as this engine is with fresh
water cooling without
heat exchanger, temperature should not go higher than 164 degrees F
thermostat should start opening at 140 degrees
if temperature goes higher than this, the
salt in the seawater will cristalise and eventually block the
cooling system
these engines are built to run for days without stop
a good indication of right engine temp : when it is running for some time, you should not be able to hold your hand on the cylinder, but ou shouldn't really burn yourself either
hope this helps