Don W wrote in news:Xp_Rf.1452
:

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?



I think what's missing is the directly cooled engine has GOT to bypass
water around the engine/thermostat into the hot exhaust to cool it long
before that thermostat ever opens. This means his hose-to-the-exhaust has
COLD water in it before the thermostat opens to cool the exhaust (and the
hot water tank). The amount of water through a thermostat that had bypass
water flowing around it would be miniscule. Outboard motors are like this,
somewhat. The exhaust hardly gets warm, certainly never warm enough to
melt the paint on it....or to heat water in a tank.