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Old 09-08-2022, 16:17   #1
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An electric pump instead of the Jabsco impeller??

I have just had to completely dismantle all the raw water system on my Perkins 4.236, due to the inlet getting clogged, which caused the Jabsco impeller to run dry, and shred all its vanes into the engine.
I want to replace it with a separate electrical pump, preferably a diaphragm type.
Has anyone done this, and if so, which pump is best?
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Old 09-08-2022, 16:20   #2
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Re: An electric pump instead of the Jabsco impeller??

Quote:
Originally Posted by Jolly Roger View Post
I have just had to completely dismantle all the raw water system on my Perkins 4.236, due to the inlet getting clogged, which caused the Jabsco impeller to run dry, and shred all its vanes into the engine.
I want to replace it with a separate electrical pump, preferably a diaphragm type.
Has anyone done this, and if so, which pump is best?
why not fit a simple raw water flow meter , I made up one from a few parts
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Old 09-08-2022, 16:22   #3
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Re: An electric pump instead of the Jabsco impeller??

Quote:
Originally Posted by Jolly Roger View Post
I have just had to completely dismantle all the raw water system on my Perkins 4.236, due to the inlet getting clogged, which caused the Jabsco impeller to run dry, and shred all its vanes into the engine.
I want to replace it with a separate electrical pump, preferably a diaphragm type.
Has anyone done this, and if so, which pump is best?
I recommend against this. I know it sounds good… better even for a genset that powers the pump and I did just that but found that at high load it overheated and this was caused by the pump because switching back to impeller fixed it. And this was a big March LC3 pump on just a 10hp 3-cylinder diesel of my Northern Lights 6kW genset.

Here’s a tip: route the hose from sea-strainer to pump so that it comes down to the pump before connecting to it. This ensures that the pump is flooded when you kill the motor, lubricating the impeller next start. The impeller will last 2-3x longer this way.
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Old 09-08-2022, 16:50   #4
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Re: An electric pump instead of the Jabsco impeller??

Installing an external pump seems like a good idea, which I have been thinking about, but no experience. I'm curious, how did you size the March pump? It spec is 8.5 gpm, which seems sufficient, but it's only a 1/20 hp motor which seems very small. Most small pumps are very sensitive to flow restrictions.
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Old 09-08-2022, 17:10   #5
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Re: An electric pump instead of the Jabsco impeller??

Two issues:

Most diaphragm pumps will not output enough water to cool that engine.

The engine driven pump automatically adjusts its output based on engine speed. If you have a pump that outputs enough water to cool the engine at maximum load, are you SURE the engine will blow enough exhaust gas to clear that much water through the exhaust system at idle?


Also... The reason most people have trouble with the little mag drive centrifugal pumps moving enough water to cool an engine despite having free-flow specs more than high enough is they are forgetting the significant exhaust back pressure they have to pump against. There are good reasons that these engine are equipped with positive displacement pumps as standard.
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Old 09-08-2022, 17:46   #6
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Re: An electric pump instead of the Jabsco impeller??

Do you have an exterior screen on the engine intake? I know there are many negative aspects to having one (for example, the screen itself can become clogged with growth), but in my experience they help more than harm.
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Old 10-08-2022, 05:54   #7
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Re: An electric pump instead of the Jabsco impeller??

Thanks for these replies:
When you are forced to traverse the ICW to get anywhere with a 6’6” draft, it’s almost inevitable that you hit bottom sometimes. What happened here is that due to an emergency grounding the large main filter became totally blocked with muck, inside and out, I know, I know: the filter should have been inspected but I had other things on my mind. The pump ran dry, and all—I mean all, the vanes broke and tons of muck went first through the oil heat exchanger, then into the engine heat exchanger, then who knows where in the block. I even found a bit in the exhaust water jacket.
The impeller is a crappy little 2” Jabsco, and there is a 24” drop from the main inlet filter to the pump, which is also below the waterline, so it should always be flooded—but not when the filter totally clogs up. It was like I had closed the seacock.
I guess the only remedy is to check the main filter, every time before we leave the berth, (but who does that?) or when we ground, which I expect will be frequently now we’ve moved to the Pamlico, which is quite shallow in places.
I could also fit a second big filter.
The amazing thing is the engine kept running, although we had to reduce revs and watch for overheating.
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Old 10-08-2022, 06:05   #8
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Re: An electric pump instead of the Jabsco impeller??

Quote:
Originally Posted by Jolly Roger View Post
Thanks for these replies:
When you are forced to traverse the ICW to get anywhere with a 6’6” draft, it’s almost inevitable that you hit bottom sometimes. What happened here is that due to an emergency grounding the large main filter became totally blocked with muck, inside and out, I know, I know: the filter should have been inspected but I had other things on my mind. The pump ran dry, and all—I mean all, the vanes broke and tons of muck went first through the oil heat exchanger, then into the engine heat exchanger, then who knows where in the block. I even found a bit in the exhaust water jacket.
The impeller is a crappy little 2” Jabsco, and there is a 24” drop from the main inlet filter to the pump, which is also below the waterline, so it should always be flooded—but not when the filter totally clogs up. It was like I had closed the seacock.
I guess the only remedy is to check the main filter, every time before we leave the berth, (but who does that?) or when we ground, which I expect will be frequently now we’ve moved to the Pamlico, which is quite shallow in places.
I could also fit a second big filter.
The amazing thing is the engine kept running, although we had to reduce revs and watch for overheating.
We don’t check the filter every time we start the engine, but we do check the amount of water coming out the exhaust. With some experience you can easily tell when something is going on
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Old 10-08-2022, 06:22   #9
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Re: An electric pump instead of the Jabsco impeller??

I agree that an external electric fixed-output raw water pump is not an option.

I'm assuming that the OP's engine water temp alarm either was not working, he didn't hear it, or by the time the engine overheated, the impeller was toast.

A flow alarm is a good fix to this problem. Commercial one's are expensive, but goboatingnow might share his DIY design?
The built-in engine temp alarm on the engine control panel is sensing the fresh water temp INSIDE the engine. This temp will take a minute or more to rise hot enough to trigger the alarm, during which time the impeller has already burned up.
To get an almost instant alarm when the raw water flow stops:
Fit a "snap disc" temp switch on the external surface of your wet exhaust elbow just after the water injection point. These snap disc switches come in various temp ranges and are very cheap, around NZ$7. Get a normally open, 70 degree C disc. The disc is about 30mm in diameter. Make a simple mounting band to hold it tight against the wet exhaust elbow and put a bit of heat transfer grease under it. Connect the switch to a loud buzzer (12vt pizzo buzzers cost about NZ$4). Now, when the raw water stops flowing, no water is injected into the exhaust elbow, and within 10-15 seconds the elbow heats up to over 70 degrees (because uncooled hot exhaust is flowing through it), the switch closes and the buzzer says "no raw water shut engine down NOW".
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Old 10-08-2022, 06:33   #10
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Re: An electric pump instead of the Jabsco impeller??

Stick with impeller as engines need consistent flow not pulses.
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Old 10-08-2022, 06:38   #11
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Re: An electric pump instead of the Jabsco impeller??

The problem with many 12v electric pumps is that they are not designed for continuous long term operation. They are designed for intermittent use (think like a washdown pump) and will overheat and fail if run for hours on end. Cheapest solution is to get into the habit of looking regularly at the cooling water flow by glancing over the stern.
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Old 10-08-2022, 09:47   #12
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Re: An electric pump instead of the Jabsco impeller??

Thanks again guys:
My initial question has been answered uniformly. i.e. an electric pump is not a good idea.
I don’t have a temperature alarm, but I do have an engine temperature gauge on the dashboard, from a sender at the back of the head. This is easy to read by the helmsman, and alerted us to the problem in the first instance.
The exhaust flow on my boat is not easy to see when underway, since it is well under the curve of the hull. You have to hang upside down over the transom to see it.
My three-cylinder Kabuto generator is also raw water cooled with a Jabsco impeller, which also flows into the exhaust, so it’s a bit difficult to know what’s what, when both are running.
Goboatingnow’s flow meter sounds like an excellent idea. Perhaps he could show us how to make one?
Also, Nuku34’s idea of a ‘snap switch’ sounds like a good secondary auditory alarm. Would it work on the cylinder head, near the temperature sender, which will rise in temperature quicker than the elbow, if the flow stops? (By the way mate, you may have seen a few of my articles in Boating New Zealand recently, but I’m still learning new stuff, after nearly 50 years of sailing).
Does anyone know where to get one of these in the US?
I will also fit whatever I decide upon on the genny motor.
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Old 10-08-2022, 10:05   #13
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Re: An electric pump instead of the Jabsco impeller??

We lost the raw water pump on our Perkins on the way south in the Exumas. Connected the AC raw water pump to the engine, ran it off the inverter until we got to George Town to where we could order a new pump. The pump had just been "rebuilt" in FL before we left. Bearings had failed.
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Old 10-08-2022, 10:25   #14
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Re: An electric pump instead of the Jabsco impeller??

If you are going to add some kind of an alarm, a water flow switch would be my choice. They are basically a spring loaded paddle, the gets pushed when water is flowing, but the spring snaps it back when the water flow stops. Might be some trouble finding one that will survive well in salt water. Here's an example of one that says brass and stainless steel, but there are probably better choices out there.
https://www.grainger.com/product/DWY...-2-MNPT-55EH46
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Old 10-08-2022, 10:30   #15
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Re: An electric pump instead of the Jabsco impeller??

what if you had an additional Jabsco or Johnson impeller pump, operated by an electric motor, in line?
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