We went through the same thing in hooking up coolant
lines from our Yanmar
. The first thing I did was to call the Yanmar
dealer to find out how much 3/4" hose we could use (how far the water heater could be from the engine). Armed with that info, we ran a new 1.25" hose from the thermostat housing down to a valve and tee (so we could create a restriction sending coolant
to the water heater, with some coolant bypassing the water heater), a tee below the valve for the coolant returning from the water heater) and then a section of 1.25" hose heading back to the engine
. Works fine for us.
All this was necessary because our engine does not have a provision for connecting a water heater... unlike many of the newer engines.