Freshwater Cooling Conversion on 350 / Seawater Pump

[SeattleMatt]

Hello, <br /><br />We have made a freshwater cooling system for our 350, . The question I have is for those out there with freshwater cooling on 350's:<br /><br />In the manual it shows an extra pump (seawater pump?) inline with the drive impeller up in the engine compartment. Is this pump required for a 350 with freshwater cooling? Is there not enough flow from the impeller in the outdrive?<br /><br />The reason I ask is that after we have the whole system together, filled with proper coolant, with thermostat removed, and muffs feeding the leg at idle, the engine gets up to about 200 degrees and rising. Could this be because there is just not enough flow from the muffs? Do I need to buy a "seawater pump"?<br /><br />Thanks,<br /><br />Matt<br />Seattle, WA<br />1978 Reinell 6m

 

[Boomyal]

Re: Freshwater Cooling Conversion on 350 / Seawater Pump

Impeller volume is sufficient, from OMC, to cool a 351W Ford. I'm not sure about it if you are cooling your manifolds as well. You could still try it. At least in part, the H\E size would be important. Here is a picture of mine cooling a 302 only. Reports have it that there are smaller H/E's out there that are insufficient.<br /><br />

 

[SeattleMatt]

Re: Freshwater Cooling Conversion on 350 / Seawater Pump

Great Picture, The whole system is homemade. The heat exchanger is quite large, 21" long and 8" diameter with 14 stainless rods through it. I will put picutres up for it soon.

 

[yoced]

Re: Freshwater Cooling Conversion on 350 / Seawater Pump

What **have** you got going here? <br />Are you cooling the manifolds?<br />Is your heat exchanger above your thermostat housing?<br /><br />Cooling with stainless rods? I don't quite understand your construction.<br /><br />A typical 5" H/E bundle will have over 200 copper cooling tubes. The name of the game here is surface area and contact, slow and steady like a good dance. The longer the hot water stays in contact with cold metal the better. <br /><br />Also, stainless is not near as good at transfering heat as copper. I would also question the schedule tube you are using even if it were copper - too thick a wall cannot help you here. <br /><br />Keep in mind also that most heat exchangers are AT LEAST two pass systems - in other words, the water goes down one way and back the other - doubling the length of the heat exhanger. <br /><br />A typical 5" bundle then may have over 40" of travel along almost 100 tubes (100 one way over 20", then 100 the other way over 20")<br /><br />Looking forward to your pics - always nice to see something completely different...

 

[SeattleMatt]

Re: Freshwater Cooling Conversion on 350 / Seawater Pump

Okay, after the pictures are posted you may think I am in fact crazy. Important Facts:<br /><br />The seawater flow comes from the drive impeller through the transom to the heat exchanger it then flows out to a T connection where it spits off and goes out the the exhaust elbows.<br /><br />The closed coolant flows out of the heat exchanger into the water pump which circulates the coolant through the engine, power steering heat exchanger, and finally the lower portion of the exhaust manifolds. A 180 thermostat (not currently installed) will allow the water to return to go back to the heat exchanger after this flow.

 

[SeattleMatt]

Re: Freshwater Cooling Conversion on 350 / Seawater Pump

I think the problem is that there is insufficient flow of seawater. The heat exchanger gets very hot, indicating that it is doing its job and that the coolant is flowing through it. Also, the water that flows out of it is cool. I guess I'll know more when I get it to the water.

 

[Boomyal]

Re: Freshwater Cooling Conversion on 350 / Seawater Pump

If it doesn't work, scoot right on over to Bellingham and see the boys at San Juan Engineering. They'll fix ya right up.<br />Be sure to tell em that Boomyal sent ya!

 

[navigator336]

Re: Freshwater Cooling Conversion on 350 / Seawater Pump

If the raw water is cool exiting your HE and the coolant is hot, the HE is not extracting enough heat and your immediate problem is not lack of raw water flow. As Yoced pointed out, with 12 SS tubes, you do not have enough surface area to transfer the heat. Yoced also pointed out that SS is not as good a heat conductor as copper. If 12 tubes filled an 8 inch diameter HE body, the tube diameter is way too large. If you go back and remake it with 1/4" or 3/16" diameter copper tubes, that heat exchanger will cool a diesel engine and then some (with enough raw water flow).

 

[Peter J Fraser]

Re: Freshwater Cooling Conversion on 350 / Seawater Pump

Another factor which you have not mentioned is whether there are baffle plates fitted on the tube stack to force the FWC coolant to take an "S" flow pattern as the water travels from one end to the other of the HE. This increases turbulence in the water flow and assists with heat transfer to RWC side.<br />Yoced is right about the tube count / size.<br />Good luck.<br /><br />Peter

 

[Chris1956]

Re: Freshwater Cooling Conversion on 350 / Seawater Pump

Slow boy, I have been advised by a Mercruiser dealer that V-8 sterndrives need a through-hull fiting and auxillary raw water pump to effect a closed cooling system. The outdrive impeller's cooling water flow was insufficient.

 

[mikeneal]

Re: Freshwater Cooling Conversion on 350 / Seawater Pump

I know very little about the heat exchangers used for closed loop cooling. But I am a mechanical engineer and recall a bit about tube and tube heat exchangers. The 12 stainless tubes inside a 8 inch tube is not even close to the effiecncy of the smaller copper setup. Like everyone said surface area is the name of the game. I bet the water flow is not the issue..try to geta used heat exchanger off ebay or somewhere. If I was you I would just buy one, making a good one is lots of work and I love to tinker and make things.

 

[mikeneal]

Re: Freshwater Cooling Conversion on 350 / Seawater Pump

Opps I forgoet, Like I said I don't know much about marine heat exchangers but I but they are made from bronze and not copper as it has a much greater resistnace to the the sea water...justa note.