for air leaks - even went to the extent of using drain trace fluid to try and see if any of the pipes leaking. Tried different gaskets and o rings on the impeller housing. Ran the engine with the impeller cover off. Its turning nicely so that rules out the sheared drive shaft . Confirmed again no blockages from inlet to exhaust - orange drain trace is most helpful.

Still no flow.

On the way home thinking about this I realised the impeller is 2-3 inches above the water line. The operators manual is silent on this but is the impeller self priming or does the system need to be filled with water? The most practical way to do this would be to disconnect the hose going to the anti siphon point (highest point in the cooling system and then backfill from there. Kicking myself I didn't try this earlier...

Click to expand...