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Old 05-02-2009, 02:43   #1
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Raw Water System & Impeller

Hi all,

The raw water circuit suddenly stopped pumping the other day - lucky I was still in the marina!!

Motor is a fresh water cooled Sole Mini 34 around 23 years old and is running fine. I had been away for a couple of weeks and started the motor the other day to giver her a run. After about 30 sec I noticed a change in the engine noise & checked the exhaust - no water...

Double checking the seacock was open (yes) and if there was anything else obviously wrong, I took the impeller out. It looked OK - no craking or any other physical damage. I noticed the face plate for the pump was badly scored (both sides - it's 23 years young!!) and put a new impeller in anyway. Started motor again & still no water.

When I bought the boat a coulple of years ago from Sydney I got a mechanic to service the motor & replace the impeller & put some spares on board for the trip to Hobart. The spare impeller was about 3mm less in depth than the orignial after comparing, so I guess this would stop the water pumping along with the scored plate.

I ordered a new plate & genuine Sole impeller & gaskets (Johnson & Jabsco do not make one the same size (depth..)) & will fit on the weekend. While at the boat today I also checked that the sea cock was not blocked and nothing stuck in the hose, Pump body & fittings & heat exchanger - all clear.

Question - when I put it all back together, how long should it take to get the raw water pumping through the system as I don't want to kill the new $55 impeller. The water pump is about at water line level so it doesn't have to lift the water very far. I will lubricate the impeller with gylcerine.

I also turned the motor over to ensure the shaft in the pump was turning (yes).

If it still does't pump - is there anything else I should check before I call the mechanic?


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Old 05-02-2009, 04:27   #2
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You didn't mention checking the sea water strainer, do you have one fitted? Check for a blockage in the thru hull (marine growth / plastic bag) or for a delaminated or collapsed hose on the inlet side. Delamination is not readily apparent. The inner layers delaminate and the suction of the RWP collapses the inner layers while the outside layers look OK.

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Old 05-02-2009, 05:47   #3
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Your HX or wet exhaust elbow could also be plugged! Another possible source is the inner wall of your intake hose could be collapsing under suction..
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Old 05-02-2009, 07:27   #4
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If the engine or strainer is well above the waterline you may have a lot of air in the intake line. The exhaust pressure can sometimes overpower the suction capabilities of the pump. (Especially an old pump) Simply remove the raw water hose at the injection point of the exhaust mixing elbow and start the engine untill you see raw water come out. ( Just 10 - 30 seconds of running time should do it). If you do not get water the issue is elsewhere. Try it. It only takes a few seconds. Let us know what the fix is!
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Old 05-02-2009, 18:51   #5
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Thanks for the suggestions so far. I'm tending to think the intake hose inner wall collapsing may be the problem as there was no sign of any weed/plastic being stuck or sucked in through the skin fitting. The old hose seemed very stiff & badly discoloured so must be pretty old.

I removed the strainer at my last slipping with the intention of fitting a new one, as it was a funny sort of arrangement in that it sat ontop of the sea cock with two outlets - one to the galley & the other to the motor - and a screw lid to get access to the strainer. Problem was that I could not remove withdraw the strainer from the tube like housing as there was not enough clearance due to the hot water cylinder sitting directly above it!! It also placed alot of leverage on the skin fitting - so much so that the fitting was not tight onto the hull and had to be re-done. Other than that, the custom made strainer was a work of art and sure it worked very well before things were added to the boat (hot water!!)..

I have bought new hose & strainer that I will put in an easily accessable location and fit on the weekend - will see how it goes (fingers crossed!!)
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Old 05-02-2009, 19:01   #6
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Another possibility is you are sucking air in somewhere. Most likely a hose fitting.

As for the strainer. You need to be able to access and clean that out often especially in harbors and marinas.
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Old 06-02-2009, 22:45   #7
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Well after a few hours of hot sweaty work I'm now sitting back having a nice cold beer feeling very happy that it's all fixed & working again.

Still don't know what the problem was - but the raw water output now has a very healthy flow. I ended up with new hoses, new strainer, new impeller and new face plate for the pump. The new strainer, while not in an ideal position close the the intake, is in an easy to get to location with good visabilty.

Also replaced a couple of hoses on the motor.

I'll see how it goes for the rest of our summer.

Thanks again for all the suggestions.
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Old 06-02-2009, 23:16   #8
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SUMMER? Then I saw the source of the post.........psssst wanna send a couple days up here? Thanks in advance
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Old 07-02-2009, 00:08   #9
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Originally Posted by Chief Engineer View Post
SUMMER? Then I saw the source of the post.........psssst wanna send a couple days up here? Thanks in advance
Pretty hot in SE Australia today - Melbourne had its hottest day on record about 47 degrees Celcius, Sydney & Canberra were around 40!!

Pretty mild where I am in Tasmania at 25 degrees C.

We have got the wooden boat festival on in Hobart at the moment with 100's of boats on display from huon pine dinghies up to square riggers - hope to get across on Sundy to check them out.

So I will be unable to take you up on your kind offer to visit!!
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Old 07-02-2009, 04:27   #10
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Sounds like a comprehensive overhaul! You may have fixed 4 or 5 other serious issues just waiting to happen as well as fix what the obvious problem without really knowing why.

It usually does not work that way. You most always fix something that may not have been right but was not the problem. The repeated cycle happens until you run out of money, time or actually fix it.


Warmer weather coming both our ways this weekend. Mid 60's and over 70 on Sunday and the rest of the week 60's and mid 50's. It's not summer but it will be welcome.

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