Idle water pressure is 1 - 3 psi, Wide open throttle is 12 psi. optimax and other di 2 strokes run very hot at idle. Warning buzzer comes on at about 75 celcius, if you leave your boat on idle for long enough the warning will come on, but open the throttle and it should cool very quickly. Although check this with the smartcraft controls so you dont do any damage. If the tempreature doesnt come down consider the thermostats. I think there are 2, one on each cylinder head cover at the top, they are black with a blue piece of plastic round them and lie at the top of the block on eithier bank of cylinders. Here are the instructions from the workshop manual. Use a pan and a thermometer as a thermostat tester
"1. Inspect thermostat covers and cylinder head covers (thermostat opening) for cracks and
corrosion damage that could cause leakage. Replace parts as necessary.
2. Remove and discard gasket from each thermostat.
3. Wash thermostats with clean water.
4. Using a thermostat tester, similar to the one shown, test each thermostat as follows:
a. Open thermostat valve, then insert a thread between valve and thermostat body. Allow
valve to close against thread.
b. Suspend thermostat (from thread) and thermometer inside tester so that neither
touches the container. Bottom of thermometer must be even with bottom of thermostat
to obtain correct temperature of thermostat opening.
c. Fill thermostat tester with water to cover thermostat.
d. Plug tester into electrical outlet.
e. Observe temperature at which thermostat begins to open. (Thermostat will drop off
thread, that was installed in Step “a”, when it starts to open.) Thermostat must begin
to open when temperature reaches 140°-145° F (60°-63° C).
f. Continue to heat water until thermostat is completely open.
g. Unplug thermostat tester.
h. Replace thermostat, if it fails to open at the specified temperature, or if it does not
NOTE: BE SURE that water in thermostat tester is allowed to cool sufficiently [below 110°F
(43.3° C)] before testing the other thermostat."
If they are ok consider the impeller, and i am asuming that you will have checked the inlets for blockage.
hope this helps