Yanmar 2GM diesel...hot water heater?

[RichH]

To get the best amount of heat into a water heater on a raw water cooled engine is to break into the raw cooling line between the exhaust manifold and the water injection elbow. Doing so will intercept the hotter water effluent from the exhaust manifold, hotter than the main engine raw cooling circuit ... which should only be operating at about 155°F max.

The problem with a raw water cooled engine is that it will bypass its cooling water until the thermostat closes when the 'block' is full up to that 155°. Therefore to heat water, you really have to 'run hell out of the engine' before you can expect any hot water from the 'water heater'.

 

[Blitz]

To get the best amount of heat into a water heater on a raw water cooled engine is to break into the raw cooling line between the exhaust manifold and the water injection elbow. Doing so will intercept the hotter water effluent from the exhaust manifold, hotter than the main engine raw cooling circuit ... which should only be operating at about 155°F max.

That's what I suggested earlier in this thread and has worked for 30 years on my boat. Quite easy, no tees, no drilling, etc.

 

[kloudie1]

True, but that line is not available on the 2GM engine. The elbow bolts directly to the head and the water going to the ell is tempered with the thermostat bypass water, so that water is quite cool.

 

[Blitz]

True, but that line is not available on the 2GM engine. The elbow bolts directly to the head and the water going to the ell is tempered with the thermostat bypass water, so that water is quite cool.

Sorry, you are correct. The 2GM is a different animal all together now that I got my book from the boat and looked at the schematics.

 

[AirborneSF]

I hear a 'story' that a guy installed a car heater in his boat by putting the heater inline between the eng. outlet and the 'mixing elbow'. Never heard if it worked, but I'm guessing it would, if the eng gets to 180 deg.

 

[Ron20324]

I hear a 'story' that a guy installed a car heater in his boat by putting the heater inline between the eng. outlet and the 'mixing elbow'. Never heard if it worked, but I'm guessing it would, if the eng gets to 180 deg.

Not so far-fetched. In the army in Germany we had a jeep (gas engine) for runs all over the country. Canvas doors only, it sure got cold. We got a heater for a 2.5 ton (deuce an' half), installed it between the jeep front seats, and it worked great- no ducting needed, just B&G and engine feed/return hoses. To boot, in the plenum chamber we could heat our food. I'd love to have that simple heater for the boat.

 

[Hubbmeister]

I have a 31 and replaced the water heater with a Eccotemp tankless propane water heater designed for camping. cost about $120. The original was fed by heat exchanger.

 

[bugbitten]

Just an update on this project. I have the engine mostly back together (there's a mixing elbow issue I'll start a separate thread on) with proper marine heater hose running from the FWP to the water heater. All seems to be functioning as intended, although the engine started at 47° and the water temp in the James River was 52°, so tied to the dock I was just able to get the water in the tank up to warmish. I had a temporary section of transparent hose in the water heater loop so I could see when all the air was out of the system. I was very pleased to see how much more water I was seeing come out the exhaust, compared to the old, restricted mixing elbow's output.

Thanks to all for their help and support.

John

 

[azambella]

Been here, done this.

Sorry to say, If you have tru, un-modified 2GM, you can run it all day at full throttle and it will
barely get warm to the touch. It can't make hot water, I made many inquiries on doing so with no success.
The other factor in this equation is the thermostat temp on a 2GM temp is set low to keep salt water from
scaling up in the engine and exhaust. So, Changing the thermostat to a higher temp will subtract some years
from your motor (if your in salt water).

Best plan for hot water off the dock is fuel fired. I did the propane set up like in the archives on
this site. very happy with it. Low cost, easy to do. no shortage of hot water, no-tank.

Z

 

[bugbitten]

I've actually been getting plenty of hot water from my 2GM, to the point where, as the Woodster warned, I've been tempted to put in an automatic mixing valve to keep people from scalding themselves. I checked it recently, after a winter's day's sail where the ambient temp was upper forties and the river was a few degrees lower (I do keep the cabin heated, but the area of the hot water tank and the tank itself was probably no more than 55°). It brought the tank to 130 degrees after maybe 40 minutes of intermittent running. The engine itself gets to maybe 150° F or so.

John

 

[Charles Erwin]

Hi, I have a Yanmar 2GM diesel .. .A friend of mine has . . . the same engine. . . except his engine looks a little different and has some type of heat exchanger on it.

Your motor is different from your friend. Yours has direct sea water cooling and is designated 2GM C (possibly 2GM20 C.) The thermostat opens at 107F and is full open at 125F. If the seawater is cool the thermostat will never be fully open.

If you ran the motor in seawater at 150F salts will precipitate out of solution fouling the the motor cooling passages as well as the water heater heat coil. And - even if you could get this 2GM to make seawater hot enough to do anything, no one builds a water heater that tolerates seawater through the heat transfer coil.

Charles