# MD3B Volvo-Penta sea water to fresh water conversion



## slosharron (May 10, 2003)

I have an MD3B Volvo-Penta diesel engine cooled with Sea water. I want to convert it to Fresh water cooling. Sen Dure Company sells a kit for the conversion. The sales rep tells me I should not experience any problems after converting. But others caution that years of salt build up may plug up the water jackets. Any one out there have first hand experience with this kind of conversion? Thanks for your input.


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## RichH (Jul 10, 2000)

The salts inside your engine wont migrate to the cooling passages in the heat exchanger .... but they should be cleaned out!

For the ''salts'' (precipitated carbonates) that are inside your engine, simply get a commercial ''descaler'': Marsolve or RydLyme (available through most marine supply houses such as West Marine or Boat/US,
etc.) and recirculate (pump) this into a drained engine, let sit a few hours, flush (into a barrel, etc.) .... that''s it. Both of these products will dissolve the accumulated scale without dissolving the base metal of the engine. Some folks use muriatic or other acids which can dissolve the base metal as well as the scale - therefore harmful. 

BTW - when you change to fresh water cooling, dont forget to change the thermostat to one that open at approx. 190 - 195 degrees. The higher operating temperature will be better for combustion efficiency, etc. 

hope this helps ;-)


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## geohan (Mar 8, 2000)

We converted our Universal Yacht Twin, (the 2 cylinder, 12 HP little brother of the Atomic Four) to freshwater cooling with great success, after 12 years of saltwater cooling. Our heat exchanger was home built out of 2 sixteen foot lengths of 3/8 inch copper tubing which were soldered together along their lengths. This was easy to do as the two coils of bright copper tubing were placed side by side as they came out of their boxes. The soldered coils, one on top of the other were then formed into a flat spiral and attached to the underside of the cockpit sole. (Foot warmer for cold Puget Sound winter sailing) The last foot on each end wasn''t soldered so as to allow for the necessary divergence for the hose connections. The necessary expansion/fill tank was fashioned from 12 inches of 3 inch copper drain pipe although it could have been made from heat tolerant PVC pipe. The hoses were hooked up so that the saltwater and the freshwater flowed through the heat exchanger in opposite diredtions. Lastly, a thermostat was added to allow the engine to get up to a desired 180 degees fahrenheit. This system proved quite satisfactory and maintenance free. Good Luck, George


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## pjfsail (Mar 15, 2003)

George, I really appreciate your reply. Sorry it has taken me so long to ask this question but how did you organize a sea water pump? And how did you make the expansion tank? Did you have a radiater shop make it for you. I wonder if anyone else had made a similar set up. I''d like more information and then give it a try myself. Thanks, Peter


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## pjfsail (Mar 15, 2003)

Rich, this makes good sense to me, thanks for your reply. Peter


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## geohan (Mar 8, 2000)

Peter, for the saltwater pump I replaced the single belt alternator drive pulley with a double sheave pulley to also drive the saltwater pump. This was the hard way since it also required the fabrication of a husky adjustable mounting bracket. The easy way would be to buy a 12-volt bait well pump. The expansion tank was made up out of 3" copper drain pipe and was about a foot long with an inlet at the top and an outlet at the bottom. Since I used a standard car radiator cap, a vent was necessary which lead up and into the rear of the cockpit. If it started to pass steam I would know something needed attention. I see no reason the expansion tank could not be made of the hot water type PVC pipe. Browse through the plumbing aisle at Home Depot and you should be able to find suitable fittings that are simply solvent welded together. Be sure to mount the expansion tank in the high part of the system to avoid air locks. None of this is high tech so don''t be intimidated. Good Luck, George


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## pjfsail (Mar 15, 2003)

George, thanks so much for taking the time to give me the instructions. I am determined to duplicate what you have done. Using a 12v pump makes sense and I''ll look for one. I am still a bit stumped by the expansion tank. I hope you will bear with me for more understanding. If I use PVC (which makes sense) how will I provide for a pressure relief? This is one of the functions of a radiator cap which releases pressure at a predetermined point. If the system isn''t pressurized and a pressure relief incorporated wouldn''t problems exist? When you made yours out of copper 3" x 12" pipe did you have a radiater cap neck soldered to the pipe so you could use a cap to pressurize the system?
Thanks again for allowing me to pick your brain. Peter


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## geohan (Mar 8, 2000)

Peter I didn''t pressurize the freshwater cooling system as it isn''t necessary for a thermostat set at 180 degrees F. Only if you intend to operate above 212 degrees F like most new cars, do you need pressurization of the cooling water system. Install a small pipe near the top of the expansion tank as a vent to prevent pressurization. My copper tank was brazed together with a vent of 1/4 inch tubing led up to the cockpit so I could monitor it in case of over heating such as might occur if one of the neopreme vanes in the pump shears off and partially plugs the plumbing at the first bend downstream. (In an emergency the pump will function quite well enough missing one or even two vanes if the missing vanes are recovered). You are welcome to the "pickings" slim as they might be but hopefully gudenuph. George


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## pjfsail (Mar 15, 2003)

George, thanks again. I think the pickings are more than slim, maybe you need to give yourself a little more credit. You''ve got a big pat on the back from me. In any event, all of what you say makes a lot of logical sense to me. I never gave a thought to the fact that automobiles run at the boiling point and that is the reason for pressurizing the cooling system. I''m going to go ahead and make an expansion tank out of PVC, I think this will work just dandy. And I''ll provide a vent that I can monitor just like you suggest (what a good idea!!). I truly appreciate the message board and value your input. How many gallons per minute live bait pump do you think is necessary for the 12v sea water pump? I notice in West Marine''s catalog they come in differing sizes? Thank you very much, Peter


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## geohan (Mar 8, 2000)

Peter I don''t recall the size of your engine so I''ll give you a per horsepower figure for cooling water requirements. The basic assumption was that about 1/3 of the fuel energy goes to mechanical output, 1/3 to exhaust gasses, and 1/3 to the cooling water. Ref: Marine Engines and Equipment, Robert Latham, Associate Professor, Engineering Dept., U.S. Naval Academy. This was (is?) a text used in USPS courses. All of this boils down to my design criteria of 5-Horsepower per gallon per minute of cooling water raised 25-degrees F. I believe this to be conservative. My exhaust felt warm but not hot and I can only guess at about 2 gpm flow rate for the 12-HP gasoline engine. A diesel engine cooling water requirement might be a bit higher but I''d guess only l5% or less. I used a 3/8" neopreme vane pump at about 1700 RPM but don''t know how much of the flow was being recirculated through the thermostat to maintain the 180-degree temperature. Regards, George


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## pjfsail (Mar 15, 2003)

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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## geohan (Mar 8, 2000)

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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## pjfsail (Mar 15, 2003)

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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## geohan (Mar 8, 2000)

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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## pjfsail (Mar 15, 2003)

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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## geohan (Mar 8, 2000)

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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## Nereus32 (Jun 23, 2002)

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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## pjfsail (Mar 15, 2003)

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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## pjfsail (Mar 15, 2003)

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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## Nereus32 (Jun 23, 2002)

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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## pjfsail (Mar 15, 2003)

Steve, thanks for your input. I truly appreciate you taking the time to answer. Peter


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