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Water Heater hoses

Sep 11, 2019
Hunter 386 Lake St. Clair
Hey Guys, I have 2 hoses that run from our Water Heater tank to our engine. Note 2 pictures. What runs through these lines, antifreeze or water? is this fluid isolated from the hot water tank via a heat exchanger? What maintenance and how do you do it? I note 2 connection caps, 1 at engine, 1 at hot water tank. Anything need to be done when winterizing? Thank you!


Jul 7, 2004
Hunter 30T Cheney, KS
Here's a link to my heat exchanger flush/winterizing thread. The closed system gets pretty gunked up over time. I bought a refractometer to check my antifreeze mix when I was done with the flush.
Sep 25, 2008
Alden 50 Sarasota, Florida
Justin’s link is a good description of how to flush the cooling system and heat exchanger in the hot water tank. To state the obvious, winterizing the hot water tank and potable water system is an essential separate process not to be confused with the above. They are mutually exclusive steps.
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Jul 7, 2004
Hunter 30T Cheney, KS
That's an important distinction Don.
I added diverter valves to my hot water tank (another thread) supply lines. So I just bypass and drain the tank. The rest of the water supply system gets the pink stuff.
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May 21, 2004
Jeanneau Sun Odyssey 409 Mt. Sinai, NY

The hoses you show contain engine coolant. They go to the heat exchanger INSIDE the water heater. That's how the engine can heat your domestic water.

Regarding winterization, as long as your engine coolant is in good shape your are set for winterization. Note that engine coolant, like all fluids, requires a change after a certain interval (you decide). Personally, I like to change coolant every 3-4 years or so. If you don't know when the coolant was last changed, I suggest changing it. Be aware that the lines to / from the water heater tend to develop an air bubble when you change the coolant to be prepared to 'burp' the lines a few times.

Dec 14, 2003
Hunter 34 Lake of Two Mountains, QC, Can

''Regarding winterization, as long as your engine coolant is in good shape you are set for winterization''.

Gary, you need to understand that Barry is talking about the antifreeze that is part of the loop between the engine and the heat exchanger INSIDE the water heater. The water heater itself needs to be drained. No need to put any pink stuff in it. In fact, if you do make absolutely sure you do not run the engine or turn on the AC power to the water heater. When heated, the pink stuff will turn into cotton candy and ruin your water heater.
Jan 7, 2011
Oday 322 East Chicago, IN
As said, you are talking about 4 different systems…
1) water heater / engine circuit…engine anti-freeze circulated through engine and the hoses take the hot AF to the heat exchanger in the water-heater…this gives you hot water when motoring…no “winterizing“ of this circuit is required.

2) Engine raw water system…lake water pumped through the engine Heat Exchanger, and then out through the engine exhaust. This circuit needs to be winterized…pink AF sucked in the raw water intake, engine on, and run several gallons through the engine. Pink AF will flow out of the engine exhaust.

3) potable water system (red and blue water lines in your photo). Usually you have a water tank, water heater, water pump, faucets, all tied together with the red and blue lines For hot and cold water. This circuit needs to be winterized as well.

I generally drain my water tanks, drain my water heater, bypass the water heater, then remove hose from water tank, put the end of the hose in a gallon of pink AF, and turn on water pump and open each faucet (Hot and cold). I have 2 water tanks, so I repeat the process on the 2nd tank.

4) Head/toilet - also needs to be drained and winterized…I pour pink AF into the water intake strainer, while someone This pumps AF all through the toilet, hoses, valves, toilet rim, and pushed it to the holding tank. It can stay in the holding tank all winter.

Don’t just dump AF into the toilet bowl and pump it dry…it won’t get all of the valves and cavities in the toilet.

5) Finally, I usually dump some pink AF into my bilge…if I get any water in there, I don’t want it freezing solid and cracking something….so a bit of AF should keep things slushy at worst if I get water in the bilge.