Yanmar 2GM diesel...hot water heater?

rufus1138 · Nov 3, 2014

Skippie10 said:
Hi, I have a Yanmar 2GM diesel in my S2 Sailboat and when my electric hot water heater rusted out, I replaced it with a Sigma and the new water heater has "inlet and outlet" locations for "engine" heat. I'm presuming that these connections allow a person to use the engine heat for hot water but I don't know where to hook into my Yanmar diesel to provide the connection.

A friend of mine has a 28' pearson with the same engine....except his engine looks a little different and has some type of heat exchanger on it and he does have "engine hot water heat" when his engine is running (which I do not have).

So, what's involved in getting heat from my engine into my hot water heater? Do I need a special heat exchanger like my friend has and if so, any idea as to cost? Maybe it's not worth the hassle!

Don

don't need a heat exchanger, my raw water cooled 2gm is plumbed into my domestic tank as a heater all it takes is a tee fitting anywhere after the water pump and another before the mixing elbow, many many ways to do it, find a good fit for your boat, someone with an s2 should be able to help better.

woodster · Nov 3, 2014

if raw water cooled engine i don't think you are going to get good hot water by running the engine water through the hot water tank ...all i have read is that it takes an engine with a heat ex changer to do this but i could be wrong as it is my interpretation of all i have read

rufus1138 · Nov 3, 2014

mine comes out hotter than you want it to after motoring for anything more than 15 minutes lol, the heater in my water tank from the motor is very very efficient or something, its only a 5 gal tank or so but it gets hot, almost dangerously so, definitely equal to the operating temp of the engine, I think mine is tapped right at the output of the block cooling loop and then runs to the domestic tank and back to the mixing elbow.

Ron20324 · Nov 3, 2014

Heat exchanger has nothing to do with heating the water from the tank. It's purpose is to COOL the engine's coolant. So, does your friend have two hoses that go off of the engine, then to the water heater? One of them MIGHT come off the thermostat housing. Don't you have the engine manual?

spraygun · Nov 3, 2014

Here is a pic of the two brass pipes that are sticking up.Those are the locations you can use to plumb to your heater.This is on my 3gm.But the 2gm is the same.You will need to add much more coolant than normal.

kloudie1 · Nov 3, 2014

If it is a raw water cooled 2GM, the problem is that you can't get to the hot, thermostat temperature controlled water without some work. If you tee into the existing external hoses, you'll get tempered water that will be a blend of the hot water from the block and head, and the cold water that bypasses the thermostat. (The older QM models have access to the block water before mixing with seawater) Spraygun's picture is of a GM F which has a heat exchanger and is set up for a water heater, not like the seawater cooled GM. To get hot water for the heater, I think you'd have to drill/tap a hole into the thermostat housing and take water there and return it by teeing into the water hose going to the mixing elbow.

kloudie1 · Nov 3, 2014

2GM Cooling

OK, here is a diagram of the raw water cooling system on a 2GM. Note that the cold water leaves the pump and goes to a tee. Water goes to the block and goes to the top of the thermostat housing. When the engine is cold, the thermostat is closed and most water bypasses the block.. at that point, all external hoses will have cold water in them. As the block heats, the thermostat will open and begin to allow hot water from the block to pass and mix with the cool bypass water in the thermostat cover. The water from the thermostat cover to the mixing elbow will be warm but not hot.. it will produce tepid water but not nearly hot.. To get hot water ya need to get an outlet on the thermostat housing, between the thermostat and the block.. the water there will not have been mixed with cold and it will have a higher pressure than water on the mixing elbow side of the thermostat. That is the water that should be used to heat the water heater. You may be able to tee into the alarm switch hole, but to get good flow, you'd most likely have to drill and tap a hole in the thermostat housing and install a nipple. From there to the heater, then back from the heater to the hose going to the mixing elbow.. That will provide enough heat to heat water in the heater.

Use automotive or marine "Heater Hose" for those water lines..

Allan12210 · Nov 3, 2014

Don,

Looking at that thermostat and cover with its offset inlet and outlet reminds me of how a valve works. That nubbin on the thermostat makes me believe it (the thermostat) has a dual function of opening when heated sufficiently allowing water to circulate from the block while at the same time closing the path of cold water passing over the thermostat cover. After all, with two paths what's to stop the water from just taking the cold water route preferentially and the engine just overheats and boils? And why divide the water from the pump anyway? If it interrupts the cold flow as I think, then go from the thermostat cover outlet to the water heater inlet, then from the water heater outlet back to the mixing elbow because the thermostat cover isn't a mixing chamber, its a switch....first full cold then full hot at the exit.

I hope no one read my original post about adding Tee's and capping one side of the thermostat housing. Of course, if this doesn't work, then I'll post an alternative proposal.

Good luck.

Allan

Blitz · Nov 4, 2014

I have a 3GM raw water cooled. My boat has always been setup to allow the raw water cooling circuit to heat my hot water heater. In my case it is a Raritan Hot water heater. Although it won't get scalding it does heat it up quickly in my opinion.

There are no need for tees and a tee won't necessarily work well since that would only direct some of the cooling raw water to your water heater.

My hose from the thermostat housing goes to the front of the exhaust manifold cooling jacket (on top). On the rear end of the cooling jacket the hose that normally would come out and go to your exhaust mixing elbow would go to your water heater. And then from your water heater back to your exhaust mixing elbow . (BTW: My return line to the exhaust elbow has a vented loop in it) With this configuration you start heating your water heater even before your thermostat opens.

Let me know if you need any further clarifications.

I think this was covered in earlier posts years ago as well.

pateco · Nov 4, 2014

I have a raw water cooled 2GM that is plumbed for hot water. I have not tested it since we purchased the boat a couple of months ago. Testing the heater for both engine heat, and electric heat is on my to do list, but has taken a back seat to other projects. The next time I am on the boat I will take pictures of how it is plumbed.

Allan12210 · Nov 4, 2014

Allan12210 said:
Don,

Looking at that thermostat and cover with its offset inlet and outlet reminds me of how a valve works. That nubbin on the thermostat makes me believe it (the thermostat) has a dual function of opening when heated sufficiently allowing water to circulate from the block while at the same time closing the path of cold water passing over the thermostat cover. After all, with two paths what's to stop the water from just taking the cold water route preferentially and the engine just overheats and boils? And why divide the water from the pump anyway? If it interrupts the cold flow as I think, then go from the thermostat cover outlet to the water heater inlet, then from the water heater outlet back to the mixing elbow because the thermostat cover isn't a mixing chamber, its a switch....first full cold then full hot at the exit.

I hope no one read my original post about adding Tee's and capping one side of the thermostat housing. Of course, if this doesn't work, then I'll post an alternative proposal.

Good luck.

Allan

After a conversation with Kloudie1 (thanks Claude) I now understand better the function of the thermostat housing. It appears that the thermostat does throttle the flow of hot water and cold water together, so there is mixing in the cover. This will result in tepid water flowing to the mixing elbow (or water heater if plumbed from there). Doesn't seem to have the capacity to heat much. If an external thermostat can be used, or some way to space the existing thermostat out allowing for a tap off the block then reintroducing back at the thermostat, there might be a better result.

Grouperhound · Nov 4, 2014

This may sound crazy but could you put a 'Tee' into the Temp Sensor port, accommodating both the sensor and a feed to the water heater? The return would be another 'Tee' between the thermostat and the mixing elbow. One issue with any of these ideas of tapping the engine and bypassing the thermostat is that it will take longer for the engine to come to proper operating temperature. Might not be a problem on a larger engine but the 2GM is kind of petite in terms of heat output.

spraygun · Nov 5, 2014

Not sure if this helps.This is my 2gm.Although it has a heat exchanger.you can pretty much tap in lots of places. I don't use this engine to produce heat because I get get that from my other Yanmar.I realize that there may be differences in the thermostat housing on a raw water cooled.My 2gm and 3gm have same water pump and thermo housings.The pictures are just for reference.Trying to be helpful.

spraygun · Nov 5, 2014

Here is where I get hot water from on my 3gm.

pateco · Nov 23, 2014

Here is my 2GM attached to water heater hoses.

Coming from Engine bay to under galley sink:

Attached to hot water heater:

Back out to Mixing Elbow:

I hope this helps.

kloudie1 · Nov 23, 2014

Pateco, That source is the tempered water from the block after it has been mixed with cold water, coming in from the bottom hose on the thermostat cover. . I doubt that water would be much above 100F .. The heater will be fine on electric power, but probably not so using engine heat.. Exactly what I was talking about.. If you want hot water from the engine, you'll have to connect either by teeing into the thermostat switch or drilling and tapping into the thermostat housing, just aft of the top hose. That would go to the heater then back and tee into the hose leaving the thermostat cover on top and heading to the exhaust ell.
Side note; I didn't realize that some 31's were supplied with raw water cooled engines.

pateco · Nov 24, 2014

kloudie1 said:
Pateco, That source is the tempered water from the block after it has been mixed with cold water, coming in from the bottom hose on the thermostat cover. . I doubt that water would be much above 100F .. The heater will be fine on electric power, but probably not so using engine heat.. Exactly what I was talking about.. If you want hot water from the engine, you'll have to connect either by teeing into the thermostat switch or drilling and tapping into the thermostat housing, just aft of the top hose. That would go to the heater then back and tee into the hose leaving the thermostat cover on top and heading to the exhaust ell.
Side note; I didn't realize that some 31's were supplied with raw water cooled engines.

I tried it out yesterday. Ran the engine at about 1500 RPM for 20 minutes. No hot water at all. Any pictures on how to improve this would be greatly appreciated.

This is an early31 from 1983

Yanmar 2GM diesel...hot water heater?

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