Engine Seawater Priming

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Scott Rosenthal

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Aug 28, 2025, 5:02:46 PMAug 28
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Hi,

I’ve been having problems getting my engine seawater pump to prime after air has gotten into the seawater intake hose (e.g., lifting the boat out of the water, opening the strainer to clean it, etc.). Before I spend $1K(!!!) on a new seawater pump, has anyone else seen a problem like this? FYI:

·         I’ve tried new impellers,

·         There are no obvious air leaks (just put in new hoses, just in case),

·         There are no obvious water leaks on the way into the pump.

·         The engine is the Westerbeke 40.

·         I rebuilt the seawater pump three years ago trying to fix this problem, but no luck.

Regards,

Scott
1980 B40 Willow, #110

 

 

Scott Rosenthal
sc...@sltf.com

 

B Hall

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Aug 28, 2025, 5:08:39 PMAug 28
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Check inlet and outlet hosing for any very small air leaks.  After I resealed all my inlet hoses my pump started pumping.  

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Dan Stadtlander

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Aug 28, 2025, 5:40:06 PMAug 28
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Scott,
I’m guessing you have a Sherwood pump. One other thing to check is the cover plate. If it’s worn and not perfectly flat then the impeller won’t seal against it. If it is worn you could flatten it by sanding on a flat plate. 
Dan
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On Aug 28, 2025, at 5:08 PM, B Hall <bhall...@gmail.com> wrote:



Henning Christensen

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Aug 28, 2025, 5:50:13 PMAug 28
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Hi Scott,

Try to let the pump suck from a bucket. If it suck the pump is ok. Then you can lover the sea water hose down under the waterline to ensure there is a free flow before your filter.  Also use wet vac suck water to the pump. Check the connection to the exhaust hose connection can also be done blowing air into the water hose after the pump, then you find out if the heat exchanger is clear.
Good luck.

Henning
B40 , KUTA 1980 # 98 (soon for sale )


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maurice...@gmail.com

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Aug 28, 2025, 8:22:02 PMAug 28
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Scott, this is from memory, but I think my raw water pump is the Sherwood G 65.  Just for kicks about 15 years ago, tried Jabsco impellers…none of them worked.  When I went back to the Sherwood Impellers, maybe 9959, it worked immediately.  Threw the Jabscos out.

Maurice

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On Aug 28, 2025, at 5:02 PM, Scott Rosenthal <sc...@sltf.com> wrote:


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Scott Rosenthal

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Aug 29, 2025, 8:06:08 AMAug 29
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Many thanks to everyone. All interesting comments. I could have been clearer in the problem:

·         Once primed, the pump works well. It’s just the priming that’s the issue.

·         Yes, it’s the Sherwood G65 pump.

·         Both the Sherwood and Globe impellers exhibit the same priming issue. Never tried a Jabsco.

·         I’ve replaced all the intake hoses from the seacock to the strainer to the pump, with no improvement.

·         I have a Speedseal cover on the pump. When I rebuilt the pump in 2022, I did sand down the Speedseal cover using plate glass as a backing for the sandpaper. However, since the Speedseal cover uses an O-ring for a seal, I wonder if sanding it flat actually worsened the problem, since the O-ring will only compress a certain amount?

I still have the original cover and, I think, a spare Speedseal cover. That’ll be an interesting experiment to see if changing the cover fixes anything.

My other thought is maybe to mount the G65 upside down, so that the intake is at the bottom and the output is at the top (why fight air trying to rise like in the current arrangement).

Anyway, once primed, things work well.

Regards,

Scott
1980 B40 Willow, #110

From: bristo...@googlegroups.com [mailto:bristo...@googlegroups.com] On Behalf Of maurice...@gmail.com
Sent: Thursday, August 28, 2025 8:22 PM
To: bristo...@googlegroups.com
Subject: Re: [Bristol39-40] Engine Seawater Priming

 

Scott, this is from memory, but I think my raw water pump is the Sherwood G 65.  Just for kicks about 15 years ago, tried Jabsco impellers…none of them worked.  When I went back to the Sherwood Impellers, maybe 9959, it worked immediately.  Threw the Jabscos out.

 

Maurice

Sent from my iPad



On Aug 28, 2025, at 5:02 PM, Scott Rosenthal <sc...@sltf.com> wrote:



Hi,

I’ve been having problems getting my engine seawater pump to prime after air has gotten into the seawater intake hose (e.g., lifting the boat out of the water, opening the strainer to clean it, etc.). Before I spend $1K(!!!) on a new seawater pump, has anyone else seen a problem like this? FYI:

1.       I’ve tried new impellers,

2.       There are no obvious air leaks (just put in new hoses, just in case),

3.       There are no obvious water leaks on the way into the pump.

4.       The engine is the Westerbeke 40.

5.       I rebuilt the seawater pump three years ago trying to fix this problem, but no luck.

Regards,

Scott
1980 B40 Willow, #110

 

 

Scott Rosenthal
sc...@sltf.com


 

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David Lloyd

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Aug 29, 2025, 5:35:52 PMAug 29
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I have same westerbeke and the o ring plate did not work when I replaced seals and bearings on sea water pump so I hade to use old one with paper gasket.

On Fri, Aug 29, 2025, 4:25 PM David Lloyd <lloydsqua...@gmail.com> wrote:
Try taking off hose after sea water pump and give it a start and see if it primes. Not long so we don't over heat engine.
 That way we know if it's the pump not priming or a issue  like a clog after the pump. Should self prime. 
 Does the pump leak when running?
 
 

David Lloyd

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Aug 29, 2025, 5:35:52 PMAug 29
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Try taking off hose after sea water pump and give it a start and see if it primes. Not long so we don't over heat engine.
 That way we know if it's the pump not priming or a issue  like a clog after the pump. Should self prime. 
 Does the pump leak when running?
 
 

On Fri, Aug 29, 2025, 8:06 AM Scott Rosenthal <sc...@sltf.com> wrote:

Scott Rosenthal

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Aug 30, 2025, 7:32:03 AMAug 30
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Thanks for the ideas. The pump doesn’t leak and there are no clogs after the pump since, once primed, it works great. Interesting that your O-ring plate didn’t work…

Henning Christensen

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Sep 2, 2025, 6:46:41 PM (13 days ago) Sep 2
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How offer and how do you prime it, also is your raw water filter placed higher than the pump? then it could be the seal on the raw water filter.
It could also be a slightly worn shaft seal that allowing air to come in when the pump isn't running. As soon as the pump has been primed and is running its internal pressure makes the shaft seal working properly.

Scott Rosenthal

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Sep 2, 2025, 8:34:13 PM (13 days ago) Sep 2
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I appreciate your thinking about this. The pump works well once I establish prime. Leaving the boat for weeks doesn’t cause it to lose prime. The strainer is in the bilge, lower than the engine. The only time I lose prime is if air gets into the seawater intake line (e.g., opening the strainer to clean the basket, lifting the boat out of the water, changing the impeller, etc.).

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