Hot Water Heated by the Engine

[Hawkshaw1]

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,
Hawk

 

[RedRascal]

It's a pretty easy way to heat up the water underway without the need of a generator or shore power when you dock or anchor. Depending on the tank water can easily stay shower hot for 12+ hours. As for the valves being off here are some thoughts:
-Closed valves to reduce risk of a coolant leak when hot water was not needed
-There is a coolant leak somewhere between the engine and hot water tank or the tank itself so valves are closed

Aside from another point of failure in the coolant system sometimes a heating system can pull enough heat away from the engine that it doesn't reach operating temperature. You may need to bleed your coolant system after you open the valves and watch for a drop with the coolant level after you get the valves open and engine up to operating temperature. It shouldn't be to difficult to troubleshoot. Good luck.

 

[Marco Flamingo]

My PO had done something similar. The coolant system could shut off circulation to the water heater, to the Red Dot (bus heater), or adjust the circulation to both. Complex, but maybe necessary because he had drilled a hole in the thermostat. It is a hack used by hacks to supposedly help fill the coolant faster. Maybe. But as RedRascal posts, it can cause the engine to heat up slower. When I purchased, the engine wouldn't heat up over 130F when idling at the dock. Underway, it took 1/2 hour to get to a low operating temp (180F). It could be your valving is a "fix" for a mismatched thermostat.

 

[Jeff F]

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.

 

[Lepke]

My Detroits have a 1/2" line that bypasses the thermostat from the factory. It's to ensure there is always a small circulation of coolant. The engines don't seem to heat any slower than other engines. I doubt drilling a small hole in the thermostat effects the engine warming. Several new engines come with thermostats with a small hole and auto parts stores have them.
It's not a hack, it's a fix coming from the OEM that also works on other engines.

 

[tiltrider1]

If your water heater is downhill from your engines you could suffer from heat transfer from the water heater to the engines. Thus causing the water heater to work harder. If you plan to leave the water heater running through the winter but you know you won't be using the engines all winter, you might turn off the valves to slow down the heat transfer and save money. I find this one of those cases where the squeeze isn't worth the amount of juice you get. However, other are just bigger Penney pinchers than I am.

 

[psneeld]

I connected a buss heater, teed into my engine heated water heater via a heat exchanger.

I added 2 valves in the engine and water heater loop. They were put in in case of leaks or maintenance. Seemed like a normal thing to do.

OP's valves may be shut for either of the above reasons or the previous owner didn't like them open for running and just opened them when he couldn't heat his water with electric.

 

[Cigatoo]

Turn them on. Just be sure to run engine to temp and burp the air out of the cooling system. (May need to burp several times) As mentioned above plumbing in a $150 mixing valve set to around 120 degrees I’ll reduce any risk of getting burned. Without the mixing valve your hot water temp can get very very hot. May be why the PO had them shut off. Those look like Yanmar valves. Be aware that some of those valves may have BSP threads if you happen to try and replace.

 

[O C Diver]

I had a water heater and 3 bus heaters in a loop off the engine. With the bus heaters bypassed, it would take about 30 minutes to heat my 20 gallon water heater.

If running the water heater off the engine, the water heater gets up to engine temperature, scalding. There is a simple solution to this. Either a tempering or mixing valve will keep the water at sinks and showers from being too hot. I installed a mixing valve at the water heater. It takes the water heater hot water and mixes it with cold water. The valve is adjustable and can easily be set to a safe limit, mine was set to 125 degrees. My valve cost about $60.

On the OP's water heater, my guess is that the heater element may have failed (closed valves). That happened to a friend of mine. When the heat exchanger in the water heater failed, the domestic water pressure pushed the water through the heat exchanger, through the lines, through the engine, and out through the radiator cap. His solution was to close the valves to the water heater from the engine.

For the OP to test the heat exchanger, turn off and drain the pressure from the domestic water. With the engine valves to the water heater closed, remove one of the lines to the water heater heat exchanger. Them pressurize the domestic water. Usually leaks in heat exchanges are slow, so expect a small trickle of water.

Water heaters in houses don't last forever. They don't in boats either. Hopefully you get 10 to 15 years. As a result, if you plan to cruise and want really nice hot water, replace an old water heater and add a mixing valve. That's what I did.

Ted

 

[Bacchus]

It's not a hack, it's a fix coming from the OEM that also works on other engines.

I agree with Lepke and Yanmar is among the mfg that include a small hole in the OEM Tstats. Many boat mfg do not hook up the eng heating coil on installed water heaters, even though that feature is included. I assume that is a warranty / liability issue as there are many successful examples of the feature.
My WH has the coil but MS never connected it. I debated but finally decided that it's a good reason to run my Gen periodically, which I don't need / do otherwise.
Valves are a good idea in case a leak is detected they allow continued safe operation.

 

[Mambo42]

I have one heater like that as well and when I got the boat it did not have any valves. Was no problem until I had to change the heating element and after that needed to change the belt on my engine. Without valves on the water side you cannot drain the heater and without valves on the coolant side you will lose way too much coolant.
If your heater functions and you don't lose cooling liquid (or water) then your boiler works fine, I would not worry about opening up those valves. Just like others have already stated, you will need to add cooling liquid to the engine again, my boiler takes up about one gallon of cooling liquid. So without it your engine will most likely overheat.

And as others have stated, I love this boiler a lot. No need to use electricity to heat up water. If the engine has been running for about 2 hours the water in the boiler is hot and you can have a nice warm shower. On any next boat I will exchange any electric only boiler for a combination one like this, they are great.

 

[Bacchus]

The other important point I dont think has been mentioned is the need for CAUTION for all aboard when using hot water heated by tye engine as the temp is significantly hotter than w elec elements. An auto tempering valve is a good safety feature but EVERYONE ABOARD understanding the risk and need gor caution is necessary to avoid problems with unanticipated / sudden 180+ deg water

 

[Nick F]

The other important point I dont think has been mentioned is the need for CAUTION for all aboard when using hot water heated by tye engine as the temp is significantly hotter than w elec elements. An auto tempering valve is a good safety feature but EVERYONE ABOARD understanding the risk and need gor caution is necessary to avoid problems with unanticipated / sudden 180+ deg water

I disconnected the engine coolant from the water tank for exactly this reason - danger of scalding from water that is too hot. We also found that getting the water temperature right in the shower was very fiddly and wasted a lot of fresh water. We now only heat with electricity and the thermostat is set to be just right for the shower with no need to mix in cold water.

 

[DDW]

A good tempering valve will do the same thing, and give you a longer shower.

There is one additional hazard with this arrangement: if there is a leak in the coolant loop inside the water tank, and the domestic pressure ever falls below the engine coolant pressure, coolant will leak into the domestic water system. Normal ethylene glycol is highly toxic.

 

[Marco Flamingo]

There is one additional hazard with this arrangement: if there is a leak in the coolant loop inside the water tank, and the domestic pressure ever falls below the engine coolant pressure, coolant will leak into the domestic water system. Normal ethylene glycol is highly toxic.

Is there a food safe engine antifreeze? I recently flushed and replaced. I'd do it again if there's a safer coolant. My coolant circulating hot water heater appears to be original (1981). I've been keeping my eye on replacements. 6 gallon heaters are only about $400 on sale.

I replaced my Lehman thermostat with a Stant Superstat. They are no longer available new, but still show up NOS on Ebay, so I also bought a spare. It has a tiny scratch on closed valve to let air out, not a hole. Went with 194F thermostat to be closer to Lehman Operator's Manual recommendation. Have to be careful using hot water. No kids onboard.

 

[DDW]

Yes, Sierra and others make a propylene glycol based engine antifreeze which is non-toxic. I'd just make sure it meets the specs for your engine.

If you'd like a more recent water heater, I just removed an 11 gallon Seaward from my boat which would be a little newer than yours (2014 build). You are welcome to it for free, but would need to come fetch it in Anacortes. I am 1000 miles away. Might be up there early next year, but it is in a boatbuilders yard and I could arrange for you to pick it up.

 

[O C Diver]

There is one additional hazard with this arrangement: if there is a leak in the coolant loop inside the water tank, and the domestic pressure ever falls below the engine coolant pressure, coolant will leak into the domestic water system. Normal ethylene glycol is highly toxic.

While there is a risk of the above, most boats domestic water pressure is above 10 psi (30 to 45 PSI typically) and most engine radiator caps are below 10 psi. Long story short, my buddy's domestic water pressure pushed all the antifreeze through the radiator cap into the bilge.

Ted

 

[CaptTom]

Engine-heated water is the way to go. The first time I hooked that up on a boat it felt like such a luxury! I still feel that way.

On my current boat, I installed a solenoid valve on the upper coolant hose from the tank to the engine. It's only open when the engine is running. This solves the problem of heat loss from the tank when not using the engines.

I'd be wondering why the PO closed these valves and removed the handles. If the water heater is working normally on electric power, then I'd open them and see what happens.

Much as I love scalding hot water, especially at the galley sink, I caved in and installed a thermostatic tempering valve anyway. Not because I'm afraid anyone might be too stupid to understand how to operate a faucet and burn themselves. It's just that the hot water lasts a lot longer when it's mixed with some cold on the way out of the tank.

 

[DDW]

While there is a risk of the above, most boats domestic water pressure is above 10 psi (30 to 45 PSI typically) and most engine radiator caps are below 10 psi. Long story short, my buddy's domestic water pressure pushed all the antifreeze through the radiator cap into the bilge.

Ted

I had the same issue, however the domestic pressure is not always on (I turn the water pump off when I leave the boat for any long period, as I think most do), while the engine system is likely to have some pressure. It isn't a big risk, but antifreeze poisoning is supposed to be a very unpleasant way to die, so I mitigate that risk if I can.

 

[Jeff F]

I had the same issue, however the domestic pressure is not always on (I turn the water pump off when I leave the boat for any long period, as I think most do), while the engine system is likely to have some pressure. It isn't a big risk, but antifreeze poisoning is supposed to be a very unpleasant way to die, so I mitigate that risk if I can.

Doesn't most consumer antifreeze have bittering agent added? I've wondered whether that would provide a taste alert in case of antifreeze intrusion. I think it's mostly to prevent pet/wildlife poisoning.

 

[O C Diver]

I had the same issue, however the domestic pressure is not always on (I turn the water pump off when I leave the boat for any long period, as I think most do), while the engine system is likely to have some pressure. It isn't a big risk, but antifreeze poisoning is supposed to be a very unpleasant way to die, so I mitigate that risk if I can.

Does your domestic system hold pressure?

Mine has never been without pressure after months. If it were me, and I came back with the domestic system at 0 PSI, I might flush the water heater tank, but then I installed a check valve before the tee between the water heater and its expansion tank. So no contamination on the cold water side. I also don't drink hot water from the tap.

Could anyone post an article siting an instance of a failed water heater heat exchanger causing an antifreeze ingestion death?

My guess is that a boater is 1,000 times more likely to fall off the boat and drown than injest antifreeze from a water heater.

Now maybe I'm wrong and someone will post a fatality, but considering the likely hundreds of thousands of recreational and commercial boats with water heater heat exchangers over the last 75 years, I think this concept is pretty safe.

Ted

 

[DDW]

I agree with your characterization of the risk, but it is a ubiquitous warning on hydronic systems for the same reason. Also antifreeze has a very bitter taste mixed in to warn of contamination (pure ethylene glycol is sweet tasting). Apparently there are about 5000 cases on antifreeze poisoning a year in the US, probably few of those from domestic water contamination, but it is certainly plausible. The dosage required to need medical attention is pretty low, about 3 tablespoons for a child.

I am putting $700 of fuses in my boat to prevent probably even less risk, because the ABYC recommends it, and also run propylene glycol in the hydronic system. On the other hand I've done bungie jumping and hang gliding so not particularly risk averse.

 

[ancora]

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?

 

[heysteve]

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?

Yes, if the heating loop has a hole in it. But I would think you'd notice coolant when you turned on the hot water.

Edit: actually... I would think the higher pressure domestic hot water would overcome the lower pressure engine coolant supply. So maybe not. Still, if you're losing coolant into your tank you'd notice it when you turn the hot water on.

 

[O C Diver]

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?

Simple answer is close the valves on the heating loop. As mentioned, I would expect the coolant resevoir to be overflowing from the pressure.

It's more likely a leak in the heat exchanger to raw water.

Check your engine oil for discoloration.

Ted

 

[ancora]

Simple answer is close the valves on the heating loop. As mentioned, I would expect the coolant resevoir to be overflowing from the pressure.

It's more likely a leak in the heat exchanger to raw water.

Check your engine oil for discoloration.

Ted

That's what I'm afraid of, a bad heat exchanger, I'm just grasping at straws.

 

[Jeff F]

Also antifreeze has a very bitter taste mixed in to warn of contamination (pure ethylene glycol is sweet tasting). Apparently there are about 5000 cases on antifreeze poisoning a year in the US, probably few of those from domestic water contamination, but it is certainly plausible.

Ethylene glycol maybe. I suspect few from the bitter antifreeze.

I know it would be diluted in the FW system, just wonder how much the bitter would warn before health consequences. My vague understanding is that it's the most offensive taste available/practical.

I don't fret what's in the engine, assuming protection from a number of angles as mentioned above.

But I understand the zero risk approach. JD offers polypropylene glycol antifreeze. Apparently it's commonly used in food handling applications. Why not use it?

 

[DDW]

There are many commercially available PPG antifreezes made specifically for hydronic systems. There are a few made specifically for engines. They are pretty widely distributed and easy to find.

 

[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?

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.

 

[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.

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?