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slosharron 05-10-2003 08:19 PM

MD3B Volvo-Penta sea water to fresh water conversion
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.

RichH 05-10-2003 09:01 PM

MD3B Volvo-Penta sea water to fresh water conversion
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 ;-)

geohan 05-11-2003 09:23 AM

MD3B Volvo-Penta sea water to fresh water conversion
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

pjfsail 05-29-2003 08:41 PM

MD3B Volvo-Penta sea water to fresh water conversion
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

pjfsail 05-29-2003 08:42 PM

MD3B Volvo-Penta sea water to fresh water conversion
Rich, this makes good sense to me, thanks for your reply. Peter

geohan 05-30-2003 08:06 AM

MD3B Volvo-Penta sea water to fresh water conversion
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

pjfsail 06-02-2003 04:35 PM

MD3B Volvo-Penta sea water to fresh water conversion
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

geohan 06-02-2003 06:35 PM

MD3B Volvo-Penta sea water to fresh water conversion
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

pjfsail 06-05-2003 09:06 PM

MD3B Volvo-Penta sea water to fresh water conversion
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

geohan 06-06-2003 01:23 PM

MD3B Volvo-Penta sea water to fresh water conversion
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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