water heater engine coolant bypass valve?

[buddy0]

What is this and do I need it?

It looks to me like it has the engine coolant return hose going into the bottom and then out of the end back to the engine. It has the fresh hot water output going into the left side and out of the left side to supply hot water to the boat.

I am guessing that this is some kind of valve that senses the temp of the water and opens/closes the coolant back to the engine - thus controlling engine heating of the hot water.

Is this correct? Is this necessary? I am coming up empty looking for this online and can find no reference to it in new water heater information.

This is on a 2005 Hunter 33. The engine has not heated the hot water since I purchased the boat and I suspect this valve. My tank is now leaking so I need to replace it so its forcing my hand in figuring this out. Do I need this in a new tank install?

[Calif.Ted]

I think that is a "tempering" valve designed to prevent the domestic hot water from being hot enough to burn skin. Isotherm water heaters used to come with them as standard equipment. What kind of heater is it, mine have always been in a place where only a direct replacement would fit. Also called "anti-scald" or mixing valves sometimes.
Common among all boat heaters is an air lock in the coolant lines between engine and heater will prevent it working on engine heat. Some will have a "bleed valve" at the high point, others you must figure out a way.

[buddy0]

It is a Force 10 model 405001.

Is this feature built into the newer units like the Kuuma. I don't see any mention of it. There must be something to keep the water from getting to 160+ degrees.

[Calif.Ted]

I remember them as built in to some units, the attached manual from Isotemp at figure 3- 4 shows models with or without the mixing valve. I've only had Seaward Hx which do not have them and the water can be too hot and care must be used. It's safer with one, no doubt.
https://www.westmarine.com/on/demand...4-_-4725201303

[buddy0]

Thanks for the info.

I also found the Kuuma manual and they explicitly warn that the water can reach 170+ degrees - the coolant temperature - and you might want to add a mixing valve.

Not that it's important at this point, but I dont think what is on there now is a mixing valve because there is no fresh cold water connection. I think it is another type of device that limits the temp of the water in the heater by closing the coolant loop.

[Calif.Ted]

Could well be correct on that, I've read of other methods to limit temperature as you suggest but have no personal experience with them.

[NorthCoastJoe]

It is to limit the water temperature in the tank, cutting off the flow of engine heat. Nothing complex just stops the water from getting too hot. If you bypass it you will have hot water at whatever temperature that the engine coolant is. Normally 170 to 190 degrees F. Just so you know water over 120 degrees F will cause burns.

[s/v Jedi]

I still don’t understand how the engine coolant connects to this and you still live to tell after it mixes with the fresh water supply…

[pjShap]

The engine coolant is in a heat exchanger loop, no contact with the fresh water. The water can get to engine coolant temperature. There's usually a tempering valve on the hot water outlet that sets the temperature of the hot water being dispensed by mixing with cold water as needed.

[s/v Jedi]

Originally Posted by pjShap

The engine coolant is in a heat exchanger loop, no contact with the fresh water. The water can get to engine coolant temperature. There's usually a tempering valve on the hot water outlet that sets the temperature of the hot water being dispensed by mixing with cold water as needed.

But OP says the coolant connects to the tempering valve…

[pjShap]

Originally Posted by s/v Jedi

But OP says the coolant connects to the tempering valve…

You're right, but it doesn't make sense to me. Coolant can't connect to a tempering valve. It can't add cold water to the coolant. Also, looking at the photos, I don't see any temperature adjustment knob. I suppose it could be a thermostat that limits the internal heat exchanger temperature. OP said it leaks and needs replacing. Any replacement unit should have clear installation instructions.

[Bowdrie]

It would probably be more understandable if a pic showed a right-side-up view of the entire face of the heater with all hose connections.

[Sailorichiban]

Hello All,
In my youth everyone knew or else learned to be careful of scalding hot water regardless of from the stove or tap. The first house in my remembrance had only a well pump that often worked, unless it froze. Don’t forget to drain your water before the freeze! No hot water heater, only heated water from on top of the oil furnace, the stove or fireplace.
Nowadays too much interference due to regulations designed to protect us from ourselves, as if common sense no longer exists, and forget about the additional cost. Actually somewhat insulting, over regulations.
After having a wife with very long hair, who could easily use 6 gallons of steaming water for washing, I don’t appreciate tempering valves. Often I would run my engine to increase the amount of hot water just for her showering, which was actually something I did every day anyway to charge the batteries at the same time.
One of the modern conveniences which seems to me to have been around for as long as I can remember are mixing valves of some kind for every shower excluding cold water only fixtures.
Only goes to show pluses and minuses exist in all areas. My suggestion: use common sense in all things.

Best to all!

[buddy0]

A couple of more picture just to close out this thread.
One with the valve disconnected and spun around so it is upside down and the other showing the end that connects to the coolant line from the engine.
There looks like a check ball in the end that is frozen in place, so the coolant wasn't allowed to flow through the heater, and is why I was not getting hot water from running the engine.

I don't think they make these anymore.

Heater is replaced with a new one, with standard hookups, and is working fine.

[lifeofreilly57]

Most engines run at 180 degrees, much too hot for your shower hot water, also that temperature will usually trip the overtemperature protection switch on the AC side of your water heater. A temp controlled bypass is a great device to have on your water heater.