Ateood water heater disconnect question

LUnaCY

LUnaCY

Active Member
Aug 28, 2018
206
Afton, MN
Boat Info
310 Sundancer 2002
Engines
Mercruiser 5.0 MPI Bravo III
936BD997-9240-445D-9485-019D89B3D836.jpeg
I have an Atwood water heater with both electric and engine heating (apparently). The water heater will be replaced sobIm fully bypassing it. I connected the red to blue, cold water feeds the hot water lines now.

How are the two engine lines affected? Ive disconnected them but dont know what water is in there? Is it from the water heater that flows by the engine to heat or is it engine water that flows through the water heater casing?

Should I just tie the two together to create a loop outside of the heater and isolate the engine? If so can I run the engines like that until I replace the heater?

The two black hoses are in the pic and disconnected.

Thanks!
 
You answered your own question.... Should I just tie the two together to create a loop outside of the heater and isolate the engine? If so can I run the engines like that until I replace the heater? YES And it's anti-freeze running in there.
 
Sorry, Im mostly getting it. I didnt know my engine had antifreeze. Is that a small closed loop from engine to water heater with no purpose for the engine?

Or, if its a raw water cooling system (freshwater MN boat) perhaps it runs lake water through the heater? I guess I could fire it up and see what blows all over the bilge. lol
 
Last edited:
LUnaCY said:
Sorry, Im mostly getting it. I didnt know my engine had antifreeze. Is that a small closed loop from engine to water heater with no purpose for the engine?
Click to expand...

the only purpose is the heat the engine is producing is to heat your water in the hot water tank...
 
Close it off and you'll be fine. Also check your gear lube monitor. It looks low.
 
Low it is. Thx! First big boat and on a steep learning curve...hopefully. Bought all the SAE 90 HP to change the gear lube, but saw that it is blue, but the monitor looks black like motor oil. Didnt want to put the wrong fluid in so was waiting a week until its pulled out and i do the complete change.
 
LUnaCY said:
Sorry, Im mostly getting it. I didnt know my engine had antifreeze. Is that a small closed loop from engine to water heater with no purpose for the engine?

Or, if its a raw water cooling system (freshwater MN boat) perhaps it runs lake water through the heater? I guess I could fire it up and see what blows all over the bilge. lol
Click to expand...
Sorry for the bad info about antifreeze... I have boated on salt water my whole life and assumed (I know-lol) that you had a closed cooling system.
 
No problem! Everyone pitching in really helps. Im use to being able to rebuild systems, from hydraulic to electrical to pneumatic. That’s where I’m going with this eventually. Still wondering when I connect those two hoses and create a loop on the engine, is anything circulating there? I believe raw water, so I do need to fill them with antifreeze when it’s winterized. Also, what drives the pressure there? The same impeller as the raw water intake? Wouldn’t that make that loop a raw water loop and now an empty closed loop? Mercruiser manual isn’t in depth enough.
 
Although this was answered above, it's not clear that you completely understood, yet... so...

-- From the picture you posted of your engine, it's clear you have a raw water cooled engine.
-- Raw water circulates through those (unattached) black hoses to the HWH and back.
-- Raw water will continue to circulate through them when you barb them together... it is really quite simple - think of that system as a circle/loop.
-- You can barb the two together, or even remove them from the engine and plug with garboard drain plug. For winterizing, through, you don't need to even barb them - just secure higher than the engine so the AF doesn't drain out.
-- The same pump that circs water through the engine circs water through the HWH - just follow the hoses to see where they go... the circ pump. Things will make a lot more sense if you take a few minutes to physically look at how it's plumbed. Don't worry - it's not rocket science.
-- Yes, you will push antifreeze through those hoses when you pour AF into the t-stat hoses.
-- Gear lube MUST be the Hi-Performance synthetic Merc stuff for B3's. Couldn't tell you what is currently in there... might just be old.
-- Did you also buy new drain/fill screw washers for the outdrive?

-- Buy the service manual - that's what it's meant for. But it's also not meant for the average Joe - it assumes the reader has a good, working knowledge of systems to begin with.
 
Thanks Lazy Daze! So when I change the outdrive gear lube replace those with new washers/plugs? Will do. Yes I have the hp gear lube.
 
LUnaCY said:
Thanks Lazy Daze! So when I change the outdrive gear lube replace those with new washers/plugs? Will do. Yes I have the hp gear lube.
Click to expand...
In reality, they shouldn't "need" to be replaced every year... but for the couple bucks it costs, to save the couple thousands it would cost to replace the drive... better safe than sorry.
 
Take a picture of the top of the engine cover that has your engine Serial Number.

Do a search for your engine manual using the S/N and you might find a .pdf copy for download.

That's how I found mine.
 
I was finally able to remove the water heater with only needing to remove the port engine oil filter for clearance. Of course it looked like this at the time. Patience low as winter approaches.
076DA48E-02C1-4C5C-BF9F-A674D70C6046.jpegCED8A3D7-2F44-41BD-8259-F627B4B25D6C.jpeg

Now to replace it in the spring. Any preferred brands over Atwood? If it were 12” tall or wide I could get it back in simply, but I dont want to replace with junk.
 
Isotherm makes some narrow ones. Look at those.
 
If that is the original Atwood, it lasted 16 years. Would hardly call that junk. If they still make that model buy another one just like it.
 
I didnt mean the Atwood was junk. I meant to avoid junk suggestions simply because they were smaller and avoid me some labor on the install.

Im leaning toward the Atwood and completely disassembling it to install it, then reassemble. Its only 16 or so small hex screws. Seems easier than moving the remote oil bracket and likely the vacuflush.
 
I got a new Atwood a few years ago. It was very light. Got same size and it fit as per the old one. Original one had the engine lines on one side and the electric on the other. New one had both electric and engine on the same side. Is the plywood on top original?
 
Obviously do what works best for you. But since you have outdrives, you have lot's of space in there to work - I'd probably opt for moving the vac tank as that's actually pretty quick to remove. It's not really "screwed down" - you should notice that it's just wedged in place with thimbles - you only need to remove two of the thimbles, then it will slide out from the other two. The hoses can be a bit stiff, but they're doable, as well (if you even need to remove them, that is). To me, that just seems to be simpler than trying to put the heater back together in that confined space. But either way will work.

Plywood on top is original. Often, but not always, that's where the fresh water pump got mounted.
 
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