Too long to get hot water for shower

[Tonick]

Hi Folks. I have a problem with my Volvo 2003, when I run it in navigation, I can get hot water for the shower in 15 minutes, but when anchored, I start the engine take it to 1.500rpm, and after one hour, I still don´t have hot water for shower. Is this normal?, thank you.

[irwinsailor]

It is my understanding that a diesel engine does not generate much heat unless it is under load.

[Captain Bill]

If your heat exchanger is on the fresh water cooling side (which I bet it is) the issue is that the waterpump on the diesel will not generate sufficient flow in the auxillary loop at such low RPM. I have a hydronics heater on my Yanmar 3JH3CE and it works great at crusing RPM (2500-2900) but doesn't put out any heat at 1500. This is despite the engine temperature being in the normal operating range. This is especially a problem if the tank is higher than the engine. A circulating pump can solve the problem.

[Tonick]

Ok, I´ll try to increase the rpm, but my Volvo cruise rpm is 2.000 rpm, i think i shouldn´t pass it. And what do you think about change the termostate of 60 degrees for a higher one?. Thank you four your reply.

[Captain Bill]

I have 60 degree thermostats on my engines and the water gets quite hot. 60 is the maximum recommended thermostat for the Yanmars, with 50 degrees being standard. I don't know what the maximum is on Volvos. If the RPM is insufficient then a higher thermostat won't help. All that hotter water will just stay in the engine. I don't know what access you have to the hoses on the auxillary coolant loop, but on my engines only abut the first foot of the hose gets warm when running at low RPM, but when I hit the threshold for circulation the outgoing tube becomes quite hot. If your outgoing hose is not hot to the touch you are not circulating. Just keep increasing your RPM until the hose gets hot. I'm not a diesel mechanic, but my understanding is that it's better if you can load the engine if your going to run it for any significant length of time.

[Tonick]

Ok. i´ll test it increasing the rpm, thank you very much four your replies.

[Amgine]

Load is not the same as rpm. Try putting it into reverse (so the engine is actually working, but not going to trip your anchor.)

[James S]

I'm a bit baffled by all this...it just seems that if the engine is up to temp...then that’s the temp!!

Have you checked to see if you have an air lock in the exchanger coil in you water heater?

Is it by chance higher than your engine?

I'm not sure how this would explain it working when you’re actually underway?

I’m betting on a vapor lock!

[Sandero]

This has little or nothing to do with RPM. FEEL your engine. If it is not hot to the touch, don't expect much in the way of hot water made for the heat exchanger.

In the summer, my engine is always pretty warm and heats up faster and gets too hot to touch. Hot water is no problem. In the winter with cooler seawater and colder air temps the engine doesn't run as hot as quickly. How long do you expect to run the engine to heat up say... 6 gallons of very cold water with a "heat exchanger".

So you have several factors to consider:

Ambient air temps
seawater temps
temp of tank water to start
volume of tank water to heat

Assuming your engine is not over heating or running too cold...

I think you'll find that in cold weather it justs takes longer.

[James S]

Whats your engines temp gauge say?

[svHyLyte]

No engine load=no heat (and ruins an egine in short order). Try Solar Shower 5 Gallon (18.9 Liters) . This will heat 70 deg water to 108 deg in 3 hours, even on a cool day. We keep one on the foredeck when we're on the hook and hoist it over the hatch above the lavatory with a halyard when needed. The tube drops right into the shower stall.

FWIW...

s/v HyLyte

[Randall]

your engine will keep a constant temp at a certain rpm but that dose not mean the water going thru it will become hotter the water becomes hotter as the heat is transfered to the water to keep the engine at a constant temp. So if th engine dose not need to cool down only so much heat will transfer to the water. At idle speed i can put my hand in the out take flow so if that water is not hot, your shower water will not be hot.

[Sandero]

Let's talk why and engine is "hot". My uneducated understanding is that internal combustion engines produce explosions of hot gas in their cylinders. My sense is that all those explosions are about the same temperature and that the heat needs to be removed because the moving metal parts will heat up and expand and sieze up. Oil lubricates and it has to work in a very hot environment. The cooling system in these engines is meant to remove excess heat. More explosions, more RPMS more heat to remove. But I don't think an engine will run cool to the touch.

A heavy engine has a lot of thermal mass / inertia so it take a while to heat up and to cool down. When the engine reaches normal operating temperature the thermostat will a"open" and allow water to circulate to remove the heat - the cooling system. This heat heats up the coolant which passes it's heat to the another air via a radiator in an auto or to seawater on a boat (assuming it is fresh water cooled).

You simply can't keep having "explosions" of hot gases and not have to remove heat which can then exchanged to heat hot water.

[never monday]

Originally Posted by Tonick

Ok, I´ll try to increase the rpm, but my Volvo cruise rpm is 2.000 rpm, i think i shouldn´t pass it. And what do you think about change the termostate of 60 degrees for a higher one?. Thank you four your reply.

First
Most of the 2003's out there are raw water cooled. I am going to assume your is one of them.

Second,
DO NOT change the thermostat. Salt comes out of solution in the mid 150* F. 60*C was specified by Volvo to minimize this happening.

Now,
if you want to a) make the engine live a long and healthy life. And b) want hot water for a shower. Then start the engine, when the oil pressure stabilizes engage reverse and pull on the anchor at a speed above idle. Somewhere around 1200-1500 should provide the desired result. Go too fast and the volume of the raw water pump increases and cools thing off.

Also,
I understand you never run your engine above 2000 RPM? That engine is rated for continuous duty at 3200 RPM. You must be able to acheive this underway at full throttle. If not prop adjustments should be made.

[Morgan 27]

My boat didn't come with a hot water system so I got one of these. You can plumb the heater part in super easy and have hot water on the hook without all the engine fuss. Or leave it in stand alone mode. I use mine to wash the deck when it's cold out...
My $1.295






Zodi On Demand Hot Water & Portable Hot Showers