Engine Connections to Hot Water Tank

[Reteves]

Quick question to the forum. We installed a new Raritan 6 gallon hot water heater and although the tech who has the instructions was inquiring about which engine hoses need to be connected to which tank connection. The engine connections have ben upgraded with shut offs, but does it make a difference which one goes to the tank and which one returns? It's a loop, the hot engine coolant goes out and then comes back. Period. Thanks in advance for your responses. First boat with one of these newfangled devices.

[GordMay]

Greetings and welcome aboard the CF, Reteves.

Typically, engine coolant enters (from the engine) the HWT exchanger at the Top, and returns (to the engine) out the bottom; BUT confirm with your Hot Water Tank manufacturer’s instructions.
➥ http://www.raritaneng.com/pdf_files/.../L206v0911.pdf

[David M]

There should be a flow indicator or labeling on the hot water tank itself. If not, do as Gord recommends and call the manufacturer or read the instructions.

[Reteves]

Thanks all. Consulted the Service Manual on the Yanmar. It distinguishes an inlet and outlet!

[Steve O]

Do you have a bypass fitting on the engine hoses? Typically your hose on the engine is 1.25 or 1.5 inch and the fittings on the water pump are 0.75 or 1 inch. You cannot get enough flow of coolant through the hot water tank in order to prevent the engine from overheating. You need some to be diverted back to the engine without going through the hot water tank.

[s/v Jedi]

We have connected it to our genset. For this we used the coolant drain as the point where coolant returns to the engine. We opened an already tapped port near the pump for the 2nd hose. The pressure is higher there and this creates more than enough flow in parallel to the heat exchanger flow.

The official method is to add a heat exchanger in series with the coolant-raw water heat exchanger. That extra heat exchanger is then made part of a loop that includes such extra heat exchangers at engine and genset, plus the water heater, hydronic heater and a loop through the boat interior like standard hydronic heating.

[sailor0516]

Is there a way to make hot water while at anchor, idling 1000-1200 rpm.
I have hot water heater with heat exchanger but mfg rep says must run engine under load for 45 min. Hate pull anchor just for that. New boat to me so not sure if hot water heater at fault. It does work on shore power.
Thanks in advance.
sailor0516

[Blue Stocking]

Load or no load, engine should get 180-200 * F as normal operating temp. May take longer with no load (idling), ergo, load comment.

[belizesailor]

Originally Posted by Reteves

....the tech who has the instructions was inquiring about which engine hoses need to be connected to which tank connection...

Doesn't sound like he's worth of that moniker...hope his rate was low and he didnt screw anything up!

[sailor0516]

The engine does reach normal operating temperature 180 F while idling, may be the water heater itself. Thanks for the help.
sailor0516

[Jd1]

Diesel engines need a load to be happy. Do not run a diesel at idle for extended periods of time.

[JK n Smitty]

Originally Posted by Jd1

Diesel engines need a load to be happy. Do not run a diesel at idle for extended periods of time.

Ok, not to sound like a jerk but do you have anything to support that statement?

I have always been of that opinion but never had anything to support it. Just read it on the intranets. On another forum I made this statement and was surprised to be corrected on it by some pretty knowledgable boat people. I am still researching it but I am now leaning to the idling a diesel does little to no damage. Diesel trucks and earthmoving equipment idle for large portions of their life. Many cruisers use the diesel in idle to charge batteries and heat water and they have thousands of hours on the engine with no issues.

Just some thoughts

Fair winds

Jesse

[Dulcesuenos]

Our port motor is the one plumbed into the water heater. There is a "flapper valve" in line not 100% sure but i can tell you the water pump will not push this open unless its under load or higher rpm I am thinking the reasoning is if you had an extra 2-3 gal of coolant circulating all the time even at idle the coolant would never properly heat up and engine issues such as carbon buildup , fouling etc could occur. My engine needs at least 1700+ rpm to force open the flapper to redirect hot coolant to the heater. Hope this helps. Its ok to idle diesels, ours idle at 1300 anyways. Doubt its going to ever be an issue as long as you run a thermostat and the engine operates at temp, doesnt really matter for us as it wont heat water at that rpm. . Though its good to blow them out once in a while if you lots of idling.

[Jd1]

Originally Posted by JK n Smitty

Ok, not to sound like a jerk but do you have anything to support that statement?

Absolutely nothing other than experience and a lot of stuff I read at various times (not able to quote though which stuff)

Everything I have read and have experienced supports the notion that a diesel is best run in the 75% to 90% (or thereabouts) power output range. An occasional period of idling will not be detrimental if followed by a period of running at a good load (for example starting the engine and letting it idle for a while to warm up before heading out). The frequent in and out of the harbour short hops are murder to the poor diesel.
I can not explain why automotive diesels, which spend a lot of time idling, survive. I could speculate though that they would last a lot longer if run like a semi trailer road transport truck - much harder and much longer.
A modern diesel should last 20000 to 30000 hours yet they get replaced in boats at a fraction of the expected service life. IMHO that is, amongst other things, related to the unfavourable working conditions of a sail boat auxiliary engine.
Diesels like to run fairly hot (180 - 190 F range). Running colder and/or idling a lot causes more wear and tear, carbon buildup and soot buildup.

I am sorry that I can't produce a link to something official looking.

[nes]

I don't know if this applies to the small diesels (non turbo/super charged), but the diesel generator that I have a lot of experience running had 36 cylinders displacing 645 cubic inches each, and it had an interesting gear driven (at low load) turbo (at full load) charger/compressor.
This diesel had very specific directions against running at low load (less than 30%).
The reason given for the load restriction was lower cylinder pressure at low load. The piston rings are designed to operate at rated load combustion pressures, this ensures normal lube oil consumption rates. Light and no load operation promotes “souping”, which is excessive oil escaping past piston rings into combustion chamber. Souping causes smoking exhaust and potential exhaust manifold fires.

The recovery direction, if the engine was run at low load, was to follow that with at least a half hour at greater than 50% load.

Based on what I have seen running this engine, I would suggest that it is not a good idea to do extended runs at low load.