fresh water cooling pump... off the shelf?

Feb 6, 2019
72
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I've been trying to research the specs for an electric fresh water pump system.. GPH, wattage, etc.. turns out, it's pretty scarce stuff.

I was just thinking... in a pinch, could one simply adapt an off the shelf 12v pump for the raw water side?

Such as this?
https://www.harborfreight.com/12-volt-dc-transfer-pump-63324.html

I'm sure there's a very good reason... longevity, noise, service, etc... but what makes a $500 marine impeller pump (which requires an expensive $122.00 service kit) different other than limited production and "boat" tax?
 
Jan 11, 2014
11,323
Sabre 362 113 Fair Haven, NY
Does your boat currently have an electric raw water pump?

Most, if not all, raw water pumps are engine driven. As such the volume of water that is pumped through the cooling system varies based on engine speed. So what you ask? Well, engines are designed to operate most efficiently at a specific temperature, closed systems at around ~160° F and raw water cooled systems at ~130° (each engine will have its own specs).

At slow speeds or at idle the heat generated by the engine is fairly low, so to maintain the proper temperature very little water is needed. If too much water is pumped through the system, the engine will not reach or will take an exceptionally long time to reach the operating temperature. If the engine runs too cold there will be increased condensation in the crankcase, oil will not lubricate as well, and fuel may not be burned as efficiently.

Conversely, when running the engine at a higher RPM and under load, considerably more heat will generated which will require greater water flow to prevent overheating. Over heating the engine is bad, much worse than running it cold.

So, as a permanent solution, the electric pump is not a particularly good idea unless its pumping rate can be varied with engine speed.
 
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Feb 6, 2019
72
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Ah great insights. No - my current engine is FWC with a belt driven pump.. but this is also a bit of thought exploration. Could it be done, would it make sense, what are the challenges?

So what I'm getting is that regulating the raw water flow is an important factor in the design of an electric FWC system.

I made a phone call to the manufacturer of my heat exchanger to ask about water flow (Seakamp Engineering). The first thing they said is that they just can't recommend going with an electric water pump of any configuration. Mostly due to service and parts concerns.

But they didn't seem to be very worried about having to regulate the pump output. That was my impression. I got a recommendation of 7 to 8 GPM for raw water flow. That's 420 - 480 GPH. That's more than I thought it would be!
 
Jan 11, 2014
11,323
Sabre 362 113 Fair Haven, NY
If you have a heat exchanger there are 2 water pumps.

The internal water pump circulates water through the engine block and into to the heat exchanger. This is usually driven by a belt run off the flywheel that also drives the alternator.

The second pump is the raw water pump, it is driven by some mechanical means from the engine. It is like the PTO on a tractor. This pump is external to the engine and has the impeller.

Could you add an electric pump? Sure, is it a good idea? I'm not so certain. If it was a good idea, then there would be a lot of people doing just that.

One last thought, the engine no doubt has a water lift muffler and uses water to cool the exhaust as it enters the hoses. Exhaust pressure lifts the water out of the muffler. When the engine is idling there is very little exhaust pressure and very little water being injected. The exhaust pressure can force the water out. If the external pump pushes more water into the exhaust system than the exhaust can push out, what happens?
 
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Nov 10, 2012
22
S2 9.2 ST IGNAGE, MI
The harbor freight water pump puts out over 100 psi. Way more then the engine should have. And it is very noisy.
 
Feb 6, 2019
72
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Anyone know the PSI on the internal water pump? I read elsewhere that the internal water pump varies between 4 and 8 GPM at the normal RPM range.
 
Nov 6, 2006
9,884
Hunter 34 Mandeville Louisiana
The little harbour freight pump makes 40 feet of head. That is about 17 psi. Rubber impeller pumps generally make a max of around 10 psi reliably. The engine driven raw water pumps make around 4-6 psi to get into the mixing elbow.
 
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Oct 22, 2014
20,993
CAL 35 Cruiser #21 moored EVERETT WA
but what makes a $500 marine impeller pump (which requires an expensive $122.00 service kit) different other than limited production and "boat" tax?
An interesting discussion.
Certainly supply and demand are at play here from an economic perspective. Yes there is the perception that "Marine Parts are always much higher then Land Parts", but there is also the fact that marine parts have been tested in marine environ. They have been modified to provide a level of reliability in this environ. This all has a cost. Each boat owner has free choice to select a marine tested part or a land based part on their boat. Sometimes they are successful other times it fails miserably. You get to be the judge.

The philosophical question aside, with an engine based pump that must work when required and at some point will fail, buying a part that has supporting history and longevity in the harsh marine environ may be good money spent, even if it is significantly more than a "Harbor Freight" product. On the other hand you can approach the problem differently. "I am going with the low cost item and consider it disposable. I am going to change out the item every 6 months because that is how long I think I can trust the item to work. Since it costs so much less I can afford to do that 20 times before the more expensive part would fail." This thinking is used all the time. Only flaw is the aspect of human nature.:yikes:
We get to the point of "I should change the unit out as it is 6 months old" and we see that it is still functions. "It still looks shiny. I'll give it another 6 months." And we are approaching a narrow entrance on a stormy night with waves and rocks to the left and right when suddenly the water pump quits and the engine seizes and we are not wearing our PFD. That is when the $500 seems like a very small amount of money. And we pray to God,:pray: if you get me out of this jam I promise I will always buy marine parts and I will never sin again....

But then I have an imagination...:biggrin:
 
Jan 11, 2014
11,323
Sabre 362 113 Fair Haven, NY
I think it is safe to say that none of us on the forum like spending more money than necessary on the parts and pieces of out boats. With time and experience we all learn where we can cut corners and where we shouldn't. We also learn that WM is not the only source for boating supplies. ;) There's a reason that West Marine is sometimes referred to as Worst Marine.

Items that are mission critical, like engine water pumps, fittings that are below the waterline, things that keep the rig up, and things that keep the boat afloat are usually worth the extra money for marine grade parts. In other areas, the choice is yours.

On another current thread there is mention of a less expensive caulk to substitute for 4200, it has been tested by Practical Sailor and found to be a suitable substitute in many applications. On my own boat, as I work on it, I change out the cheap hardware store hose clamps for expensive Sandvik solid hose clamps on critical hoses, like sanitation hose and hoses that lead to through hull fittings. However, on the fresh water system I use HW store hose clamps because in the worst case scenario, I end up with all the fresh water in bilge and an empty water tank. I learned this when a HW clamp rusted out. Fortunately I found the clamp before the hose came loose and filled the bilge with head outflow. :(

There are ways to sail economically and safely, ask here and research alternative sources. Learn where you can save money and where you should bite the bullet and spend the bucks. Replacing the water pump with a cheap HF pump is not a place to save money.
 
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May 17, 2004
5,031
Beneteau Oceanis 37 Havre de Grace
I noticed in Newbie's original post that he said "in a pinch". Based on that I assume that he means to ask about the pros and cons of using a pump like that as a spare for emergencies. For that use case, the critical metric is less about the durability of the pump, and more about cost, size/weight, and compatibility with the engine. The size and weight are probably not really any better with a HF pump than a spare OEM pump. The compatibility with the engine may or may not be Ok depending on the flow rate and PSI. The cost is obviously much less with the HF pump, but if your main pump fails you will still need to replace it with a new long term solution, probably not just the HF pump. For that reason carrying the HF pump as a spare isn't really a cost savings, it's just deferring the cost of the new OEM pump until you need it instead of paying it ahead of time for a spare. All in all, that doesn't leave any real advantages to the HF pump as a backup unless you really think it's durable and reliable enough for long term use.
 
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Feb 6, 2019
72
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Great thoughts here! I just wanted to add that Harbor Freight is not very relevant. I was in fact walking by the pump section in Harbor Freight when the thought occurred to me. But I wouldn't advise anyone to substitute a critical component unless you're stranded somewhere.

I've actually read about others having substituted the wash down pump in a pinch.

Engines like the A4 can easily be re plumbed as RWC on the fly so the electric raw water pump is less crucial.

Also, it may he easier to use the internal pump for raw water and find a pump for antifreeze instead.

I would be curious about what's available on the automotive side.

There are quite a few electric FWC builds on forums and kits available. But I haven't found much data on the parts they used.
 
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Oct 22, 2014
20,993
CAL 35 Cruiser #21 moored EVERETT WA
I was just thinking... in a pinch, could one simply adapt an off the shelf 12v pump
and
I'm sure there's a very good reason... longevity, noise, service, etc... but what makes a $500 marine impeller pump (which requires an expensive $122.00 service kit) different
@Davidasailor26 I can see how your view "in a pinch" can lead to the conclusion of "it is just a back up in an emergency" idea.

When reading the second part of the post, my thoughts changed. Here is a query about the value of Marine vs Not Marine parts on a boat.

It is a subject that I like the way @dlochner addressed. There are parts of my boat that I can view and temporary and not critical and parts that are critical and I will spend money to minimize risk.