1994 390CPMY 11 gallon water heater

[tonyiiiafl]

I have the original (Seaward?) water heater, 11 gallon. It is mounted under the dinette next to the salon A/C. I know it has a heat exchanger, as we get hot water while we are underway. HOWEVER, I can’t see where any water lines come from the engine ( fresh water heat exchanger) to the water heater. AND I have looked under the seat of the dinette and could not see any hoses. Any ideas from a personal experience? Also, I am thinking of replacing with one with a mixing valve. Anyone ever replace with an isotherm? I am a tad concerned about the if a failure is long overdue?

Thanks as always!

Tony

[Midnightsun]

The hoses should be quite evident. As long as there is hot water in the tank you will get hot water from the tap while under way. I have no engine/exchanger connection and have never run out. I do run my generator for breakfast, lunch and supper while on the hook so this does heat it up. Regardless, never ran out.

I see no point in going with an Isotherm. I replaced mine with the same brand as the original a few years back just for the convenience of not having to change fittings and or extending cutting lines and moving bracket making new holes, leaving old one to plug up.

That being said I did replace it with one that has a heat exchanger as they are more common than without and are cheaper due to supply and demand. Heat exchanger is not hooked up and does not need to be.

[tomschauer]

The engine coolant connections are in the rear (opposite of domestic water) on my 355. If the tank isn't leaking I personally wouldn't replace it. Its a stainless tank and if it is flushed at least once a year (when winterizing) to get any deposits of the bottom, it should last darn near forever.
If your worried about it, pull the element and look inside with a borescope.

[Midnightsun]

Its a stainless tank and if it is flushed at least once a year (when winterizing) to get any deposits of the bottom, it should last darn near forever.

The exterior is stainless, the tank is aluminum and is very prone to oxidation, they have a limited life span as most do not even have anode protection.

See here. viewtopic.php?f=11&t=3660&hilit=heater

[Viper]

Ya the exchanger hook up is usually on the back of the units I've seen on 355s. If yours is hooked up, they'll be coming off the front of the starboard engine. There are a few spots they can be connected to but just look for heater hoses leaving the engine and heading to the starboard side and forward if I remember correctly. The lines will be full of coolant. If you pull a model number off the heater, use it in a Google search and you should be able to determine if there are exchanger ports on the back of it, I know it's a hard spot to get at and physically check.

[Midnightsun]

I should have mentioned the Isotherm does have a stainless tank and may be a good choice if you have the space available for one as the dimensions are quite different from the conventional square tank.

[tonyiiiafl]

Thank you. I am going to have to do more investigation. I am sure I have a heat exchanger as when we were on the hook and the genset wasn’t cooperating, I did start the engines to charge the batteries and also made hot water. I guess I am just not looking hard enough. I am heading down this weekend to start my launch prep and need to take a lot closer look.

[Viper]

I think the hardest part I can remember getting to on the tank once you remove all the other hardware in that space to get the tank out, was getting at the rear bracket screws fastening the heater down. Take a close look at this and determine if getting a tank with side mounted brackets would be better because getting those screws back in behind the unit will not be easy either. The caveat here is that the side mounted bracket option may make the unit too wide to get through the hole. Keep this in mind when you're pulling the current unit out to see what you have to work with and purchase accordingly. It may be that your current setup is easily accessed.

There are a few ways to deal with all the coolant in the lines and tank. I like to first remove the lines from the engine. When you remove each hose, hold it up high and be ready to cap off the engine ports. Have a pail ready, place one hose in the pail. Once the coolant starts running, it should siphon the contents out of the tank's heat exchanger. You can blow through the other hose to ensure you got everything. This will minimize the mess you make when you remove the hoses from the tank and when you tilt the tank to get it out of that space. After hook up, run the engine for a while, then top up with the coolant you put in the pail.

Make sure your hot water tank is full of water (purge hot water faucets) before you turn the heater on and test.

Let us know how it goes.

[tomschauer]

Hans is correct, the Seaward does have an aluminum tank. I thought for sure it was stainless.
I replaced the element and thermostats a few years ago on my 1998 vintage seaward and looked inside with my borescope, all was clean and shinny. Looked like stainless.

[tonyiiiafl]

DIdnt see a thermostat on mine. Hot as Hades. But holds the temp. It does cycle on and off though..