You may have to add a couple check valves to the sealed coolant side
depending on the type of pumps. A rubber vaned pump will prvent backflow
when it is not spinning. A regular metal vaned pump such as is used on a
marinized car engine will not. You don't give any specifics but I presume
you also have a way to provide the raw water flow no matter which engine is
running? Normally a pump on the engine also provides the raw water flow to
the heat exchanger. If you are also planning to Y the raw side as well the
same issues about check valves would apply. I have not seen appropriate
check valves for this application but I suspect they are available. They
would need to open with minimal forward pressure so check valves designed
for use in a pressurized water supply may not work. On the other hand the
check valves would not have to provide a perfect seal. The additional
complexity in plumbing may make it not worth while. There is something to
be said for simple.

"franc" wrote in message
...
I want to add another, smaller generator to my boat.
Existing and new sets have indirect water cooling.

I have only one heat exchanger and the expense of
adding another seems a little high.

So I was wondering if anybody tried adding a second
generator to the heat exchanger of another engine,
with two Y connectors at the exchanger?
Engines would have a shared indirect cooling system.
Does this work? Do I need to install one-way valves at
the outlets to the cooler to avoid cooling water to run
through the inactive engine, or is that not an issue?
Cooling capacity should be ok for both engines since the
exchanger was sized for a bigger engine (bigger than my
'big' generator) but I intend to run only one genset at
a time anyway.

Thx, Al