You will hear all kinds of opinions. But when it comes down to it, the benefits of the ‘stat is why they put it in there. Benefits such as better, cleaner running in cold weather or cold water. Do you know that OMC sold that same motor (powerhead) on a cheapy lower unit and strangled down to 5hp to compete with Sears, etc? The resulting 5hp did not have a thermostat—then they sold a thermostat kit as an accessory.
EDIT: One service manual says it should run 1500-3000 RPM on a boat @ 125 degree minimum, and less than 163 degrees.
