Don W wrote:
Hi Roger,

Roger Long wrote:

The heat exchanger in your set up is the key. Simple raw water
systems like mine run way too cool for best diesel engine operation.


Whether an engine is raw-water cooled or cooled through a heat
exchanger should have nothing to do with the temperature
it operates at.

Somewhere in the system should be a thermostat which prevents
new coolant from being pumped into the engine until the
coolant in the block has come up to the proper temperature.
This will work whether the coolant is an antifreeze mixture
pumped through a heat exchanger, or raw water drawn through a
water intake.

Is your thermostat possibly stuck open, or missing? Or am I
missing something here?


Yes, Yanmar (and other manufacturers) use a much lower temp for raw
water cooled engines. I believe it is to reduce precipitation of
salts. The thermostat and alarm are set to much lower temps - the
alarm is at 145 instead of 185 as on fresh water engines.