Overheating the engine on a mercruiser ib/ob.

The engine cooling fan comes on when the engine temp. reaches around 180 degrees F , The air con fan comes on with the air con switch.

check thermostat , check water is getting up to the engine waterpump , pos blockage !? does water come out the back ? exhausts and risers do corrode and block the out lets !

180--------have radiator tested soon along with the waterpump

The bike should be running at 180 to 190 degrees. It would be impossible for your bike to be running at 100 degrees. Your body temp is 98.6 degrees. Engines are designed to run at higher temps for better combustion.

WELL SOME OF THE OLDER CAR RUN A LITTLE HOTTER THAN NEWER CARS THE COOLANT FAN WOULD TURN ON AROUND 180 TO 190 DEGREES.THE OLDER CAR I REMEMBER THE OLDSMOBILE AND PONTIAC ENGINE RUN A LITTLE HOTTER BACK WHEN I OWN ONE.

195 degrees is the typical high end on the thermostat (when the thermostat opens), so the temp gauge should read a max of 195 degrees, give or take a few degrees. Some people replace their thermostat with a lower temp one, such as a 180 degree one. Then the gauge will read lower (approx 180 degree max). So the range is typically from cold at start to just under 200 degrees.

Normal operating temperature on the bike should not go over 220 degrees F for very long, even in stop & go traffic. Riding down the highway on a hot day you might be 190 F. At start up there won't be a reading until the sensor gets over the minimum which is probably around 100 degrees. You should be able to see it rise after a minute or so of idling. You should hear your fan come on around 190-200 degrees. Your thermostat probably opens at 180, allowing coolant to flow through the radiator and if that does not cool the bike enough the fan comes on next.

I assume there is no manual control for setting temp. so the thermal sensor or control circuit has failed and it is just staying at its maximum.  You will probably get more help from the manufacturer but their website is somewhat disjointed; looking for contact info for your product ends at one point and then shifts to their scientific product line.
The only general contact info I found is here:
Nor-Lake 
You will in any case need to have the correct model number at hand since the subject line doesn't sound like your freezer. 

Clean the Idle Air Control Valve. It's on the throttle body below the Throttle Position Sensor. Worked for me! Good luck.