Hot Water Heated by the Engine

[SteveK]

Here I am confused.

If I was to do this, from which system would I draw off 1/2 a gallon to compare it's density to that of the cold potable fresh water from the tank?

one pot of just hot water tap, one pot just cold water tap.
IMO, antifreeze leak into HW tank where there is inlet cold water pressure will not back feed into the cold water tap.

 

[luna]

I would suspect the raw water heat exchanger. But to be sure how about drawing off 1/2 gal and use a hydrometer to see if it different from same amount of cold only.

Given ancora's symptoms, a prodigious loss of coolant, I would also suspect a breech in the engine's coolant to raw water heat exchanger. This could result in large volumes of coolant abandoning ship by way of the exhaust system.

What confuses me is how can I be sure that I have a breech in raw water heat exchanger simply by measuring the densities of the hot and cold water in the potable water system?

I would think a more revealing test would be to drain down the raw water side by removing a hose, add a bit of dye to the coolant if required for visibility and then apply 7-10 lbs of air pressure to the coolant side. Then watch for the dyed coolant to come out the open end of the raw water hose.
If the pressure holds when cold, mount a couple of 1500 watt space heaters next to the heat exchanger, cover it with a large towel and see if 170º F, changes anything.

 

[SteveK]

Luna, maybe you need to re read. I was replying to do with concern of coolant in the hot water tank, offering a way to test fresh water from the tank.

 

[luna]

Stevek, I don't need to re-read anything.

Why if you were replying to a concern about coolant in the water heater's tank did you suspect the engine's raw water heat exchanger? Does a breech in the raw water heat exchanger automatically result in contaminated potable hot water? How?

 

[SteveK]

I'm losing coolant at a prodigious rate from the engine that is hooked up to the water heater. Is it possible the coolant is going into the 12 gallon water heater?

@luna let me re read for you

 

[luna]

SteveK,

If it was all about the potable water's water heater tank, then why did you bring the raw water heat exchanger into the equation? And then pronounce that "to be sure".... do this!

These are your words.

"I would suspect the raw water heat exchanger. But to be sure how about drawing off 1/2 gal and use a hydrometer to see if it different from same amount of cold only."

 

[SteveK]

SteveK,

If it was all about the potable water's water heater tank, then why did you bring the raw water heat exchanger into the equation? And then pronounce that "to be sure".... do this!

These are your words.

"I would suspect the raw water heat exchanger. But to be sure how about drawing off 1/2 gal and use a hydrometer to see if it different from same amount of cold only."

Maybe the person I replied to understood me.

 

[luna]

And maybe that person didn't.

Let's hope that person is not replacing his raw water heat exchanger solely because there is a density difference between his hot and cold water. That would be silly.

From this vantage point ancora should pressure test the raw water heat exchanger to determine if there is a breech.

 

[ancora]

Tested the water and it was okay, so I'll have to bite the bullet and go with the heat exchanger.

 

[SteveK]

Tested the water and it was okay, so I'll have to bite the bullet and go with the heat exchanger.

If you can take it out yourself and then take it to a rad shop, they can test and possibly fix. Otherwise swap out with a new one.

 

[ancora]

A new one is not possible as the engine is a Volvo. Volvo enjoys having the worst customer service in the industry. Parts are difficult to find and cost triple that of Cat or Cummins. After market suppliers are discouraged by threats from Volvo. The heat exchanger I have now is a used one I bought off EBay. Did not last six months. I can only hope it can be fixed.

 

[DDW]

I've not found Volvo much more difficult or expensive than Cummins. But one thing I have done is order Volvo parts from Sweden or the UK. Often much less expensive (like 1/2) even when shipping is counted for the same part.

 

[O C Diver]

A new one is not possible as the engine is a Volvo. Volvo enjoys having the worst customer service in the industry. Parts are difficult to find and cost triple that of Cat or Cummins. After market suppliers are discouraged by threats from Volvo. The heat exchanger I have now is a used one I bought off EBay. Did not last six months. I can only hope it can be fixed.

Did you try Seakamp or mr. cool? Both appear to build Volvo heat exchangers.

Ted

 

[Hawkshaw1]

I just wanted to report back that I have not made any changes to the coolant flow valves to the water heater. The holiday was busy, and I didn't have any downtime AND I am not sure how old the water heater is. If it's original to the boat, I may replace it even though it works just fine at present.

I had another thought, too. If the PO winterized the plumbing system but still used the boat in some winter months, that may be why the valves were in the off position. The boat went mostly unused for two years before I purchased it.

Thank you for all the replies and discussion.

Hawk

 

[Cigatoo]

Just to clarify.

You have 3 main systems in your boat

1. Potable water which is in your hot water tank and faucets.

2. Engine coolant / anti freeze which flows through your engine and engine heat exchanger. (The heat exchanger replaces a radiator that you would have in your car) The same engine coolant also flows through a coil in your hot water heater and heats up the potable water in the tank. The valves in your picture control the engine coolant that flows through your hot water heater. (On or off)

3. Raw water cooling is seawater that flows through your heat exchanger to remove the heat from the antifreeze that also flows through the heat exchanger as mentioned above.

Having said that when the owner winterized the boat he ran anti freeze through the raw water system and potable water system. (1. and 3. above) The engine coolant isn't touched as long as it is 50/50 antifreeze just like in your car.

If the owner ran the boat after he winterized it he would have to re introduce anti freeze into the raw water system

 

[Cigatoo]

This post was a mistake . Please disregard

 

[ancora]

We "called the guy" and he shows up with a clipboard (not a good sign) and proceeds to go into the machinery spaces. Eventually he comes out and tells us he will send us an estimate of what needs to be done, and leaves. Thoroughly pissed off, I started to look for where the coolant was going. I found that one of the hoses from the engine to the water heater was leaking coolant into the sump. The hoses go through two bulkheads, so the leak was not visible. Funny things is, I bought a 50' reel of hose some time ago to replace the old with the new but never got around to it.
PS That leak detector dye really works.

 

[ancora]

I "called the guy" and told him my problem. He said he would pressure test the heat exchanger. Shows up with only a clipboard (not a good sign) goes into the machinery spaces, looks around, comes back out and says he will send us an estimate of the work required. I had previously added leak test dye to the system, and started searching for where the coolant was going. One of the coolant hoses to the water heater is leaking. The hoses go through two bulkheads making the leak hard to see. No big deal, I'll change both hoses while I'm at it.
Conclusion: In another month, I'll be 90 years old and a better mechanic than "the guy."

 

[Marco Flamingo]

One of the coolant hoses to the water heater is leaking. The hoses go through two bulkheads making the leak hard to see.

I've used this stuff to protect electrical cables and comply with ABYC guidelines. It is very durable and abrasion resistant. It "clings" to the cable/hose by wrapping around so tight. I've been meaning to go back and do all of my heater hoses at abrasion points where they run to the water heater and to the Red Dot heater. I'm sure I can put a length on the hose and then push it through any bulkhead penetration.

 

[ancora]

I've used this stuff to protect electrical cables and comply with ABYC guidelines. It is very durable and abrasion resistant. It "clings" to the cable/hose by wrapping around so tight. I've been meaning to go back and do all of my heater hoses at abrasion points where they run to the water heater and to the Red Dot heater. I'm sure I can put a length on the hose and then push it through any bulkhead penetration.

That will certainly do the job. Thank you.

 

[Mako]

Make sure you purge the line with a hose, especially since you heard the gurgling noise. When I was younger and dumber I burnt out a brand new water pump because of this.

 

[Capt Ray]

Agree with Red Rascal. An objection that some have is with scalding. Engine coolant temp it typically hotter than HW tank.

A mixing valve solves for this. Or awareness and caution.

Yes. Engine's thermostat is 180F. Hot water heaters on boats are usually small, and the water is HOT... so that the proportion of hot water is small for showers or dishes. I agree, it can thus last a long time! AND I agree, your crew should be made aware that 180F can scald you.

In public places like school cafeterias and restaurants, the kitchens need 180F to run their fast-short cycle dishwashers, but a mixing valve is plumbed in for the showers and bathrooms. This is not usually done on boats... as the crew and visitors can be "trained" accordingly.

 

[SteveK]

140* is the usual hot water tank temp. If 180* goes through long enough does your relief valve drop water into the bilge?

 

[Steve DAntonio]

Lots of interesting comments here, however, responding to the OP. Making domestic hot water with engine heat is very common, it's otherwise wasted heat. The isolation valves enable you to isolate the WH in the event of a leak in the WH's heat exchanger or the plumbing. Cracking one will not allow the system to work, at least not properly, they both need to be open.

If your WH is connected to your engine, it must also include a tempering or mixing valve. Because coolant is traveling to the WH, it's possible for it to heat domestic hot water to nearly the temperature of the coolant, which could be a scald hazard, and some plumbing used with domestic HW isn't rated for that high a temperature. Additionally, the cold inlet on the WH should have a check valve. This prevents bacteria that may form in a cold (one that is off line) WH from leaking back into the potable water system (or at least that's ABYC's logic). And, once you install the check valve, you also need to install a small accumulator tank after that valve, either between the check valve and the WH inlet, or on the hot outlet, to allow for water expansion when heated.

More here Water Heater Primer | Steve D'Antonio Marine Consulting

 

[JACrowley]

I have a Mainship 390. The hot water heater has hoses from the engine, but the water doesn't heat up unless the water heater is on shore power or generator power. I investigated today and found two small valves that control the engine coolant flow to the heat exchanger, and back, to the hot water heater. Both valves were turned off. I cracked one of the valves, and I could hear coolant "gurgling" in. I would like the engine coolant to heat our water while underway (I think).

I am hesitant to open both valves. The previous owner of my boat had passed away before I bought it, so I don't have any direct information about it.

Does anyone have an opinion about why these valves would be shut off?

Does any have an opinion about engine coolant heated water (pros or cons)?

Thank you,
HawkView attachment 169744View attachment 169745

I have a similar arrangement in ,y Albin 32+2 with Cummins 6BTA. I concur with previous posters as to logical reasons to have it shut off. Here's another one; while underway your hot water temp is not regulated, so what comes out of the tap is going to be something close to engine coolant temp- around 180*F, in my case. The first time I blasted the hot water and thoughtlessly stuck my hands under the tap I was SHOCKED at the temp. If you have children aboard it may be a safety concern. I keep mine on, but issue warnings to passengers to always start with cold and add in the hot.

 

[Mako]

If you have children aboard it may be a safety concern. I keep mine on, but issue warnings to passengers to always start with cold and add in the hot.

I vote negative on that. It is absolutely a MUST to have a tempering/mixing valve on the output of the water heater. They are not expensive nor difficult to install - just do it.

 

[ancora]

I put some leak detector die into the heat exchanger and found one of the hoses going to the water heater had a leak.

 

[Cigatoo]

I have a similar arrangement in ,y Albin 32+2 with Cummins 6BTA. I concur with previous posters as to logical reasons to have it shut off. Here's another one; while underway your hot water temp is not regulated, so what comes out of the tap is going to be something close to engine coolant temp- around 180*F, in my case. The first time I blasted the hot water and thoughtlessly stuck my hands under the tap I was SHOCKED at the temp. If you have children aboard it may be a safety concern. I keep mine on, but issue warnings to passengers to always start with cold and add in the hot.

Go with a mixing valve. Easy install, makes things safer, and saves hot and cold water. All for a hundred bucks or so. Shark bite or garden hose connections. Which ever is easiest for your particular situation.

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