Which also happens to be the dirty little secret about 4-stroke outboards.
4-stroke motors pump more fuel (past the rings) and moisture into the case
than 2-stroke motors ...and the case oil is required for lubrication. Cars
do this all the time, but they run a hot compared to an outboard and the
moisture and fuel evaporates out (and is burned via the exhaust-gas return
(EGR) valve back to the intake.) In a 4-stroke outboard or other 4-stroke
salt-water cooled motor, you can't allow it to run hot enough to effectively
vaporize the moisture and fuel in the oil else you get salt deposits in the
motor. It's tough to design a good 4-stroke motor that runs well, doesn't
get hot enough to salt out, yet runs as hot as it can otherwise. This is
also why you should use only the best oil in your 4-stroke motor and change
it often. And... it's also why inboard 4-strokes are best off with a
freshwater cooling system and thermostat that lets them run hotter than an
outboard could.

Brian d



"bowgus" wrote in message
oups.com...
If you exceed 150F or so with raw salt water cooling, the cooling water
will dump it's salt (a simple heat the salty water, the heated water
can't hold as much salt, the salt gets dumped), clogging up your
cooling system. And that's as far as I know why these thermostats are
around 140 F ...