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Old 13-12-2019, 15:54   #16
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Re: Loss of raw water pump prime

Greasing the inside of the housing will give the pump more suction on startup. I do it every time I inspect an impeller. It keeps the vane ends from getting hard because of friction heat when the pump is dry. In the old diesel manuals.

I think it's air coming in from the strainer or another leaking fitting. A rubber impeller pump will always pump something. Since it's easier to pump air, any leak destroys the suction.
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Old 13-12-2019, 19:16   #17
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Re: Loss of raw water pump prime

If the pump has any age - replace it. I lost prime on the move this summer and visual inspection didn't really show any severe wear. However, it is most likely wear behind the impeller, the cam plate or the cover plate.
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Old 13-12-2019, 23:33   #18
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Re: Loss of raw water pump prime

I thought I'd read other threads commenting about the lifespan of the ubiquitous
JABSCO raw water pumps. I had my two Yanmar 3YM30s overhauled a few years ago. The workshop told me they needed to order a new water pump">raw water pump from Yanmar because one was beyond repair. It wasn't cheap so I didn't replace the other one. I had to admit I'd had regular problems priming after haul-out so I didn't question his decision. Sure enough, a couple of years later the other pump was giving problems - slow to prime on start-up and then low pump output. When I inspected the pump body, it was obvious that the bronze chamber circumference was badly worn, even without any precise measurement. I replaced the pump and everything was fine.

It seems to me these bronze pump bodies are good for 10 years, not more. Perversely, it almost seems that the impeller lasts longer than the pump body.

I wonder if this is your problem?
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Old 14-12-2019, 01:52   #19
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Re: Loss of raw water pump prime

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Originally Posted by sanibel sailor View Post
I have a problem with losing the prime on my cooling system raw water pump. In the past, it loses its prime when I haul out. No big deal. Lost once before after sitting for a long time. Should be part of my "back into service" plan.

However, recently, when out sailing in stronger winds and chop, it lost its prime. This is more concerning as that is exactly when I might need engine assistance most.

Engine is Westerbeke W30, AKA 4-91. Recently went from 3/4" to 1" seacock, added watermaker which tees off with its own valve which remains closed. It was doing it prior to adding the watermaker. Seacock is near centerline and deep underwater. 3/4" wire reinforced hose to strainer which is below waterline, then 3/4" hose to pump, which is also below the waterline. There are no leaks or drips in the system, so I cannot identify anywhere air might be entering. The entire system is below the waterline, no siphon break or anything.

When I have started engine and notice no cooling water in exhaust, I open strainer and get water pouring out immediately which does not restore prime. In order to get it working again, I have to pull the outflow hose off the pump which fixes it immediately, but is a bit of an inconvenience.

I am thinking the water is somehow draining from the hose to the strainer, then the pump loses its prime and cannot reprime. Impeller was good when checked a few months ago.

I will recheck the impeller, but am thinking about adding a check valve in the system. A bit worried about adding a restriction as when I switched from 3/4" seacock to 1", it fixed an overheating problem I had a prolonged higher RPM's.

Any input?
Likely a small air leak in the seal on the impeller shaft I had that on a Johnston raw water pump. They cost buttons to replace once u get the old one out, I would also replace the bearings at same time , and give the pump front plate a polish flat on say a piece of glass plate with a fine wet and dry paper especially if scored .
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Old 14-12-2019, 08:33   #20
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Re: Loss of raw water pump prime

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A temporary work around is to shut off the cooling water seacock, and fill up the water pump, the tubing and strainer with fresh or sea water (by undoing e.g. the cap of the strainer if that is high enough and then re-sealing it). Now start the engine. As soon as the engine starts, open the sea cock.
This priming procedure might be required if the strainer is above water, but mine is below. I pull the lid from the strainer and it gushes water. By the way, I have replaced the strainer lid gasket in the last couple of years.

That also makes an air leak unlikely. The positive water pressure ought to overcome any minor air leak. If present, it would have to be tiny as there are no leaks and I ought to see at least weeping if not a drip.

Thanks for all the input. It has really helped me think thru this problem. The pump has to be the culprit. I will recheck impeller and faceplate. Shaft seal has been replaced. I wonder if the gasket is bad? I have more impellers than gaskets, so I cut some new ones. I matched gasket thickness to stock, and it pumps water fine and doesn’t leak but it might not take much extra thickness to prevent the pump from pumping air when needed, particularly if the impeller is old.
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Old 15-12-2019, 17:44   #21
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Re: Loss of raw water pump prime

I'm telling you that you have a piece of shell blocking the intake just before the seacock! I will bet on it.
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Old 15-12-2019, 19:03   #22
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Re: Loss of raw water pump prime

No strainer over seacock inlet, seacock and associated fittings brand new in Aug 2019. New bottom paint, including inside thruhull. No hard fouling. Works fine most all the time. Doubt it is a shell or barnacle.
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Old 15-12-2019, 19:28   #23
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Re: Loss of raw water pump prime

[QUOTE=chris in SG;3035701]I thought I'd read other threads commenting about the lifespan of the ubiquitous JABSCO raw water pumps./QUOTE]

Quoting myself, I should have said "the ubiquitous Johnson raw water pumps". However, if you have gaskets rather 'o' rings it may be a different pump type and my experience may not be so relevant. But I still suggest you check for pump chamber wear, not just impeller and faceplate.
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Old 20-01-2020, 10:36   #24
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Re: Loss of raw water pump prime

Happened again yesterday. Gave me an incentive to do something. Changed out the impeller. Cover plate was pretty worn. I replaced it with an extra I had. Hauling out today for a short haul. We’ll see how it goes after.
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Old 20-01-2020, 10:45   #25
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Re: Loss of raw water pump prime

Good luck with it, John. Somewhere somehow either air is getting in or a lot of water is flowing back the wrong way. Damned frustrating. Pulling out will give you a chance to look at the system from below. You might consider, while you have it out, backflushing from the pump inlet to the open seacock. That would eliminate some of the possibilities posed by forum members who are trying to figure it out. For that matter, maybe flush forward, too, and prove that it's not a blockage farther along in your cooling system..
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Old 20-01-2020, 13:56   #26
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Re: Loss of raw water pump prime

Seems to be fixed...

No flush test needed. Water flows freely from intake hose into pump and once pump is primed, it works correctly. As the system is underwater and pressurized, any leak should be water out not air in. The impeller pump should handle a small air leak and reprime. I am hoping it was the cover. I have ordered another couple of pieces of brass to make two more covers.
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