I have a 2QM15 that is raw water cooled.

In looking at cooling water circuit, it flows like this:

- Water from CW pump flows to splitter - part goes into block and part flows
to thermostat housing mounted on top of exhaust manifold where it mixes with
hot water exiting manifold and then flows to exhaust pipe mixing tee.
- Water that enters block, flows through block and cylinderhead and then
exits at top of head and flows to front of exhaust manifold via a rubber
hose.

Presumably, there is always a flow to the exhaust elbow, but when the
thermostat opens, hot water exiting the manifold mixes with the cold water
before flowing to the exhaust.

The mixed water entering the exhaust pipe tee would presumably be too cool
for heating water in the water heater.
Question is, is there another place I could tap into hot water before
mixing?

In looking at diagram, it looks like one way, would be to pipe the water
leaving the cylinder head though the water heater before sending it to the
exhaust manifold. Initially. while bringing water tank up to temperature,
this would cool the water before it enters the manifold jacket, which would
cause the thermostat to stay closed for longer. But, once the water in the
tank is hot, it would work normally.

Can anyone see anything wrong with this? One good thing, is that the over
temperature sensor would warn if the engine gets too hot (because the
thermostat has not opened).

GBM

Better to simply 'tap into' the exhaust header outlet hose and 'branch'
into the hot water heater then back to the injection nozzle.

The circuit is a direct connect between the block and the exhaust
manifold on the Q series Yanmars ... so this may be difficult to do as
you propose. Besides, the water will be much hotter coming off the
exhaust manifold.

In article , GBM
wrote:

I have a 2QM15 that is raw water cooled.

In looking at cooling water circuit, it flows like this:

- Water from CW pump flows to splitter - part goes into block and part flows
to thermostat housing mounted on top of exhaust manifold where it mixes with
hot water exiting manifold and then flows to exhaust pipe mixing tee.
- Water that enters block, flows through block and cylinderhead and then
exits at top of head and flows to front of exhaust manifold via a rubber
hose.

Presumably, there is always a flow to the exhaust elbow, but when the
thermostat opens, hot water exiting the manifold mixes with the cold water
before flowing to the exhaust.

The mixed water entering the exhaust pipe tee would presumably be too cool
for heating water in the water heater.
Question is, is there another place I could tap into hot water before
mixing?

In looking at diagram, it looks like one way, would be to pipe the water
leaving the cylinder head though the water heater before sending it to the
exhaust manifold. Initially. while bringing water tank up to temperature,
this would cool the water before it enters the manifold jacket, which would
cause the thermostat to stay closed for longer. But, once the water in the
tank is hot, it would work normally.

Can anyone see anything wrong with this? One good thing, is that the over
temperature sensor would warn if the engine gets too hot (because the
thermostat has not opened).

GBM

"Rich Hampel" wrote in message
...
Better to simply 'tap into' the exhaust header outlet hose and 'branch'
into the hot water heater then back to the injection nozzle.

The circuit is a direct connect between the block and the exhaust
manifold on the Q series Yanmars ... so this may be difficult to do as
you propose. Besides, the water will be much hotter coming off the
exhaust manifold.


Rich,
The "exhaust header outlet hose" comes off the thermostat housing. The
housing mixes hot water from the manifold with cold water and then sends it
to the exhaust injection nozzle. So this water is not hot - it has already
been mixed with cold water.

In order to 'tap' into the HOT water exiting the mainifold, I would need to
have a tee that fits between the manifold and the thermostat housing. This
would have to be a custom made part either machined or cast. This location
would provide the most heat.

Actually, on the 2QM15, the circuit is not direct connected between the
block and the manifold - there is a hose that connects from the cylinder
head water outlet to the manifold. It is this hose that I was thinking of
tapping into.

GBM

You are right as I was thinking of the 2QM20 (or 3QM30) ... which is
arranged the way that I stated but has the Tstat in a separate housing
that fits into the top of the fresh water tank on the heat exchanger..


In article , GBM
wrote:

"Rich Hampel" wrote in message
...
Better to simply 'tap into' the exhaust header outlet hose and 'branch'
into the hot water heater then back to the injection nozzle.

The circuit is a direct connect between the block and the exhaust
manifold on the Q series Yanmars ... so this may be difficult to do as
you propose. Besides, the water will be much hotter coming off the
exhaust manifold.


Rich,
The "exhaust header outlet hose" comes off the thermostat housing. The
housing mixes hot water from the manifold with cold water and then sends it
to the exhaust injection nozzle. So this water is not hot - it has already
been mixed with cold water.

In order to 'tap' into the HOT water exiting the mainifold, I would need to
have a tee that fits between the manifold and the thermostat housing. This
would have to be a custom made part either machined or cast. This location
would provide the most heat.

Actually, on the 2QM15, the circuit is not direct connected between the
block and the manifold - there is a hose that connects from the cylinder
head water outlet to the manifold. It is this hose that I was thinking of
tapping into.

GBM

"Rich Hampel" wrote in message
...
You are right as I was thinking of the 2QM20 (or 3QM30) ... which is
arranged the way that I stated but has the Tstat in a separate housing
that fits into the top of the fresh water tank on the heat exchanger..


Rich - What do you think about the fact that the water leaving the heads
would be cooled (In the water heater) before it returns to the manifold. It
would soon get hot again, but the manifold would be slightly cooler than the
block.

And, the thermostat would not open right away (Until water heater is hot),
so engine would presumably run hotter for a while.

GBM

The water temperature will soon reach a steady state once the heater
temperature 'equilibrates'. Typically such a heater will come up to
temp quite fast. My 7 gallon heater will heat to 'hot' water from the
engine loop in about 10-15 minutes. Was the same with an Atomic 4 as
it is with my 3QM30. Actually the cooler the water in the manifold is
actualy better ... less carbonate (salting) deposition.... and heat
transfer is regulated by the 'log mean temperature difference' - the
cooler the inlet water the better the overal heat transfer.

In article , GBM
wrote:

"Rich Hampel" wrote in message
...
You are right as I was thinking of the 2QM20 (or 3QM30) ... which is
arranged the way that I stated but has the Tstat in a separate housing
that fits into the top of the fresh water tank on the heat exchanger..


Rich - What do you think about the fact that the water leaving the heads
would be cooled (In the water heater) before it returns to the manifold. It
would soon get hot again, but the manifold would be slightly cooler than the
block.

And, the thermostat would not open right away (Until water heater is hot),
so engine would presumably run hotter for a while.

GBM

"Rich Hampel" wrote in message
...
The water temperature will soon reach a steady state once the heater
temperature 'equilibrates'. Typically such a heater will come up to
temp quite fast. My 7 gallon heater will heat to 'hot' water from the
engine loop in about 10-15 minutes. Was the same with an Atomic 4 as
it is with my 3QM30. Actually the cooler the water in the manifold is
actualy better ... less carbonate (salting) deposition.... and heat
transfer is regulated by the 'log mean temperature difference' - the
cooler the inlet water the better the overal heat transfer.


Thanks Rich - I think I will try it - It seems such an easy way to get some
hot water without a closed circuit system. Got to order the heater first!

GBM

GBM wrote:
"Rich Hampel" wrote in message
...

The water temperature will soon reach a steady state once the heater
temperature 'equilibrates'. Typically such a heater will come up to
temp quite fast. My 7 gallon heater will heat to 'hot' water from the
engine loop in about 10-15 minutes. Was the same with an Atomic 4 as
it is with my 3QM30. Actually the cooler the water in the manifold is
actualy better ... less carbonate (salting) deposition.... and heat
transfer is regulated by the 'log mean temperature difference' - the
cooler the inlet water the better the overal heat transfer.



Thanks Rich - I think I will try it - It seems such an easy way to get some
hot water without a closed circuit system. Got to order the heater first!

GBM


I'll be curious about the results. From what I've heard,the raw water
systems don't heat the water enough to really heat up a water tank.

My system has an 11 gallon tank on a 2GM20FC (fresh water). When
running hard, the engine water temp gets up to 170+ and the hot water
tank gets fully heated in under 30 minutes. However, when used for
battery charging, the temp barely gets to 160, and the hot water tank
takes the full hour to heat up, and even then its not as hot as when
running hard.

As near as I can tell, the target for the hot water tank is about 160
degrees. IIRC, the PS test heated to 160, and then measured to
cooldown rate - the goal was to have hot water the morning after a run.

I think the tstat on the Yanmar raw water systems is set at 140, but
I've also heard 125 degrees. I don't know if that implies that the
loop you speak of is reduced to this lower temp. Of course, if all
you did was heat the tank to 120 degrees, that would be a big step up
from cold - it just means that you can't count on much heat left a day
later.

"Jeff" wrote in message

I'll be curious about the results. From what I've heard,the raw water
systems don't heat the water enough to really heat up a water tank.

This is usually true because the raw water has either already been cooled by
mixing in cold water, or because the thermostat setting is at 120F or so.
In our case (Yanmar 2QM15), at least we can get at the hot water exiting the
engine before it is mixed with cold.


As near as I can tell, the target for the hot water tank is about 160
degrees. IIRC, the PS test heated to 160, and then measured to
cooldown rate - the goal was to have hot water the morning after a run.

I am sure that this is about right, but depends on how hot the water needs
to be.

I think the tstat on the Yanmar raw water systems is set at 140, but
I've also heard 125 degrees. I don't know if that implies that the
loop you speak of is reduced to this lower temp.

I don't know what it is set at - It is not easy to measure because the water
exiting the manifold is mixed with cold water in the thermostat housing. In
the set up that I am contemplating, the thermostat will actually be setting
the water exiting the water heater coil at say 120 or 140F. The engine will
therefore run hotter than this, but probably not by much - maybe 5 deg max,
until the water in the tank is hot too.

Of course, if all you did was heat the tank to 120 degrees, that would be
a big step up
from cold - it just means that you can't count on much heat left a day
later.

True - But at least it should cool down slower because it the temperature
diff is less to start with If we get luke warm water that will be better
than ice cold. And when heading out, the water should be hot if we use shore
power at the dock. I have thought about getting a Honda 2Kw generator and
that would help when away from shore power, but I need some other
justification to sell the idea!

GBM