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  #11  
Old 06-09-2003
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MD3B Volvo-Penta sea water to fresh water conversion

George, thanks again. I appreciate your patience with my ignorance. I think your answer is in reference to the fresh water cooling pump, as you refer to the thermostat in the system to keep the water temp at 180 degrees. My question is in reference to how large a sea water pump do you think I might need? George, I hope that I don''t confuse the daylights out of you. Let me try to explain this way. In an earlier message you recommended that I use a live well circulation pump to pump the sea water for the heat exchanger rather than go to the trouble of rigging up a belt driven pump like you did. My problem is that I have found a great number of 12 volt live well pumps. They range from a 3.6 gpm diaphram pump to 17 to 25 gpm centrifugal pumps to 5.5 gpm vane pumps to a pump referred to as "Thruhull Bait Pumps that pump 500, 750, and 1100 gpm''s. WOW! suddenly I''m overwhelmed with pump options. What I''m trying to deduce is, what kind and what GPM pump would best be suited to pump the sea water for the heat exchanger. Boy, that was a mouthful, I hope I haven''t lost you. Many thanks, Peter
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MD3B Volvo-Penta sea water to fresh water conversion

Just happened to reread this engine cooling water post and noted that the last part of my post was nonsense. The salt water doesn''t recirculate through the thermostat but goes straight through the heat exchanger and out through the exhaust. Sorry for any confusion, George
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MD3B Volvo-Penta sea water to fresh water conversion

George, what size 12volt sea water pump would I need for the heat exchanger? In a previous message you suggested a live bait pump for this purpose. It turns out live bait pumps range from 3.6 gpm all the way to 1100 gpm and include vane, centrifugal, and diaphram pumps. What do you think would be best for me to try on my first attempt at setting this up? I don''t mind trial and error and then compensating. But, the range is so great I don''t know where to begin. I appreciate your advice. Read my last message. Regards, Peter
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MD3B Volvo-Penta sea water to fresh water conversion

Peter: I don''t know what the HP output for the MD3B is. If it is less than 20 HP I would start with a 3.6 gpm vane pump. For other sizes I would just figure about 1 gpm for each 5 HP, ie., 6 gpm for 30 Horsepower. Regards, George
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Old 06-13-2003
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MD3B Volvo-Penta sea water to fresh water conversion

George, the MD3B is rated at 36 HP, so I''ll look for a pump above 6 GPM. Thanks again for taking the time and putting the effort into disolving my ignorance. Are you getting tired of replying to my questions? This one question has gotten a lot of mileage. To date, 136 hits. So, we must not be too boring to others. Here''s yet another question if you want to take the time. What would be the disadvantage of installing a 750 GPM live well pump? I found several of these and they are far less expensive than the live well pumps that pump 3.6 to 9 GPM? I suppose I could just experiment and see what the results are, but if you know about pumps maybe there is a distinct disadvantage. Regards, Peter
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Old 06-14-2003
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MD3B Volvo-Penta sea water to fresh water conversion

Peter: The only disadvantage of a 750 GPM pump is its physical size and if electric, its power requirements. But if the price is right it will do the job. If I were doing it with such a large pump I would hedge my bet by installing a valved bypass around the pump from the discharge side back to the suction side. The valve in the bypass would allow you to regulate the flow to what works best. Just kidding, but with that kind of flow available, you could plumb in a hose bib and washdown the decks, hose off the anchor or fight fires. Regards, George
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Old 06-14-2003
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MD3B Volvo-Penta sea water to fresh water conversion

Hi pjfsail.

I just completed the conversion of my MD17C. Haven''t used it yet, as I am on the hard. However, I am using the MD17C to replace a MD2B which was also converted.

The pump solution is an easy one. Johson pump makes a "double pocket" pump that will directly replace the exisiting pump on the MD3B. What is is a pump that stacks on top of the water pump that bolts to the engine, effectively giving you two pumps driven from the same shaft. No need to worry about pump sizes or anything, as the pump is designed to the engine.

I''d got mine from http://www.johnsonmarinepumps.com/. Call and talk to a guy named Bill Tibbits. He will be able to supply you with pumps, extra impellers, etc.
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MD3B Volvo-Penta sea water to fresh water conversion

George, thanks again for the input. I never thought about using the pump for different purposes like, deck washdown etc. Read the next entry after yours about a pump company making a dual pump for the MD3B that will bolt right up to my engine. If this doesn''t work out I''m after a deal on a 750 gpm pump. I want to thank you again for all the effort you have put into me and solving my problem. I''ll keep in touch and let you know how I progress. Peter
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MD3B Volvo-Penta sea water to fresh water conversion

Thanks for your input in helping me come to grips on how to go about converting from sea water to fresh water cooling. I will contact the company the first part of next week for particulars. Do you have any idea of the cost of the dual pump? What did you use for a heat exchanger? I''d like to hear more about your experience with the conversions. Thanks again, Peter
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Old 06-15-2003
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MD3B Volvo-Penta sea water to fresh water conversion

The pump was not cheap. I first bought the stacker pump, hoping it would just fit on top of the pump I already had. It didn''t, so I had to buy the main pump also. Total was around $300.

Since I was switching engines, I took the heat exchanger off of the old engine. It was manufactured by San Juan Engineering in Seattle. I had called the company, as the coversion was originally sold as a kit. However, they told me they no longer sell a kit for that engine. That said, they still have the specs and should be able to supply a heat exchanger. They can be reached at (360) 734-1910.

Installation is really straight forward.

Good luck,

Steve
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