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