OK this is something that seems to be done different ways by different
folks. My water heater plumbing was contributing to my 4-108 over heating.
My plumbing runs from the top of the exaust manifold-water heater-tee at
rear of trany/oil cooler. I put a valve inline and the engine runs cooler
with it closed.
If you go to the yachet broker sites and look at all the endeavour sail
boats you will see engine pics that look like the water heater tees into the
coolant temp sending unit on the head just behind the tank. ether way you go
put a valve inline to give you control.
Good luck. - Allen