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Old 08-18-2009, 04:15 PM   #1
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Default Engine to heat water heater

Would anyone happen to have pics, or can more comprehensively explain, where the send and return from a 5.0L Merc i/o to a hot water heater exchanger gets hooked up? I can't tell from the manual's pic, and Merc tried to describe it over the phone but it's still unclear to me. Thanks, Tom. btw, the Merc is seawater cooled if that makes a difference.
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Old 08-18-2009, 08:25 PM   #2
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Default Re: Engine to heat water heater

for the hot water to go too the hot water heater...you need two hoses...there are 2 plugs on the engine...one at the intake manifold..and another that is on the top of the engine water pump....your going to need I believe 3/4" fittings that screw into the tops of the manifold and the water pump....4 ea screw down clamps....and 2 lengths of 3/4 in hose about 5ft long....(I'm trying to go off memory...which is dangerous at times...so..not sure if it's a 3/4 or 5/8th in. plug..take one off and go to an autoparts store..they will match it up for you)....on the hot water heater..there are 2 fittings that should be open....it doesn't matter which way they hook up to the heater........just as long as you have an in and an out....

the water pump at the front of the engine is going to be your intake...or suction of the system...the manifold is gonna be positive pressure......does that help??


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Old 08-18-2009, 11:41 PM   #3
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Default Re: Engine to heat water heater

Seapup, yes it does, thx; I know what has to be done, tubing and clamp wise, etc. although still fuzzy on where on the water pump and manifold. Here's a link to a pic of my engine; would it be too much to ask to download, and put circles where the connections go using Paint or similar program and repost? I know it's asking a lot, but appreciated; I know I can do this, as I've worked on plenty of stuff down in the engine compartment including the new hot water heater installation and fresh water pump. Tom. http://www.gmgsystems.com/Merc.jpg
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Old 08-19-2009, 04:32 PM   #4
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Default Re: Engine to heat water heater

tommy...
I don't have any editing capability here at work...so....suffice it to say that looking at your photo is about all I can do right now...however...if you look at the water pump on the engine..the one that is right in the middle of the front....on top of the pump is a square plug...can't miss it....that's where the suction is gonna come in..

next to the carburator...on the port side of the engine..there is a square plug there....those are the 2 places you can plug into and rig for your water heater......it's easy...make sure you add some silicone sealant to the threads of the new fittings....

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Old 08-19-2009, 09:25 PM   #5
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Default Re: Engine to heat water heater

If you run your boat in salt water, you may not want to connect the water heater. Most water heaters will not last with salt water running through them. I was told this is why my water heater is not connected. I have since upgraded to fresh water cooling and will be connecting my water heater.
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Old 09-07-2010, 02:09 AM   #6
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Here's a photo of the two connection points from the Mercruiser Service manual. The return point is very easy and is on the side of the thermostat housing as shown. The supply point is on the side of the circulating pump which is right behind the pulley in the center of the engine. (It's not really a pulley, the belt goes over it on the flat side.)

Good luck.

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Old 09-07-2010, 03:56 PM   #7
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I would not connect it if it is in salt water. I believe most water heaters have aluminum internals and would not last long with salt water. Otherwise, use this as a reason to install a fresh water system to your engine. I did mine myself for about $600. They also make a thermostat valve for the water heater so you don't heat the water to 175 degreesF or more. You don't want scolding water coming out.
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Old 09-07-2010, 10:17 PM   #8
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Can you pump the closed coolant through the hot water heater? I thought it was raw water that was pumped through there. to play devil's advocate, if it is raw water and the hot water heater 'goes' you could be flooding the engine compartment with raw water. If it is the closed cooling side, and the hot water heater goes, you would only flood the contents of the coolant, so the upside would be a limited amount flooding the boat, on the downside, there would be no coolant left in the engine and overheating would result.

I didn't reconnect the hoses to allow the engine to heat the hot water heater after I repowered. I simply didn't trust it enough and the engine was more important to me than a little hot water. I use the generator for 15-20min./day to heat the hot water in the tank when I'm not on shore power and it works fine. I'm not saying I'm right, it's just a thought.
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Old 09-08-2010, 04:30 PM   #9
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When you say "if the hot water heater "goes"...it depends on what part "goes". I can't see you flooding the bilge in any event. If the heat exhanger coil springs a leak, then you'll be pumping raw water into the hot water tank...it'll just fill up and then stop. If the actual hot water "tank" springs a leak, it is isolated from the raw water. So in either case, you can't flood the engine compartment.

My case is a raw water cooled so I don't know if the tank should be heated by the raw water or the closed system. I imagine that the closed system would be hotter and therefore do a better job at heating the water.
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Old 09-08-2010, 05:37 PM   #10
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OK, that makes more sense. If the coils carrying the heated cooling water run inside of the tank, then a rupture of the coil would only cause a limited leak into the pressure water system. Not ideal, but better than what I was picturing. Thanks for clarifying. That actually makes more sense now that I think about it.
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