Yanmar Water Heater Connections

[expozen]

I'm working on connecting my Isotemp calorifier/water heater to my Yanmar 2GM20f. It seems pretty straight forward. There's just one thing I'm curious about. I can't find any information about whether the thermostat controls flow to only the engine heat exchanger, or both the heat exchanger and the water heater. I'm guessing that it only controls flow to the heat exchanger, and that the pump always pumps to the water heater? So this would mean that by connecting the water heater to engine, it could take longer to reach operating temp (depending on the temp of the water in the water heater)? And also the engine could have more of a propensity to overheat, because once the water heater has absorbed max heat it will then act as if the engine water heater inlet was connected directly to the outlet, mixing hot water with the water that was just cooled from the heat exchanger?

[a64pilot]

Water always flows through the heater hose, it will not have a tendency to overheat. You can plug the hoses, which replicates what it there with no hoses or take a short hose and conned the two.

This is identical to the heater in an automobile. Just it goes to a water heater instead of an air heater is all.

If I’m plugged into a dock, I try to leave with the heater hot, it’s my belief that with the water in the heater being hot, the engine warms up faster because of course that flow of heat goes both ways.

If the heater is cold, you right it will take longer for the engine to warm up fully, cause it has to heat that water in the tank too.

In a properly operating engine there is a rather large excess cooling capacity, it’s designed that way of course, to overheat you really have to lose quit a bit of capacity, which of course can happen.

[DougR]

A64's answer is correct....the water flows all the time.

That said, it is frequent practice to place a restriction in the outlet fitting of the thermostat housing to the water heater line to lower the amount of flow to the heater. It takes a little longer to heat the water up, but after the water in the tank is hot there will be less hot water returned to the engine, and less chance of overheat if the system is marginal.

DougR