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Old 03-07-2016, 06:42 AM   #21
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One problem you may run into is that the heater system may cool the engine system more than normal. The thermostat bypass is designed to keep the coolant at a minimum temp and still circulate coolant to avoid hotspots, and with cold water into the heat xchanger it may be at the minimum. Add in another cooling source, at idle, and your engine may be running very cold. Newer electronic engines especially don't deal well with this.
This is true, though in practice it doesn't seem to be much of an issue. The only time I have seen a noticeable engine temp drop was this past summer in Alaska. Water temps were in the 40's, air temp was in the low 40's, heat was running throughout the whole boat (and keeping up without any issue), and we were idling for a long time while picking though ice. Other than being in the arctic, I think these were about the worst case conditions. Our normal idle temp is 160F, and as I recall it dropped a couple of degrees below that, but only a couple. With any RPM above idle, it came right back up. My assumption has always been that the size of the diversion ports are small enough to prevent over cooling of the engine.
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Old 03-07-2016, 06:51 PM   #22
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Install petcocks at the engine where you connect so you can shut it off if you need to or if you don't need the heat.
Great idea. I need to do this on the other engine that provides heating for the water heater.
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Old 03-07-2016, 10:31 PM   #23
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This is true, though in practice it doesn't seem to be much of an issue. The only time I have seen a noticeable engine temp drop was this past summer in Alaska. Water temps were in the 40's, air temp was in the low 40's, heat was running throughout the whole boat (and keeping up without any issue), and we were idling for a long time while picking though ice. Other than being in the arctic, I think these were about the worst case conditions. Our normal idle temp is 160F, and as I recall it dropped a couple of degrees below that, but only a couple. With any RPM above idle, it came right back up. My assumption has always been that the size of the diversion ports are small enough to prevent over cooling of the engine.

I would agree with this. Cars and trucks idle for hours (I5) in the Puget Sound and the operating temps do not vary but a few degrees.
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Old 03-08-2016, 07:05 AM   #24
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An ideling car or truck will see return water that is barely cooled enough to keep the engine from overheating.

Usually about 20deg F lower than when pumped to the radiator.

A keel cooler (without a by pass thermostat) can return coolant close to the surface water temperature.

160 F -180F out 50F return , no problem with a bypass thermostat . in the coolant , big problem if only relying on the engines stock internal unit.
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Old 03-08-2016, 07:34 AM   #25
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What you want is often called a bus heater. Heatercraft, among others makes the exchanger/blower unit. You use the same engine taps that supply coolant to your boat's hot water heater, if installed. You typically plumb the water heater first and then the coolant flow goes to the bus heater and then back to the engine.


There are some hydraulic tricks about elevation and venting that need to be observed.


You also need to know that heat will stop fairly soon after you shut the engine down.


David

That's what I did and my only question was, why did I take so long to do it.
Heatercraft about $280
great deal and works so well.
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Old 03-08-2016, 10:38 AM   #26
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I would think that if you had the heater in the same loop as the water heater, and assuming it (water heater) is also a.c. powered, with the gen running it would help keep the coolant temp up. Just an observation, no practical experience as I havent boated anywhere that I needed cabin heat.
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Old 03-09-2016, 07:53 AM   #27
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"You also need to know that heat will stop fairly soon after you shut the engine down."

In both our bus conversion and on LUCY we have a small circ pump in the box heater circuit.

For mild weather a 3,000 lb hot diesel will give enough heat to make it comfortable for a few hiurs after engine shutdown.

It does cost batt amps as the heater fan even at slow is a hog , but is nice and quiet .
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Old 03-09-2016, 08:09 AM   #28
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Trouble with trying to use the hot water heater as a source for a bus heater...there is a double transfer loss (engine to water heater and then water to air at the bus heater, plus piping losses).


The water heater element is typically only 1500 watts (about the same as a space heater) but you lose at the transfer from piping to airflow thru the bus heater. So after the initial hot water is used up...you are trying to heat with a 1500 watt element inefficiently.


You would be better off with space heaters loading up the genset or piping a setup where the genset provided coolant heat transfer to the bus heater circuit or just a separate bus heater.


Unless you get fancy like FF suggests and keep engine coolant circulating after the engine is shut down.
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Old 03-10-2016, 07:31 AM   #29
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"Trouble with trying to use the hot water heater as a source for a bus heater."

We use the 3000lb iron mass of the 6-71 as the heat source , not the puny 10G in a hot water box.

Nothing fancy , just a tiny 12V centrifugal pump.
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Old 03-10-2016, 07:56 AM   #30
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FF, please advise the (circulating) pump details that you are using...and is it in the engine water circuit while the engine is running ? or valved off ?
and last question....does it push the water in the same direction as the engine pump (when the engine is running). thanks in advance for the info
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Old 03-10-2016, 11:21 AM   #31
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One problem you may run into is that the heater system may cool the engine system more than normal.
To avoid over-cooling from auxiliary heater systems, Cummins supplies a restricted hose fitting, PN 3916256. Here is a link to the Cummins B and C Series engine installation (2015) courtesy of Seaboard Marine. Go to page 35 for Auxiliary Heating Circuits.

http://www.sbmar.com/wp-content/uplo...Directions.pdf

I'm preparing a 6B5.9M that will be going in my boat next month, and I am using that fitting. I thought about using a regular NPT/hose barb fitting and an inline valve to control the flow, but the Cummins part just makes it simple.
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Old 03-10-2016, 01:10 PM   #32
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I forgot to mention, my local Cummins Parts Department had it in stock and it was under $12.
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Old 03-11-2016, 07:17 AM   #33
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and is it in the engine water circuit while the engine is running ? or valved off ?
and last question....does it push the water in the same direction as the engine pump (when the engine is running). thanks in advance for the info

OTS small Groco bronze centrifugal pump.

Not on while engine is operating , but I guess if it got cold enough underway it might help.

Pumps in same direction as engine coolant pump, From hot wet exhaust manifold back to block.
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Old 03-11-2016, 08:35 AM   #34
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My engine cooling system has a short loop to a heat exchanger inline with my hydronic system. I originally thought I'd heat the engine in winter AND be able to scavenge heat from the engine for cabin heat (which also heats the domestic water heater) but without a booster pump in the engine circuit I couldn't heat the engine when it wasn't running. And I've never gotten around to installing a hydronic circulation pump switch for scavenging. And trying to figure out whether I'm putting heat into or extracting heat from the cooling system when both are running makes my head hurt, so I've left the exchanger closed off.
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Old 03-11-2016, 12:12 PM   #35
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I'm not 100% up on the nomenclature, but when I bought a "tempering valve" years ago for my house, it just passed a set amount of cold water, regardless of the relative temperature of hot and cold:


I ended up ripping it out and replacing it with a "thermostatic mixing valve":


I think the latter is what FF is referring to.

The tempering valve can only statically adjust the amount of cold water by turning the dial on the top. And even that didn't offer enough range for the wide swings of both the incoming cold water (seasonal) and the domestic hot water (from the boiler.)

I suspect it's the same in a boat, so I put in a proper termostatic mixing valve.

In my case, it wasn't so much about scalding - most people are smart enough not to hold their hands under steaming hot water that long - but to get a more even temperature and extend the time between having to power the water heater.
Both of the valves you show should work fine, functionally the same. Maybe you had a bad one. Both are tempering /anti-scald valves. The upper one, made by Watts, needs it's guts removed b/4 any soldering is done or it is ruined.
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Old 03-11-2016, 07:07 PM   #36
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All you guys with a circulation pump installed. How long was the hose run? I am looking at about 10 feet. The heater will be in the same area as the water heater and I doesn't have a pump on it.
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